000
FXUS63 KILX 031952
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
252 PM CDT FRI JUL 3 2009

.DISCUSSION...
ISSUED 252 PM CDT FRI JUL 3 2009

A QUIET AND SLIGHTLY COOLER THAN NORMAL EARLY SUMMER DAY IS
UNFOLDING ACROSS CENTRAL AND SOUTHEAST ILLINOIS. WHILE IT STARTED
OUT SUNNY...CLOUDS HAVE RETURNED TO THE FORECAST AREA. THE MAJORITY
OF THE FORECAST PERIOD IS EXPECTED TO BE DRY AND SUMMER LIKE.
UNFORTUNATELY...THE BEST PERIOD FOR SIGNIFICANT RAINFALL WILL BE
LATER TONIGHT INTO SATURDAY WITH THE PASSAGE OF A THUNDERSTORM
COMPLEX /MCS/. SO...NOT SURPRISINGLY...THE RAINFALL CHANCES AND
TIMING FOR THE FOURTH OF JULY HOLIDAY ARE THE PRIMARY FORECAST
CONCERN.

12Z MODELS IN REASONABLE AGREEMENT TODAY. HOWEVER...THERE ARE STILL
SOME DIFFERENCES IN THE EXACT PLACEMENT OF THE HEAVY RAINFALL AXIS
WITH THE MCS EXPECTED TO IMPACT THE REGION OVERNIGHT INTO SATURDAY.
THESE DIFFERENCES PERSIST DESPITE A VERY SIMILAR DEPICTION OF WHERE
THE LOW LEVEL BAROCLINIC ZONE AND UPPER FORCING WILL RESIDE DURING
THE PERIOD. IN ANY CASE...EXPECT THE ENTIRE FORECAST AREA TO GET
MEASURABLE RAINFALL...LOCALLY HEAVY.

SHORT TERM...TONIGHT THROUGH MONDAY...

TONIGHT INTO SATURDAY NIGHT...LOW PRESSURE...CURRENTLY DEVELOPING
OVER THE CENTRAL PLAINS...WILL TRACK EAST SOUTHEAST INTO KENTUCKY
AND TENNESSEE BY EARLY SUNDAY. A WARM FRONT CURVES EAST AND
SOUTHEAST FROM THE DEVELOPING LOW. A SOUTHWEST 50 KT LOW LEVEL
JET WILL HELP TRANSPORT COPIOUS AMOUNTS OF MOISTURE INTO THE
DEVELOPING SYSTEM TONIGHT AND DEVELOP A MCS IN THE VICINITY THE
IA/MO BORDER REGION. THIS MCS IS EXPECTED TO CURVE EAST AND
SOUTHEAST ALONG THE WARM FRONT TRACKING ACROSS THE BULK OF THE
FORECAST AREA BY MIDDAY SATURDAY AS THE LOW LEVEL JET VEERS.
ADDITIONAL FORCING FOR THE MCS WILL BE PROVIDED BY THE RIGHT REAR
QUADRANT OF A JET STREAK DIVING SOUTHEAST ACROSS THE GREAT LAKES.
THE RAINFALL MAY BE HEAVY AT TIMES WITH PRECIPITABLE WATER VALUES
ALONG AND AHEAD OF THE SURFACE LOW/MCS TRACK EXPECTED TO BE AROUND
2 INCHES. ONCE THE MCS DEPARTS AROUND MIDDAY...THE POTENTIAL FOR
ADDITIONAL DEVELOPMENT...AS WELL AS HOW WARM TEMPERATURES WILL
GET...WILL BE GOVERNED BY HOW QUICKLY SKIES ARE ABLE TO CLEAR. AT
THIS POINT...FEEL THAT THE BULK OF THE SECONDARY DEVELOPMENT WILL
OCCUR TO THE SOUTH OF THE FORECAST AREA...OR AT LEAST SOUTH OF THE
I-70 CORRIDOR. IN ANY CASE...AM STILL HOPEFUL THAT FIREWORKS WILL
BE ABLE TO GO OFF AS SCHEDULED IN MOST LOCALES AS THE PRECIPITATION
RISK SHIFTS TO OUR SOUTH AND EAST WITH THE SURFACE LOW/FRONT.

SUNDAY AND MONDAY...QUIETER AND SOMEWHAT COOLER WEATHER RETURNS TO
THE REGION AS THE MAIN BAROCLINIC ZONE SETTLES SOUTH OF ILLINOIS AND
HIGH PRESSURE BUILDS INTO THE REGION.

LONG TERM...MONDAY NIGHT THROUGH THURSDAY...MODELS/ENSEMBLES IN
REASONABLE AGREEMENT THROUGH THE EXTENDED RANGE OF THE FORECAST. THE
FLOW ACROSS NORTH AMERICA WILL BE AMPLIFYING AT THE START OF THE
PERIOD WITH A RIDGE WEST/TROF EAST CONFIGURATION. ULTIMATELY...A
BROAD RIDGE WILL BE IN PLACE ACROSS MUCH OF THE LOWER 48 STATES BY
THE END OF THE PERIOD. THIS PROGRESSION WILL RESULT IN NEAR NORMAL
TEMPERATURES ON MONDAY NIGHT/TUESDAY TRENDING MORE HOT/HUMID BY THE
END OF THE WEEK. HAVE MAINTAINED A DRY FORECAST THROUGH THE
PERIOD...WITH NO MAJOR WAVES/SYSTEMS AGREED UPON BY THE MODEL
CONSENSUS.

BAK
&&

.AVIATION...
ISSUED 1250 PM CDT FRI JUL 3 2009

3.5 TO 5K FT CEILINGS WILL OCCUR THIS AFTERNOON ACROSS THE CENTRAL
IL TERMINALS AND SCATTERED OUT LATER TODAY WITH LOSS OF DIURNAL
HEATING EFFECTS. BROKEN CUMULUS CLOUDS FORMED LATE THIS MORNING
FROM TRAPPED MOISTURE AROUND 850 MB LEFT BEHIND FROM 565 DM 500 MB
LOW PRESSURE LIFTING NE INTO THE ST LAWRENCE RIVER VALLEY IN SE
CANADA. CIRRUS CLOUDS ALREADY SPREADING EAST ACROSS CENTRAL IL BY
EARLY AFTERNOON AHEAD OF NEXT STORM SYSTEM IN THE CENTRAL PLAINS
WITH 1011 LOW PRESSURE IN EAST CENTRAL CO AND WARM FRONT LIFTING
NORTHWARD ACROSS KS. A 50+ KT SW LOW LEVEL JET WILL FIRE UP
CONVECTION OVER IOWA DURING THIS EVENING AND SPREAD SE ACROSS
CENTRAL IL OVERNIGHT...REACHING PIA AROUND 07Z/2 AM AND CMI BY
10Z/4 AM. HAVE MVFR CEILINGS. THUNDERSTORMS WITH HEAVY RAINS WILL
LIKELY IMPACT CENTRAL IL AIRPORTS SAT MORNING AND LOWERED VSBYS TO
2 TO 4 MILES WITH CEILINGS OF 1500 TO 2500 FT. THUNDERSTORMS
SHOULD EXIT EAST OF CENTRAL IL BY MIDDAY SAT BUT LINGERING SHOWERS
WITH CEILINGS OF 700 TO 1500 FT POSSIBLE. LIGHT WNW WINDS THIS
AFTERNOON TO BECOME SE 6 TO 8 KTS TONIGHT AND SAT MORNING.

HUETTL
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KILX 031755
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1255 PM CDT FRI JUL 3 2009

.DISCUSSION...
ISSUED 1045 AM CDT FRI JUL 3 2009

UPDATING THE FORECAST FOR MORE CLOUD COVER TODAY ESPECIALLY IN
EASTERN IL WHERE BROKEN CUMULUS CLOUDS QUICKLY DEVELOPED BY LATE
MORNING. OTHERWISE REST OF FORECAST ON TRACK TODAY. WARMER HIGHS
IN THE LOWER 80S WITH LAWRENCEVILLE NEAR 85F. WINDS STAYING LIGHT
AGAIN TODAY WITH NEARBY HIGH PRESSURE.

15Z/10 AM SURFACE MAP SHOWS WEAK 1019 MB HIGH PRESSURE OVER IL/MO.
1011 MB LOW PRESSURE WAS OVER EAST CENTRAL CO WITH A FRONTAL
BOUNDARY OVER SW KS AND NE OK. SHOWERS AND THUNDERSTORMS AHEAD OF
THIS FRONT NEAR THE KS/MO BORDER INTO SW IA. ALOFT A 565 DM 500 MB
LOW WAS ALONG THE SE QUEBEC/ONTARIO PROVINCE LINE WITH 593 DM 500
MB HIGH OVER TX.

MODELS DRIFT WEAK HIGH PRESSURE EAST OF IL TONIGHT WHILE FRONTAL
BOUNDARY LIFTS INTO NORTHERN MO AND SW IL. PARTLY TO MOSTLY CLOUDY
SKIES TO PREVAIL THIS AFTERNOON WITH SHOWERS AND THUNDERSTORMS
DEVELOPING OVERNIGHT. HIGHS IN THE LOWER 80S WITH LAWRENCEVILLE NEAR
85F.

HUETTL

&&

.AVIATION...
ISSUED 1250 PM CDT FRI JUL 3 2009

3.5 TO 5K FT CEILINGS WILL OCCUR THIS AFTEROON ACROSS THE CENTRAL
IL TERMINALS AND SCATTERED OUT LATER TODAY WITH LOSS OF DIRUNAL
HEATING EFFECTS. BROKEN CUMULUS CLOUDS FORMED LATE THIS MORNING
FROM TRAPPED MOISTURE AROUND 850 MB LEFT BEHIND FROM 565 DM 500 MB
LOW PRESSURE LIFTING NE INTO THE ST LAWRENCE RIVER VALLEY IN SE
CANADA. CIRRUS CLOUDS ALREADY SPREADING EAST ACROSS CENTRAL IL BY
EARLY AFTERNOON AHEAD OF NEXT STORM SYSTEM IN THE CENTRAL PLAINS
WITH 1011 LOW PRESSURE IN EAST CENTRAL CO AND WARM FRONT LIFTING
NORTHWARD ACROSS KS. A 50+ KT SW LOW LEVEL JET WILL FIRE UP
CONVECTION OVER IOWA DURING THIS EVENING AND SPREAD SE ACROSS
CENTRAL IL OVERNIGHT...REACHING PIA AROUND 07Z/2 AM AND CMI BY
10Z/4 AM. HAVE MVFR CEILINGS. THUNDERSTORMS WITH HEAVY RAINS WILL
LIKELY IMPACT CENTRAL IL AIRPORTS SAT MORNING AND LOWERED VSBYS TO
2 TO 4 MILES WITH CEILINGS OF 1500 TO 2500 FT. THUNDERSTORMS
SHOULD EXIT EAST OF CENTRAL IL BY MIDDAY SAT BUT LINGERING SHOWERS
WITH CEILINGS OF 700 TO 1500 FT POSSIBLE. LIGHT WNW WINDS THIS
AFTERNOON TO BECOME SE 6 TO 8 KTS TONIGHT AND SAT MORNING.

HUETTL

&&

.PREV DISCUSSION...
ISSUED 304 AM CDT FRI JUL 3 2009

EARLY MORNING SFC MAP INDICATED 1011 MB LOW PRESSURE DEVELOPING
OVER SW KANSAS AND A BROAD AREA OF LOW PRESSURE PULLING NORTHEAST
OF THE GRT LAKES...WITH A WEAK HIGH PRESSURE RIDGE NOSING DOWN ACROSS
THE MS VALLEY. ALOFT...NORTHWEST FLOW CONTINUED OVER THE MIDWEST
AND OH VALLEY...BETWEEN A STRONG RIDGE IN THE SW U.S...AND AN UPPER
LOW EAST OF THE GRT LAKES. W/V IMAGERY SHOWED SUBTROPICAL...MONSOON
MOISTURE PLUME RIDING WEST OF THE UPPER RIDGE AXIS AND SPILLING
INTO THE PLAINS. SIGNIFICANT SHORTWAVE ENERGY SWIRLING OVER NRN UTAH
WILL BE KEY TO OUR WEATHER AS IT TOPS THE RIDGE AND INTERACTS WITH
MOISTURE AND BAROCLINIC ZONE TO THE SW. THE MAIN FORECAST
CHALLENGE IS PLACEMENT OF HEAVY RAIN AXIS LATE FRIDAY NIGHT INTO
SATURDAY. 00Z NAM/GFS MODELS HAVE TRENDED SLISHTLY SLOWER...FARTHER
NORTH...AND A BIT STRONGER WITH THIS SYSTEM...OR SIMILAR TO THE
ECMWF DEPICTION FOR THE PAST TWO DAYS.

SHORT TERM...TODAY THROUGH SATURDAY
EXCELLENT WEATHER CONDITIONS TODAY AS SFC RIDGE SHIFTS ACROSS THE
AREA. UPPER HEIGHTS BUILD AND 850 MB TEMPS RISE INTO THE LOWER
TEENS...YIELDING HIGHS IN THE LOWER 80S...AND SOME MID 80S SOUTH
OF I-70. MORE SUN TO BE SEEN THAN THE PAST FEW DAYS...THOUGH
EXPECT SOME CU DEVELOPMENT GIVEN LINGERING MOISTURE AT H850.
MID/HIGH CLOUDS WILL BE ON THE INCREASE BY LATE AFTERNOON AND
EVENING AHEAD OF DEVELOPING SYSTEM TO THE WEST.

MODERATE TO LOCALLY HEAVY RAINS POSSIBLE LATE TONIGHT AND
SATURDAY MORNING. SFC LOW TO TRACK ESE ALONG BAROCLINIC ZONE WITH
LARGE SCALE LIFT NORTH OF THIS BOUNDARY. DEEP MOISTURE FEED BY 50
KT 850 MB JET DIRECTED INTO THIS BOUNDARY BRINGING HIGH THETA-E
AIR AIMED AT THE WRN CWA BY 12Z SAT. ALSO UPPER DIVERGENCE
BULLSEYE OVER CENTRAL/NRN IL NEAR RR QUAD OF 100 KT UPPER JET
DIVING ACROSS THE GRT LAKES. 00Z MODELS HAVE TRENDED FARTHER NORTH
WITH PLACEMENT OF 850 MB FRONT AND ASSOCIATED HEAVY RAIN AXIS...WITH
NAM NOW FARTHEST NORTH FOCUSING HEAVY RAINS ACROSS NRN CWA...ALSO
IN LINE WITH NEWLY ARRIVED ECMWF. WITH PROGGED AMOUNT OF FORCING
FROM 06Z- 18Z SAT...AND PW/S RISING UP NEAR 2 INCHES...EXPECT A
WIDE SWATH OF 1-2 INCH RAINS NORTH OF I-72 BY EARLY SATURDAY
AFTERNOON WITH LOCALLY HIGHER AMOUNTS DUE TO POSSIBLE TRAINING
CONVECTION. 3 HR FFG VALUES IN EXCESS OF 2 INCHES...SO DO NOT
ANTICIPATE FLOODING ISSUES. SVR POTENTIAL FOR EARLY SATURDAY
MORNING LOOKS LOW DUE TO LACK OF INSTABILITY /MUCAPES BELOW 200
J/KG/ AND SATURATED PROFILES...BUT WITH ROBUST WIND SHEAR SOME
SMALL HAIL IS POSSIBLE MAINLY ON THE SRN FRINGE OF THE COMPLEX IN
MORE ORGANIZED UPDRAFTS. EVOLUTION OF CONVECTIVE SYSTEM WILL BE
KEY TO ANY AFTERNOON RE-DEVELOPMENT SOUTH OF I-72. INSTABILITY
INCREASES ABOVE 1000 J/KG AND BOTH LOW LEVEL AND DEEP LAYER SHEAR
WOULD BE SUFFICIENT FOR SOME STRONG TO SEVERE STORMS AHEAD OF SFC
LOW TRACKING NEAR KSTL BY 00Z...HOWEVER OUTFLOW FROM EARLIER MCS
MAY PUSH THE EFFECTIVE SFC BOUNDARY SOUTH OF THE CWA. SPC HAS
AREAS SOUTH OF A JACKSONVILLE TO CHARLESTON LINE IN DAY 2 SLGT
RISK. GIVEN THE SLOWING TREND OF THIS SYSTEM...HAVE LINGERED LOW
CHC POPS SOUTH OF I-70 FOR SATURDAY NIGHT.

LONG TERM...SUNDAY THROUGH THURSDAY
SFC LOW AND FRONT PRESS SE THROUGH THE OH VALLEY EARLY SUNDAY AS
HIGH PRESSURE BUILDS EAST FROM THE PLAINS. WITH NORTHWEST FLOW
ALOFT...AND N/NE SFC FLOW...TEMPS SHOULD BE NEAR TO SLIGHTLY BELOW
NORMAL THROUGH MONDAY. UPPER RIDGE BUILDS NE TOWARDS THE LOWER LAKES BY
MID-WEEK AND WITH HEIGHTS RISING AND WINDS VEERING AROUND TO THE
SOUTH...MORE HEAT AND HUMIDITY SHOULD BUILD INTO THE MIDWEST.
ATMOSPHERE LOOKS TO BE CAPPED WITH RING OF FIRE PATTERN SETTING UP
WELL NORTH...SO HOT/HUMID BUT DRY CONDITIONS LOOK LIKELY INTO THE
END OF THE WEEK.

25


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 031752
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1252 PM CDT FRI JUL 3 2009

.DISCUSSION...
1250 PM CDT

ANTICIPATE LITTLE CHANGE TO GOING SET OF FORECAST ELEMENTS THROUGH
THE WEEKEND.

MAY TIGHTEN UP POP GRADIENT ACROSS THE FORECAST AREA OVERNIGHT
AND SATURDAY MORNING AS ISENTROPICS...OMEGA...DIVERGENCE AND QPF
FIELDS ALL INDICATE AXIS TO RUN FROM EAST CENTRAL AND SOUTHEAST IA
SOUTHEASTWARD ACROSS CENTRAL IL TO THE MID OH VALLEY FROM LATE
TONIGHT THROUGH SATURDAY. THIS KEEPS SOUTHWEST AND FAR SOUTHERN
PORTION OF THE LOCAL FORECAST AREA IN AREA LIKELY TO RECEIVE RAIN
WHILE FAR NORTH CENTRAL AND NORTHEAST IL MAY SEE LITTLE IN ANY.

OTHER MINOR CHANGE MAY BE TO SLICE A DEGREE OR TWO OFF OF SATURDAY
HIGHS DUE TO LINGERING CLOUDS THOUGH IF ANY BREAKS DEVELOP LATER
IN THE DAY /SUNSET NOT TIL AROUND 830 PM CDT/ TEMPERATURES WILL
RESPOND.

TRS

&&

.AVIATION...
642 AM CDT

1200 UTC TAFS...MAIN AVIATION FORECAST CONCERNS ARE WIND
DIRECTIONS TODAY...AND INCREASING CHANCES OF RAIN TONIGHT.

MAIN FEATURE OF INTEREST THIS MORNING IS A WEAK SFC TROUGH ACROSS
SOUTHEAST WISCONSIN WHICH MARKS A SUBTLE WIND SHIFT FROM THE WEST
TO THE NORTHWEST. THIS TROUGH SHOULD WORK ITS WAY INTO NORTHEAST
ILLINOIS OVER NEXT FEW HOURS. WINDS WELL BEHIND THIS SFC TROUGH
ARE SHIFTING NORTHEAST ACROSS EAST CENTRAL WISCONSIN AND WOULD
EXPECT ORD/MDW/GYY WILL DEVELOP A NORTH NORTHEAST COMPONENT EARLY
TO MID AFTERNOON...AND EVENTUALLY EAST DUE TO FAVORABLE LAKE
BREEZE SETUP WITH WEAK GRADIENT PERSISTING INTO THE AFTERNOON.

VFR STRATOCU DECK WHICH HAS RESIDED ACROSS NORTHERN ILLINOIS FOR MOST
OF THE NIGHT...SHOULD BEGIN TO ERODE THIS MORNING AS AN UPPER
LEVEL SHORT WAVE ACROSS FAR NORTHWEST ILLINOIS DIVES SOUTHEAST
THROUGH UPPER RIDGE. HAVE KEPT A SCT040 MENTION THROUGH THE DAY
WITH EXPECTATION THAT DIURNAL CU SHOULD FORM RATHER QUICKLY THIS
MORNING. OTHERWISE JUST EXPECTING INCREASING HIGH CLOUDINESS
TODAY.

FOR TONIGHT...EASTERLY WINDS WITH THE LAKE BREEZE WILL EVENTUALLY
BECOME MODIFIED TO THE SOUTHEAST BY THE SYNOPTIC GRADIENT AND
REMAIN LIGHT THROUGH THE NIGHT. BIGGER CONCERN TONIGHT WILL BE
POTENTIAL FOR WET RUNWAYS WITH INCREASING RAIN CHANCES. AN UPPER
LEVEL SHORT WAVE TROUGH ACROSS THE CENTRAL PLAINS WILL SHIFT INTO
THE AREA TONIGHT AND WILL BE ACCOMPANIED BY A STRONG LOW LEVEL
JET. AS MENTIONED IN PREVIOUS DISCUSSION...BETTER ISENTROPIC
UPGLIDE SHOULD BE FOCUSED SOUTH OF THE TERMINALS...BUT WITH THE
CENTRAL PLAINS TROUGH MOVING THROUGH THE AREA TONIGHT DID GO AHEAD
AND INCLUDE PREVAILING SHOWER MENTION FROM LATE TONIGHT INTO
SATURDAY MORNING...IN THE 09Z-14Z TIME FRAME EXCEPT A LITTLE
EARLIER AT RFD. RAIN MENTION MAY NEED TO BE EXTENDED LATER IN THE
DAY TOMORROW AS SYSTEM WILL BE SLOW TO PULL OUT. WHILE CANNOT
DISCOUNT POSSIBILITY OF SOME EMBEDDED THUNDER...HAVE CONTINUED TO
OMIT FROM FORECAST AT THIS DISTANCE DUE TO MARGINAL INSTABILITY
AND MORE IMPRESSIVE LOW LEVEL JET FORCING REMAINING TO THE SOUTH OF
THE TERMINALS.

MARSILI

&&

.MARINE...
305 AM CDT

A WEAK SFC TROUGH WILL CONTINUE SOUTHWARD ACROSS SOUTHERN LAKE
MICHIGAN THIS MORNING. WINDS AT THE SOUTHERN BUOY EVEN REPORTING
SOUTHWEST DIRECTIONS IN ADVANCE OF THIS FRONT AS OF 08Z. WINDS
WILL VEER AROUND TO THE NORTHWEST THIS MORNING WITH FRONTAL
PASSAGE...AND THEN LIKELY FAVOR LIGHT NORTHEAST THIS AFTERNOON.
GRADIENT SHOULD BE WEAK ENOUGH TO SUPPORT LAKE BREEZE DEVELOPMENT
THIS AFTERNOON. WHILE WINDS WILL BE RELATIVELY WEAK OVER THE LAKE
TODAY AND TONIGHT...DIRECTIONS BECOME SOMEWHAT TRICKY INTO TONIGHT
DUE TO THE INFLUENCE OF A COUPLE OF DIFFERENT LOW PRESSURE
SYSTEMS. THE STRONGER OF THESE LOW PRESSURE SYSTEMS WILL CONTINUE
TO TAKE SHAPE ACROSS THE CENTRAL PLAINS TONIGHT WHILE A WEAKER LOW
DEVELOPS ACROSS SOUTHERN ONTARIO. AS A RESULT DIRECTIONS SHOULD
BEGIN TO FAVOR MORE OF A SOUTHERLY DIRECTION LATE TONIGHT INTO
SATURDAY. A WEAK SFC TROUGH IS EXPECTED TO TAKE WINDS BACK AROUND
TO THE WEST SATURDAY NIGHT INTO SUNDAY. SPEEDS BEHIND THIS TROUGH
SUNDAY INTO MONDAY SHOULD REMAIN AT OR BELOW 10 KNOTS AND DIMINISH
DURING THE DAY MONDAY AS ANOTHER SFC HIGH BUILDS INTO THE REGION.

MARSILI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KLOT 031738
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1238 PM CDT FRI JUL 3 2009

.DISCUSSION...
400 AM CDT

FORECAST ATTENTION IS ON PRECIP CHANCES/TIMING/TRENDS FOR FIRST HALF
OF HOLIDAY WEEKEND.

IN THE NEAR TERM...UPPER TROUGH WHICH HAS PLAGUED THE EASTERN HALF
OF NORTH AMERICA OVER THE PAST SEVERAL DAYS WILL CONTINUE TO WEAKEN
AND DRIFT EAST TODAY. MODEST HEIGHT RISES IN THE WAKE OF DEPARTING
SYSTEM WILL ALLOW WEAK SURFACE HIGH PRESSURE TO MOVE ACROSS THE
AREA...THOUGH COMBINATION OF LINGERING WEAK CYCLONIC FLOW AND MID
LEVEL SHORT WAVE CROSSING THE AREA THIS MORNING HELPING TO MAINTAIN
SOME CLOUDINESS IN THE FORM OF STRATOCU. WOULD EXPECT HOLES TO
DEVELOP OR INCREASE IN SIZE DURING THE MORNING HOURS AS MINOR
AMPLITUDE SHORT WAVE MOVES AWAY TO THE EAST AND HEIGHT
RISES/SUBSIDENCE DEVELOP...THOUGH WILL LIKELY SEE AN INCREASE IN
HIGH CLOUDS FROM THE WEST THIS AFTERNOON AS A MORE VIGOROUS SHORT
WAVE OVER CENTRAL ROCKIES MOVES INTO THE PLAINS WITH ITS
ASSOCIATED CONVECTION. DESPITE SOME CLOUDINESS...MODERATION OF
TEMPS IN LOW/MID LEVELS CONTINUES WITH DEPARTURE OF EASTERN
TROUGH...WITH LOW LEVEL MODEL THERMAL PROGS SUPPORTING TEMPS IN
AROUND/LOW 80S WITH WARMEST READINGS EXPECTED ACROSS WESTERN CWA
AND COOLER NEAR LAKE MICHIGAN WITH LAKE BREEZE IN WEAK PRESSURE
GRADIENT ASSOCIATED WITH SFC HIGH.

AFOREMENTIONED SHORT WAVE PROPAGATING ACROSS PLAINS WILL APPROACH
THE FORECAST AREA OVERNIGHT TONIGHT. SOUTHERLY RETURN FLOW TO
DEVELOP ACROSS THE SOUTHERN/CENTRAL PLAINS IN RESPONSE...AS SFC LOW
PRESSURE DEVELOPS OVER KANSAS. WRF/GFS SIMILAR IN DEVELOPING 40-50
KT 850 HPA JET INTO ELEVATED BAROCLINIC ZONE FROM SOUTHERN
IA/NORTHERN MO INTO CENTRAL IL THROUGH 12Z SATURDAY. COMBINATION OF
STRONG LOW LEVEL JET AND RESULTING MOISTURE CONVERGENCE/THETA-E
ADVECTION EXPECTED TO RESULT IN THUNDERSTORM/MCS DEVELOPMENT TO MOVE
INTO CENTRAL IL BY EARLY SATURDAY MORNING...AND LIGHTER SHOWERS
FARTHER NORTH ASSOCIATED WITH MID LEVEL WAVE. GREATEST THREAT SHOULD
BE AFTER MIDNIGHT...PERHAPS CLOSER TO SUNRISE...SO MAJORITY OF
EVENING HOLIDAY FESTIVALS SHOULD REMAIN DRY. WRF/GFS PWATS INCREASE
TO 1.8 TO 2.0 INCHES INTO CENTRAL IL BY 12Z SATURDAY...SUGGESTING
POTENTIAL FOR SOME LOCALLY HEAVY RAINFALL PERHAPS JUST SOUTH OF CWA.
MODELS ARE A BIT DIFFERENT ON AXIS OF HEAVIEST QPF...THOUGH BASED ON
MOIST CONVERGENCE AROUND 850 HPA WOULD SUPPORT THE IA/MO BORDER AREA
INTO CENTRAL IL FOR GREATEST THREAT. BASED ON THIS HAVE RAISED POPS
ACROSS THE AREA...WITH CATEGORICAL POPS LATE TONIGHT/SATURDAY
MORNING ACROSS FAR SOUTH COUNTIES OF CWA. FARTHER NORTH...FORECAST
SOUNDINGS SUGGEST LAPSE RATES NOT VERY IMPRESSIVE WITH PERHAPS 200
J/KG OF SHALLOW ELEVATED CAPE AND HAVE KEPT THUNDER MENTION TO
ISOLATED.

SHORT WAVE DAMPENS INTO CONFLUENT MID LEVEL FLOW EARLY SATURDAY...
WEAKENING AND BECOMING ELONGATED AS IT SHEARS OUT IN A WEST/EAST
ORIENTATION OVER CENTRAL IL/IN DURING THE DAY. THIS MAINTAINS AN
AREA OF WEAKER MOIST CONVERGENCE/FRONTOGENETIC FORCING ACROSS
SOUTHERN PORTIONS OF THE CWA DURING THE DAY SATURDAY...WHICH
GRADUALLY WEAKENS THROUGH THE AFTERNOON. UNFORTUNATELY...THIS WOULD
SUGGEST THREAT OF AT LEAST SOME INTERMITTENT SHOWERS ESPECIALLY
SOUTHERN COUNTIES. AGAIN...LAPSE RATES APPEAR PRETTY WEAK AND SHOULD
NOT SUPPORT WIDESPREAD THUNDER BEYOND BETTER LOW LEVEL JET/MOIST
CONVERGENCE PERIOD DURING THE MORNING HOURS. EXPECT MOST PARTS OF
THE CWA TO BE DRY BY EVENING AS SYSTEM CONTINUES TO TRACK SLOWLY OFF
TO THE SOUTHEAST AND AWAY FROM THE AREA AND HIGH PRESSURE BUILDS IN
BEHIND IT. GIVEN DEGREE OF EXPECTED CLOUD COVER AND PRECIP
ESPECIALLY SOUTH HAVE LOWERED TEMPS FOR SATURDAY.

SURFACE HIGH MOVES ACROSS IA ON SUNDAY...WITH SFC RIDGING EXTENDING
EAST INTO FORECAST AREA. GUIDANCE DOES INDICATE ANOTHER SHORT WAVE
DROPPING SOUTHEAST ACROSS THE GREAT LAKES REGION LATE IN THE DAY
WITH A WEAK SURFACE TROUGH DROPPING ACROSS WI. GFS IS ODD SOLUTION
OUT IN BRINGING THIS INTO NORTHERN IL BY 00Z MON...WHILE OTHER
GUIDANCE IS SLOWER AND KEEPS FRONT NORTH OF AREA THROUGH SUNDAY
NIGHT. HAVE FOLLOWED THIS SLOWER APPROACH WHICH KEEPS LOW/SLGT
CHANCE POPS NORTH OF THE IL/WI BORDER AND THE FORECAST DRY FOR THE
END OF THE HOLIDAY WEEKEND. WARMER CONDITIONS EXPECTED AS WELL AS
LOW LEVEL THERMAL PROGS AND MORE SUNSHINE SUPPORT TEMPS BACK NEAR
NORMAL INTO THE LOWER 80S.

NO SIGNIFICANT CHANGES TO DAYS 4-7 AT THIS TIME.

RATZER

&&

.AVIATION...

1800 UTC TAFS...LAKE BREEZE ALREADY IN MOTION AND NEARING MDW
ALREADY SHUD SOON TO BE AT ORD. TEMP DIFFERENTIAL BTWN LAND AND
WATER NOT THAT GREAT AND HOLDING BACK ON CONTINUATION OF BREEZE INTO
DPA. CYCLONIC FLOW INDUCING CU FIELD AROUND 5K. THIS FIELD APPEARS TO
BE THINNING OUT AT RFD ON BACKSIDE OF AN UPPER WAVE. THIS THINNING
MOVING SE WITH THIS WAVE TOWARD OTHER TERMINALS. WILL THUS TAKE CU
SCT EARLY AFTN THEN ADVECT AC AND MORE SC INTO NRN IL THIS EVENING
AHEAD OF A MORE PROMINENT SHORT WAVE FROM THE PLAINS. THIS WAVE
CROSSING THE MS RVR VLY BY MORNING WITH PCPN BEGINNING AT
TERMINALS AROUND THAT TIME. VARIABLE WINDS IN VERY LIGHT PRESSURE
GRADIENT OVERNIGHT WILL LIKELY PICK UP FROM THE SOUTH WITH ONSET
OF PCPN. EVEN WITH LOW LVL JET FEEDING INTO THIS SYSTEM...MAIN SFC
LOW WILL MOVE TO THE EAST ACROSS NRN MO AND CNTL ILLINOIS SATURDAY
WITH MORE SIGNIFICANT CAPES TO THE SOUTH OF THE TERMINALS. SO AM
LEAVING PCPN AS SHOWERS WITH NO MENTION OF TSTMS FOR TERMINALS.
SHOULD BE A LONG PERIOD OF ON AND OFF SHOWERS FROM MORNING INTO
THE EVENING...SATURATING LOWER LAYERS ENUF TO INDUCE MVFR CIGS BY
MID TO LATE AFTN. AS INVERTED TROF MOVES INTO CENTRAL IL
SATURDAY...THE SOUTH WINDS BACK MORE TO THE EAST OFF THE LAKE.

RLB

&&

.MARINE...
1238 PM CDT

WEAK RIDGING BUILDING OVER THE LAKES TODAY WILL KEEP WINDS LIGHT
NORTH TO ALMOST VARIABLE THE REST OF TODAY AND TONIGHT. WINDS
BECOME SOUTHERLY EARLY SATURDAY AS A LOW PRESSURE SYSTEM BUILDS
ACROSS THE PLAINS AND INTO THE MS VLY. THE TIGHTER PRESSURE
GRADIENT FORCES WILL ACTUALLY REMAIN SOUTH OF LK MICHIGAN SATURDAY
THUS KEEPING WIND SPEEDS UNDER 15 KTS AT THE LAKE. THIS SYSTEM
CONTINUES EAST ALONG THE OHIO VLY SAT NIGHT AND SUNDAY...VEERING
WINDS TO THE NW AGAIN OVER LK MICHIGAN. HIGH PRESSURE ATTEMPTS TO
BUILD IN OVER THE LAKES LATE SUNDAY BUT IS INTERRUPTED BY A
SECONDARY WAVE SWINGING AROUND AN ANCHORED UPPER VORTEX IN THE ST
LAWRENCE RIVER VALLEY. WINDS TEMPORARILY BACK TO THE SW AGAIN
SUNDAY NIGHT BEFORE THIS SECONDARY TROF DROPS DOWN THE LAKE. AFTER
THAT...WINDS THEN VEER TO THE NW AGAIN FOR MONDAY AS RATHER
STRONG RIDGING BUILDS OVER THE LAKES REGION.

RLB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KILX 031545
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1045 AM CDT FRI JUL 3 2009

.DISCUSSION...
ISSUED 1045 AM CDT FRI JUL 3 2009

UPDATING THE FORECAST FOR MORE CLOUD COVER TODAY ESPECIALLY IN
EASTERN IL WHERE BROKEN CUMULUS CLOUDS QUICKLY DEVELOPED BY LATE
MORNING. OTHERWISE REST OF FORECAST ON TRACK TODAY. WARMER HIGHS
IN THE LOWER 80S WITH LAWRENCEVILLE NEAR 85F. WINDS STAYING LIGHT
AGAIN TODAY WITH NEARBY HIGH PRESSURE.

15Z/10 AM SURFACE MAP SHOWS WEAK 1019 MB HIGH PRESSURE OVER IL/MO.
1011 MB LOW PRESSURE WAS OVER EAST CENTRAL CO WITH A FRONTAL
BOUNDARY OVER SW KS AND NE OK. SHOWERS AND THUNDERSTORMS AHEAD OF
THIS FRONT NEAR THE KS/MO BORDER INTO SW IA. ALOFT A 565 DM 500 MB
LOW WAS ALONG THE SE QUEBEC/ONTARIO PROVINCE LINE WITH 593 DM 500
MB HIGH OVER TX.

MODELS DRIFT WEAK HIGH PRESSURE EAST OF IL TONIGHT WHILE FRONTAL
BOUNDARY LIFTS INTO NORTHERN MO AND SW IL. PARTLY TO MOSTLY CLOUDY
SKIES TO PREVAIL THIS AFTERNOON WITH SHOWERS AND THUNDERSTORMS
DEVELOPING OVERNIGHT. HIGHS IN THE LOWER 80S WITH LAWRENCEVILLE NEAR
85F.


HUETTL

&&

.AVIATION...
ISSUED 615 AM CDT FRI JUL 3 2009

VFR CONDITIONS ARE EXPECTED THRU THE PERIOD. A FEW LOCATIONS
SEEING SOME PATCHY GROUND FOG THIS MRNG...BUT BELIEVE THAT SHOULD
DISSIPATE/BURN OFF BY 14Z SO WL LIMIT ITS MENTION IN THE TAFS FOR
THIS FCST CYCLE. WEAK HIGH PRESSURE WILL DRIFT ACRS THE MIDWEST
TODAY BRINGING LIGHT WINDS AND A BIT MORE SUNSHINE THAN THE PAST
FEW DAYS. FORECAST SOUNDINGS STILL SHOWING SOME LINGERING MOISTURE
AROUND 850 MB (~5000 FEET) WHICH WILL LEAD TO SOME SCT- BKN CU
LATE THIS MRNG INTO THIS AFTN... ESP IN BMI...DEC AND CMI.
SATELLITE DATA ALREADY INDICATING A BAND OF HI BASED STRATOCU WAS
WORKING ITS WAY SOUTHWARD INTO CNTRL IL.

ATTENTION THEN TURNS TO A FRONTAL SYSTEM THAT WILL BE PUSHING IN
OUR DIRECTION LATER THIS EVENING AND OVERNIGHT. RAIN AND SOME
THUNDERSTORMS ARE EXPECTED ALONG AND NORTH OF THE WARM FRONT LATE
TONIGHT WHICH WILL BE LOCATED OVR N-CNTRL MO EWD TO ARND I-70.
MODELS HAVE TRENDED A BIT SLOWER WITH THIS SYSTEM SO WL BRING RAIN
CHANCES INTO THE WRN TAF SITES AFTR 06Z AND AT OR JUST AFTR 09Z AT
CMI. MAY HAVE TO WATCH FOR MVFR CIGS TO QUICKLY DEVELOP WITH THE
RAIN AREA...ESP ACRS THE WEST TWDS THE END OF THE PERIOD. WL HOLD
OFF MENTIONING AT THIS TIME AS IT APPEARS MOST OF THE LOWER CIGS
WL BE AFTR 12Z SATURDAY.

SMITH

&&

.PREV DISCUSSION...
ISSUED 304 AM CDT FRI JUL 3 2009

EARLY MORNING SFC MAP INDICATED 1011 MB LOW PRESSURE DEVELOPING
OVER SW KANSAS AND A BROAD AREA OF LOW PRESSURE PULLING NORTHEAST
OF THE GRT LAKES...WITH A WEAK HIGH PRESSURE RIDGE NOSING DOWN ACROSS
THE MS VALLEY. ALOFT...NORTHWEST FLOW CONTINUED OVER THE MIDWEST
AND OH VALLEY...BETWEEN A STRONG RIDGE IN THE SW U.S...AND AN UPPER
LOW EAST OF THE GRT LAKES. W/V IMAGERY SHOWED SUBTROPICAL...MONSOON
MOISTURE PLUME RIDING WEST OF THE UPPER RIDGE AXIS AND SPILLING
INTO THE PLAINS. SIGNIFICANT SHORTWAVE ENERGY SWIRLING OVER NRN UTAH
WILL BE KEY TO OUR WEATHER AS IT TOPS THE RIDGE AND INTERACTS WITH
MOISTURE AND BAROCLINIC ZONE TO THE SW. THE MAIN FORECAST
CHALLENGE IS PLACEMENT OF HEAVY RAIN AXIS LATE FRIDAY NIGHT INTO
SATURDAY. 00Z NAM/GFS MODELS HAVE TRENDED SLISHTLY SLOWER...FARTHER
NORTH...AND A BIT STRONGER WITH THIS SYSTEM...OR SIMILAR TO THE
ECMWF DEPICTION FOR THE PAST TWO DAYS.

SHORT TERM...TODAY THROUGH SATURDAY
EXCELLENT WEATHER CONDITIONS TODAY AS SFC RIDGE SHIFTS ACROSS THE
AREA. UPPER HEIGHTS BUILD AND 850 MB TEMPS RISE INTO THE LOWER
TEENS...YIELDING HIGHS IN THE LOWER 80S...AND SOME MID 80S SOUTH
OF I-70. MORE SUN TO BE SEEN THAN THE PAST FEW DAYS...THOUGH
EXPECT SOME CU DEVELOPMENT GIVEN LINGERING MOISTURE AT H850.
MID/HIGH CLOUDS WILL BE ON THE INCREASE BY LATE AFTERNOON AND
EVENING AHEAD OF DEVELOPING SYSTEM TO THE WEST.

MODERATE TO LOCALLY HEAVY RAINS POSSIBLE LATE TONIGHT AND
SATURDAY MORNING. SFC LOW TO TRACK ESE ALONG BAROCLINIC ZONE WITH
LARGE SCALE LIFT NORTH OF THIS BOUNDARY. DEEP MOISTURE FEED BY 50
KT 850 MB JET DIRECTED INTO THIS BOUNDARY BRINGING HIGH THETA-E
AIR AIMED AT THE WRN CWA BY 12Z SAT. ALSO UPPER DIVERGENCE
BULLSEYE OVER CENTRAL/NRN IL NEAR RR QUAD OF 100 KT UPPER JET
DIVING ACROSS THE GRT LAKES. 00Z MODELS HAVE TRENDED FARTHER NORTH
WITH PLACEMENT OF 850 MB FRONT AND ASSOCIATED HEAVY RAIN AXIS...WITH
NAM NOW FARTHEST NORTH FOCUSING HEAVY RAINS ACROSS NRN CWA...ALSO
IN LINE WITH NEWLY ARRIVED ECMWF. WITH PROGGED AMOUNT OF FORCING
FROM 06Z- 18Z SAT...AND PW/S RISING UP NEAR 2 INCHES...EXPECT A
WIDE SWATH OF 1-2 INCH RAINS NORTH OF I-72 BY EARLY SATURDAY
AFTERNOON WITH LOCALLY HIGHER AMOUNTS DUE TO POSSIBLE TRAINING
CONVECTION. 3 HR FFG VALUES IN EXCESS OF 2 INCHES...SO DO NOT
ANTICIPATE FLOODING ISSUES. SVR POTENTIAL FOR EARLY SATURDAY
MORNING LOOKS LOW DUE TO LACK OF INSTABILITY /MUCAPES BELOW 200
J/KG/ AND SATURATED PROFILES...BUT WITH ROBUST WIND SHEAR SOME
SMALL HAIL IS POSSIBLE MAINLY ON THE SRN FRINGE OF THE COMPLEX IN
MORE ORGANIZED UPDRAFTS. EVOLUTION OF CONVECTIVE SYSTEM WILL BE
KEY TO ANY AFTERNOON RE-DEVELOPMENT SOUTH OF I-72. INSTABILITY
INCREASES ABOVE 1000 J/KG AND BOTH LOW LEVEL AND DEEP LAYER SHEAR
WOULD BE SUFFICIENT FOR SOME STRONG TO SEVERE STORMS AHEAD OF SFC
LOW TRACKING NEAR KSTL BY 00Z...HOWEVER OUTFLOW FROM EARLIER MCS
MAY PUSH THE EFFECTIVE SFC BOUNDARY SOUTH OF THE CWA. SPC HAS
AREAS SOUTH OF A JACKSONVILLE TO CHARLESTON LINE IN DAY 2 SLGT
RISK. GIVEN THE SLOWING TREND OF THIS SYSTEM...HAVE LINGERED LOW
CHC POPS SOUTH OF I-70 FOR SATURDAY NIGHT.

LONG TERM...SUNDAY THROUGH THURSDAY
SFC LOW AND FRONT PRESS SE THROUGH THE OH VALLEY EARLY SUNDAY AS
HIGH PRESSURE BUILDS EAST FROM THE PLAINS. WITH NORTHWEST FLOW
ALOFT...AND N/NE SFC FLOW...TEMPS SHOULD BE NEAR TO SLIGHTLY BELOW
NORMAL THROUGH MONDAY. UPPER RIDGE BUILDS NE TOWARDS THE LOWER LAKES BY
MID-WEEK AND WITH HEIGHTS RISING AND WINDS VEERING AROUND TO THE
SOUTH...MORE HEAT AND HUMIDITY SHOULD BUILD INTO THE MIDWEST.
ATMOSPHERE LOOKS TO BE CAPPED WITH RING OF FIRE PATTERN SETTING UP
WELL NORTH...SO HOT/HUMID BUT DRY CONDITIONS LOOK LIKELY INTO THE
END OF THE WEEK.

25

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 031144
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
644 AM CDT FRI JUL 3 2009

.DISCUSSION...
400 AM CDT

FORECAST ATTENTION IS ON PRECIP CHANCES/TIMING/TRENDS FOR FIRST HALF
OF HOLIDAY WEEKEND.

IN THE NEAR TERM...UPPER TROUGH WHICH HAS PLAGUED THE EASTERN HALF
OF NORTH AMERICA OVER THE PAST SEVERAL DAYS WILL CONTINUE TO WEAKEN
AND DRIFT EAST TODAY. MODEST HEIGHT RISES IN THE WAKE OF DEPARTING
SYSTEM WILL ALLOW WEAK SURFACE HIGH PRESSURE TO MOVE ACROSS THE
AREA...THOUGH COMBINATION OF LINGERING WEAK CYCLONIC FLOW AND MID
LEVEL SHORT WAVE CROSSING THE AREA THIS MORNING HELPING TO MAINTAIN
SOME CLOUDINESS IN THE FORM OF STRATOCU. WOULD EXPECT HOLES TO
DEVELOP OR INCREASE IN SIZE DURING THE MORNING HOURS AS MINOR
AMPLITUDE SHORT WAVE MOVES AWAY TO THE EAST AND HEIGHT
RISES/SUBSIDENCE DEVELOP...THOUGH WILL LIKELY SEE AN INCREASE IN
HIGH CLOUDS FROM THE WEST THIS AFTERNOON AS A MORE VIGOROUS SHORT
WAVE OVER CENTRAL ROCKIES MOVES INTO THE PLAINS WITH ITS
ASSOCIATED CONVECTION. DESPITE SOME CLOUDINESS...MODERATION OF
TEMPS IN LOW/MID LEVELS CONTINUES WITH DEPARTURE OF EASTERN
TROUGH...WITH LOW LEVEL MODEL THERMAL PROGS SUPPORTING TEMPS IN
AROUND/LOW 80S WITH WARMEST READINGS EXPECTED ACROSS WESTERN CWA
AND COOLER NEAR LAKE MICHIGAN WITH LAKE BREEZE IN WEAK PRESSURE
GRADIENT ASSOCIATED WITH SFC HIGH.

AFOREMENTIONED SHORT WAVE PROPAGATING ACROSS PLAINS WILL APPROACH
THE FORECAST AREA OVERNIGHT TONIGHT. SOUTHERLY RETURN FLOW TO
DEVELOP ACROSS THE SOUTHERN/CENTRAL PLAINS IN RESPONSE...AS SFC LOW
PRESSURE DEVELOPS OVER KANSAS. WRF/GFS SIMILAR IN DEVELOPING 40-50
KT 850 HPA JET INTO ELEVATED BAROCLINIC ZONE FROM SOUTHERN
IA/NORTHERN MO INTO CENTRAL IL THROUGH 12Z SATURDAY. COMBINATION OF
STRONG LOW LEVEL JET AND RESULTING MOISTURE CONVERGENCE/THETA-E
ADVECTION EXPECTED TO RESULT IN THUNDERSTORM/MCS DEVELOPMENT TO MOVE
INTO CENTRAL IL BY EARLY SATURDAY MORNING...AND LIGHTER SHOWERS
FARTHER NORTH ASSOCIATED WITH MID LEVEL WAVE. GREATEST THREAT SHOULD
BE AFTER MIDNIGHT...PERHAPS CLOSER TO SUNRISE...SO MAJORITY OF
EVENING HOLIDAY FESTIVALS SHOULD REMAIN DRY. WRF/GFS PWATS INCREASE
TO 1.8 TO 2.0 INCHES INTO CENTRAL IL BY 12Z SATURDAY...SUGGESTING
POTENTIAL FOR SOME LOCALLY HEAVY RAINFALL PERHAPS JUST SOUTH OF CWA.
MODELS ARE A BIT DIFFERENT ON AXIS OF HEAVIEST QPF...THOUGH BASED ON
MOIST CONVERGENCE AROUND 850 HPA WOULD SUPPORT THE IA/MO BORDER AREA
INTO CENTRAL IL FOR GREATEST THREAT. BASED ON THIS HAVE RAISED POPS
ACROSS THE AREA...WITH CATEGORICAL POPS LATE TONIGHT/SATURDAY
MORNING ACROSS FAR SOUTH COUNTIES OF CWA. FARTHER NORTH...FORECAST
SOUNDINGS SUGGEST LAPSE RATES NOT VERY IMPRESSIVE WITH PERHAPS 200
J/KG OF SHALLOW ELEVATED CAPE AND HAVE KEPT THUNDER MENTION TO
ISOLATED.

SHORT WAVE DAMPENS INTO CONFLUENT MID LEVEL FLOW EARLY SATURDAY...
WEAKENING AND BECOMING ELONGATED AS IT SHEARS OUT IN A WEST/EAST
ORIENTATION OVER CENTRAL IL/IN DURING THE DAY. THIS MAINTAINS AN
AREA OF WEAKER MOIST CONVERGENCE/FRONTOGENETIC FORCING ACROSS
SOUTHERN PORTIONS OF THE CWA DURING THE DAY SATURDAY...WHICH
GRADUALLY WEAKENS THROUGH THE AFTERNOON. UNFORTUNATELY...THIS WOULD
SUGGEST THREAT OF AT LEAST SOME INTERMITTENT SHOWERS ESPECIALLY
SOUTHERN COUNTIES. AGAIN...LAPSE RATES APPEAR PRETTY WEAK AND SHOULD
NOT SUPPORT WIDESPREAD THUNDER BEYOND BETTER LOW LEVEL JET/MOIST
CONVERGENCE PERIOD DURING THE MORNING HOURS. EXPECT MOST PARTS OF
THE CWA TO BE DRY BY EVENING AS SYSTEM CONTINUES TO TRACK SLOWLY OFF
TO THE SOUTHEAST AND AWAY FROM THE AREA AND HIGH PRESSURE BUILDS IN
BEHIND IT. GIVEN DEGREE OF EXPECTED CLOUD COVER AND PRECIP
ESPECIALLY SOUTH HAVE LOWERED TEMPS FOR SATURDAY.

SURFACE HIGH MOVES ACROSS IA ON SUNDAY...WITH SFC RIDGING EXTENDING
EAST INTO FORECAST AREA. GUIDANCE DOES INDICATE ANOTHER SHORT WAVE
DROPPING SOUTHEAST ACROSS THE GREAT LAKES REGION LATE IN THE DAY
WITH A WEAK SURFACE TROUGH DROPPING ACROSS WI. GFS IS ODD SOLUTION
OUT IN BRINGING THIS INTO NORTHERN IL BY 00Z MON...WHILE OTHER
GUIDANCE IS SLOWER AND KEEPS FRONT NORTH OF AREA THROUGH SUNDAY
NIGHT. HAVE FOLLOWED THIS SLOWER APPROACH WHICH KEEPS LOW/SLGT
CHANCE POPS NORTH OF THE IL/WI BORDER AND THE FORECAST DRY FOR THE
END OF THE HOLIDAY WEEKEND. WARMER CONDITIONS EXPECTED AS WELL AS
LOW LEVEL THERMAL PROGS AND MORE SUNSHINE SUPPORT TEMPS BACK NEAR
NORMAL INTO THE LOWER 80S.

NO SIGNIFICANT CHANGES TO DAYS 4-7 AT THIS TIME.

RATZER

&&

.AVIATION...
642 AM CDT

1200 UTC TAFS...MAIN AVIATION FORECAST CONCERNS ARE WIND
DIRECTIONS TODAY...AND INCREASING CHANCES OF RAIN TONIGHT.

MAIN FEATURE OF INTEREST THIS MORNING IS A WEAK SFC TROUGH ACROSS
SOUTHEAST WISCONSIN WHICH MARKS A SUBTLE WIND SHIFT FROM THE WEST
TO THE NORTHWEST. THIS TROUGH SHOULD WORK ITS WAY INTO NORTHEAST
ILLINOIS OVER NEXT FEW HOURS. WINDS WELL BEHIND THIS SFC TROUGH
ARE SHIFTING NORTHEAST ACROSS EAST CENTRAL WISCONSIN AND WOULD
EXPECT ORD/MDW/GYY WILL DEVELOP A NORTH NORTHEAST COMPONENT EARLY
TO MID AFTERNOON...AND EVENTUALLY EAST DUE TO FAVORABLE LAKE
BREEZE SETUP WITH WEAK GRADIENT PERSISTING INTO THE AFTERNOON.

VFR STRATOCU DECK WHICH HAS RESIDED ACROSS NORTHERN ILLINOIS FOR MOST
OF THE NIGHT...SHOULD BEGIN TO ERODE THIS MORNING AS AN UPPER
LEVEL SHORT WAVE ACROSS FAR NORTHWEST ILLINOIS DIVES SOUTHEAST
THROUGH UPPER RIDGE. HAVE KEPT A SCT040 MENTION THROUGH THE DAY
WITH EXPECTATION THAT DIURNAL CU SHOULD FORM RATHER QUICKLY THIS
MORNING. OTHERWISE JUST EXPECTING INCREASING HIGH CLOUDINESS
TODAY.

FOR TONIGHT...EASTERLY WINDS WITH THE LAKE BREEZE WILL EVENTUALLY
BECOME MODIFIED TO THE SOUTHEAST BY THE SYNOPTIC GRADIENT AND
REMAIN LIGHT THROUGH THE NIGHT. BIGGER CONCERN TONIGHT WILL BE
POTENTIAL FOR WET RUNWAYS WITH INCREASING RAIN CHANCES. AN UPPER
LEVEL SHORT WAVE TROUGH ACROSS THE CENTRAL PLAINS WILL SHIFT INTO
THE AREA TONIGHT AND WILL BE ACCOMPANIED BY A STRONG LOW LEVEL
JET. AS MENTIONED IN PREVIOUS DISCUSSION...BETTER ISENTROPIC
UPGLIDE SHOULD BE FOCUSED SOUTH OF THE TERMINALS...BUT WITH THE
CENTRAL PLAINS TROUGH MOVING THROUGH THE AREA TONIGHT DID GO AHEAD
AND INCLUDE PREVAILING SHOWER MENTION FROM LATE TONIGHT INTO
SATURDAY MORNING...IN THE 09Z-14Z TIME FRAME EXCEPT A LITTLE
EARLIER AT RFD. RAIN MENTION MAY NEED TO BE EXTENDED LATER IN THE
DAY TOMORROW AS SYSTEM WILL BE SLOW TO PULL OUT. WHILE CANNOT
DISCOUNT POSSIBILITY OF SOME EMBEDDED THUNDER...HAVE CONTINUED TO
OMIT FROM FORECAST AT THIS DISTANCE DUE TO MARGINAL INSTABILITY
AND MORE IMPRESSIVE LOW LEVEL JET FORCING REMAINING TO THE SOUTH OF
THE TERMINALS.

MARSILI

&&

.MARINE...
305 AM CDT

A WEAK SFC TROUGH WILL CONTINUE SOUTHWARD ACROSS SOUTHERN LAKE
MICHIGAN THIS MORNING. WINDS AT THE SOUTHERN BUOY EVEN REPORTING
SOUTHWEST DIRECTIONS IN ADVANCE OF THIS FRONT AS OF 08Z. WINDS
WILL VEER AROUND TO THE NORTHWEST THIS MORNING WITH FRONTAL
PASSAGE...AND THEN LIKELY FAVOR LIGHT NORTHEAST THIS AFTERNOON.
GRADIENT SHOULD BE WEAK ENOUGH TO SUPPORT LAKE BREEZE DEVELOPMENT
THIS AFTERNOON. WHILE WINDS WILL BE RELATIVELY WEAK OVER THE LAKE
TODAY AND TONIGHT...DIRECTIONS BECOME SOMEWHAT TRICKY INTO TONIGHT
DUE TO THE INFLUENCE OF A COUPLE OF DIFFERENT LOW PRESSURE
SYSTEMS. THE STRONGER OF THESE LOW PRESSURE SYSTEMS WILL CONTINUE
TO TAKE SHAPE ACROSS THE CENTRAL PLAINS TONIGHT WHILE A WEAKER LOW
DEVELOPS ACROSS SOUTHERN ONTARIO. AS A RESULT DIRECTIONS SHOULD
BEGIN TO FAVOR MORE OF A SOUTHERLY DIRECTION LATE TONIGHT INTO
SATURDAY. A WEAK SFC TROUGH IS EXPECTED TO TAKE WINDS BACK AROUND
TO THE WEST SATURDAY NIGHT INTO SUNDAY. SPEEDS BEHIND THIS TROUGH
SUNDAY INTO MONDAY SHOULD REMAIN AT OR BELOW 10 KNOTS AND DIMINISH
DURING THE DAY MONDAY AS ANOTHER SFC HIGH BUILDS INTO THE REGION.

MARSILI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KILX 031127
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
627 AM CDT FRI JUL 3 2009

.DISCUSSION...
ISSUED 304 AM CDT FRI JUL 3 2009

EARLY MORNING SFC MAP INDICATED 1011 MB LOW PRESSURE DEVELOPING
OVER SW KANSAS AND A BROAD AREA OF LOW PRESSURE PULLING NORTHEAST
OF THE GRT LAKES...WITH A WEAK HIGH PRESSURE RIDGE NOSING DOWN ACROSS
THE MS VALLEY. ALOFT...NORTHWEST FLOW CONTINUED OVER THE MIDWEST
AND OH VALLEY...BETWEEN A STRONG RIDGE IN THE SW U.S...AND AN UPPER
LOW EAST OF THE GRT LAKES. W/V IMAGERY SHOWED SUBTROPICAL...MONSOON
MOISTURE PLUME RIDING WEST OF THE UPPER RIDGE AXIS AND SPILLING
INTO THE PLAINS. SIGNIFICANT SHORTWAVE ENERGY SWIRLING OVER NRN UTAH
WILL BE KEY TO OUR WEATHER AS IT TOPS THE RIDGE AND INTERACTS WITH
MOISTURE AND BAROCLINIC ZONE TO THE SW. THE MAIN FORECAST
CHALLENGE IS PLACEMENT OF HEAVY RAIN AXIS LATE FRIDAY NIGHT INTO
SATURDAY. 00Z NAM/GFS MODELS HAVE TRENDED SLISHTLY SLOWER...FARTHER
NORTH...AND A BIT STRONGER WITH THIS SYSTEM...OR SIMILAR TO THE
ECMWF DEPICTION FOR THE PAST TWO DAYS.

SHORT TERM...TODAY THROUGH SATURDAY
EXCELLENT WEATHER CONDITIONS TODAY AS SFC RIDGE SHIFTS ACROSS THE
AREA. UPPER HEIGHTS BUILD AND 850 MB TEMPS RISE INTO THE LOWER
TEENS...YIELDING HIGHS IN THE LOWER 80S...AND SOME MID 80S SOUTH
OF I-70. MORE SUN TO BE SEEN THAN THE PAST FEW DAYS...THOUGH
EXPECT SOME CU DEVELOPMENT GIVEN LINGERING MOISTURE AT H850.
MID/HIGH CLOUDS WILL BE ON THE INCREASE BY LATE AFTERNOON AND
EVENING AHEAD OF DEVELOPING SYSTEM TO THE WEST.

MODERATE TO LOCALLY HEAVY RAINS POSSIBLE LATE TONIGHT AND
SATURDAY MORNING. SFC LOW TO TRACK ESE ALONG BAROCLINIC ZONE WITH
LARGE SCALE LIFT NORTH OF THIS BOUNDARY. DEEP MOISTURE FEED BY 50
KT 850 MB JET DIRECTED INTO THIS BOUNDARY BRINGING HIGH THETA-E
AIR AIMED AT THE WRN CWA BY 12Z SAT. ALSO UPPER DIVERGENCE
BULLSEYE OVER CENTRAL/NRN IL NEAR RR QUAD OF 100 KT UPPER JET
DIVING ACROSS THE GRT LAKES. 00Z MODELS HAVE TRENDED FARTHER NORTH
WITH PLACEMENT OF 850 MB FRONT AND ASSOCIATED HEAVY RAIN AXIS...WITH
NAM NOW FARTHEST NORTH FOCUSING HEAVY RAINS ACROSS NRN CWA...ALSO
IN LINE WITH NEWLY ARRIVED ECMWF. WITH PROGGED AMOUNT OF FORCING
FROM 06Z- 18Z SAT...AND PW/S RISING UP NEAR 2 INCHES...EXPECT A
WIDE SWATH OF 1-2 INCH RAINS NORTH OF I-72 BY EARLY SATURDAY
AFTERNOON WITH LOCALLY HIGHER AMOUNTS DUE TO POSSIBLE TRAINING
CONVECTION. 3 HR FFG VALUES IN EXCESS OF 2 INCHES...SO DO NOT
ANTICIPATE FLOODING ISSUES. SVR POTENTIAL FOR EARLY SATURDAY
MORNING LOOKS LOW DUE TO LACK OF INSTABILITY /MUCAPES BELOW 200
J/KG/ AND SATURATED PROFILES...BUT WITH ROBUST WIND SHEAR SOME
SMALL HAIL IS POSSIBLE MAINLY ON THE SRN FRINGE OF THE COMPLEX IN
MORE ORGANIZED UPDRAFTS. EVOLUTION OF CONVECTIVE SYSTEM WILL BE
KEY TO ANY AFTERNOON RE-DEVELOPMENT SOUTH OF I-72. INSTABILITY
INCREASES ABOVE 1000 J/KG AND BOTH LOW LEVEL AND DEEP LAYER SHEAR
WOULD BE SUFFICIENT FOR SOME STRONG TO SEVERE STORMS AHEAD OF SFC
LOW TRACKING NEAR KSTL BY 00Z...HOWEVER OUTFLOW FROM EARLIER MCS
MAY PUSH THE EFFECTIVE SFC BOUNDARY SOUTH OF THE CWA. SPC HAS
AREAS SOUTH OF A JACKSONVILLE TO CHARLESTON LINE IN DAY 2 SLGT
RISK. GIVEN THE SLOWING TREND OF THIS SYSTEM...HAVE LINGERED LOW
CHC POPS SOUTH OF I-70 FOR SATURDAY NIGHT.

LONG TERM...SUNDAY THROUGH THURSDAY
SFC LOW AND FRONT PRESS SE THROUGH THE OH VALLEY EARLY SUNDAY AS
HIGH PRESSURE BUILDS EAST FROM THE PLAINS. WITH NORTHWEST FLOW
ALOFT...AND N/NE SFC FLOW...TEMPS SHOULD BE NEAR TO SLIGHTLY BELOW
NORMAL THROUGH MONDAY. UPPER RIDGE BUILDS NE TOWARDS THE LOWER LAKES BY
MID-WEEK AND WITH HEIGHTS RISING AND WINDS VEERING AROUND TO THE
SOUTH...MORE HEAT AND HUMIDITY SHOULD BUILD INTO THE MIDWEST.
ATMOSPHERE LOOKS TO BE CAPPED WITH RING OF FIRE PATTERN SETTING UP
WELL NORTH...SO HOT/HUMID BUT DRY CONDITIONS LOOK LIKELY INTO THE
END OF THE WEEK.

25


&&

.AVIATION...
ISSUED 615 AM CDT FRI JUL 3 2009

VFR CONDITIONS ARE EXPECTED THRU THE PERIOD. A FEW LOCATIONS
SEEING SOME PATCHY GROUND FOG THIS MRNG...BUT BELIEVE THAT SHOULD
DISSIPATE/BURN OFF BY 14Z SO WL LIMIT ITS MENTION IN THE TAFS FOR
THIS FCST CYCLE. WEAK HIGH PRESSURE WILL DRIFT ACRS THE MIDWEST
TODAY BRINGING LIGHT WINDS AND A BIT MORE SUNSHINE THAN THE PAST
FEW DAYS. FORECAST SOUNDINGS STILL SHOWING SOME LINGERING MOISTURE
AROUND 850 MB (~5000 FEET) WHICH WILL LEAD TO SOME SCT- BKN CU
LATE THIS MRNG INTO THIS AFTN... ESP IN BMI...DEC AND CMI.
SATELLITE DATA ALREADY INDICATING A BAND OF HI BASED STRATOCU WAS
WORKING ITS WAY SOUTHWARD INTO CNTRL IL.

ATTENTION THEN TURNS TO A FRONTAL SYSTEM THAT WILL BE PUSHING IN
OUR DIRECTION LATER THIS EVENING AND OVERNIGHT. RAIN AND SOME
THUNDERSTORMS ARE EXPECTED ALONG AND NORTH OF THE WARM FRONT LATE
TONIGHT WHICH WILL BE LOCATED OVR N-CNTRL MO EWD TO ARND I-70.
MODELS HAVE TRENDED A BIT SLOWER WITH THIS SYSTEM SO WL BRING RAIN
CHANCES INTO THE WRN TAF SITES AFTR 06Z AND AT OR JUST AFTR 09Z AT
CMI. MAY HAVE TO WATCH FOR MVFR CIGS TO QUICKLY DEVELOP WITH THE
RAIN AREA...ESP ACRS THE WEST TWDS THE END OF THE PERIOD. WL HOLD
OFF MENTIONING AT THIS TIME AS IT APPEARS MOST OF THE LOWER CIGS
WL BE AFTR 12Z SATURDAY.

SMITH
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 030902
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
402 AM CDT FRI JUL 3 2009

.DISCUSSION...
400 AM CDT

FORECAST ATTENTION IS ON PRECIP CHANCES/TIMING/TRENDS FOR FIRST HALF
OF HOLIDAY WEEKEND.

IN THE NEAR TERM...UPPER TROUGH WHICH HAS PLAGUED THE EASTERN HALF
OF NORTH AMERICA OVER THE PAST SEVERAL DAYS WILL CONTINUE TO WEAKEN
AND DRIFT EAST TODAY. MODEST HEIGHT RISES IN THE WAKE OF DEPARTING
SYSTEM WILL ALLOW WEAK SURFACE HIGH PRESSURE TO MOVE ACROSS THE
AREA...THOUGH COMBINATION OF LINGERING WEAK CYCLONIC FLOW AND MID
LEVEL SHORT WAVE CROSSING THE AREA THIS MORNING HELPING TO MAINTAIN
SOME CLOUDINESS IN THE FORM OF STRATOCU. WOULD EXPECT HOLES TO
DEVELOP OR INCREASE IN SIZE DURING THE MORNING HOURS AS MINOR
AMPLITUDE SHORT WAVE MOVES AWAY TO THE EAST AND HEIGHT
RISES/SUBSIDENCE DEVELOP...THOUGH WILL LIKELY SEE AN INCREASE IN
HIGH CLOUDS FROM THE WEST THIS AFTERNOON AS A MORE VIGOROUS SHORT
WAVE OVER CENTRAL ROCKIES MOVES INTO THE PLAINS WITH ITS
ASSOCIATED CONVECTION. DESPITE SOME CLOUDINESS...MODERATION OF
TEMPS IN LOW/MID LEVELS CONTINUES WITH DEPARTURE OF EASTERN
TROUGH...WITH LOW LEVEL MODEL THERMAL PROGS SUPPORTING TEMPS IN
AROUND/LOW 80S WITH WARMEST READINGS EXPECTED ACROSS WESTERN CWA
AND COOLER NEAR LAKE MICHIGAN WITH LAKE BREEZE IN WEAK PRESSURE
GRADIENT ASSOCIATED WITH SFC HIGH.

AFOREMENTIONED SHORT WAVE PROPAGATING ACROSS PLAINS WILL APPROACH
THE FORECAST AREA OVERNIGHT TONIGHT. SOUTHERLY RETURN FLOW TO
DEVELOP ACROSS THE SOUTHERN/CENTRAL PLAINS IN RESPONSE...AS SFC LOW
PRESSURE DEVELOPS OVER KANSAS. WRF/GFS SIMILAR IN DEVELOPING 40-50
KT 850 HPA JET INTO ELEVATED BAROCLINIC ZONE FROM SOUTHERN
IA/NORTHERN MO INTO CENTRAL IL THROUGH 12Z SATURDAY. COMBINATION OF
STRONG LOW LEVEL JET AND RESULTING MOISTURE CONVERGENCE/THETA-E
ADVECTION EXPECTED TO RESULT IN THUNDERSTORM/MCS DEVELOPMENT TO MOVE
INTO CENTRAL IL BY EARLY SATURDAY MORNING...AND LIGHTER SHOWERS
FARTHER NORTH ASSOCIATED WITH MID LEVEL WAVE. GREATEST THREAT SHOULD
BE AFTER MIDNIGHT...PERHAPS CLOSER TO SUNRISE...SO MAJORITY OF
EVENING HOLIDAY FESTIVALS SHOULD REMAIN DRY. WRF/GFS PWATS INCREASE
TO 1.8 TO 2.0 INCHES INTO CENTRAL IL BY 12Z SATURDAY...SUGGESTING
POTENTIAL FOR SOME LOCALLY HEAVY RAINFALL PERHAPS JUST SOUTH OF CWA.
MODELS ARE A BIT DIFFERENT ON AXIS OF HEAVIEST QPF...THOUGH BASED ON
MOIST CONVERGENCE AROUND 850 HPA WOULD SUPPORT THE IA/MO BORDER AREA
INTO CENTRAL IL FOR GREATEST THREAT. BASED ON THIS HAVE RAISED POPS
ACROSS THE AREA...WITH CATEGORICAL POPS LATE TONIGHT/SATURDAY
MORNING ACROSS FAR SOUTH COUNTIES OF CWA. FARTHER NORTH...FORECAST
SOUNDINGS SUGGEST LAPSE RATES NOT VERY IMPRESSIVE WITH PERHAPS 200
J/KG OF SHALLOW ELEVATED CAPE AND HAVE KEPT THUNDER MENTION TO
ISOLATED.

SHORT WAVE DAMPENS INTO CONFLUENT MID LEVEL FLOW EARLY SATURDAY...
WEAKENING AND BECOMING ELONGATED AS IT SHEARS OUT IN A WEST/EAST
ORIENTATION OVER CENTRAL IL/IN DURING THE DAY. THIS MAINTAINS AN
AREA OF WEAKER MOIST CONVERGENCE/FRONTOGENETIC FORCING ACROSS
SOUTHERN PORTIONS OF THE CWA DURING THE DAY SATURDAY...WHICH
GRADUALLY WEAKENS THROUGH THE AFTERNOON. UNFORTUNATELY...THIS WOULD
SUGGEST THREAT OF AT LEAST SOME INTERMITTENT SHOWERS ESPECIALLY
SOUTHERN COUNTIES. AGAIN...LAPSE RATES APPEAR PRETTY WEAK AND SHOULD
NOT SUPPORT WIDESPREAD THUNDER BEYOND BETTER LOW LEVEL JET/MOIST
CONVERGENCE PERIOD DURING THE MORNING HOURS. EXPECT MOST PARTS OF
THE CWA TO BE DRY BY EVENING AS SYSTEM CONTINUES TO TRACK SLOWLY OFF
TO THE SOUTHEAST AND AWAY FROM THE AREA AND HIGH PRESSURE BUILDS IN
BEHIND IT. GIVEN DEGREE OF EXPECTED CLOUD COVER AND PRECIP
ESPECIALLY SOUTH HAVE LOWERED TEMPS FOR SATURDAY.

SURFACE HIGH MOVES ACROSS IA ON SUNDAY...WITH SFC RIDGING EXTENDING
EAST INTO FORECAST AREA. GUIDANCE DOES INDICATE ANOTHER SHORT WAVE
DROPPING SOUTHEAST ACROSS THE GREAT LAKES REGION LATE IN THE DAY
WITH A WEAK SURFACE TROUGH DROPPING ACROSS WI. GFS IS ODD SOLUTION
OUT IN BRINGING THIS INTO NORTHERN IL BY 00Z MON...WHILE OTHER
GUIDANCE IS SLOWER AND KEEPS FRONT NORTH OF AREA THROUGH SUNDAY
NIGHT. HAVE FOLLOWED THIS SLOWER APPROACH WHICH KEEPS LOW/SLGT
CHANCE POPS NORTH OF THE IL/WI BORDER AND THE FORECAST DRY FOR THE
END OF THE HOLIDAY WEEKEND. WARMER CONDITIONS EXPECTED AS WELL AS
LOW LEVEL THERMAL PROGS AND MORE SUNSHINE SUPPORT TEMPS BACK NEAR
NORMAL INTO THE LOWER 80S.

NO SIGNIFICANT CHANGES TO DAYS 4-7 AT THIS TIME.

RATZER

&&

.AVIATION...
1255 AM CDT

0600 UTC TAFS...NO SIGNIFICANT CHANGES FROM PREVIOUS TAFS FOR THE
06Z FORECAST WITH MAIN FORECAST CONCERNS ON WIND TRENDS
TODAY...AND THEN PRECIP CHANCES TONIGHT.

SOME VFR STRATOCU WILL PERSIST ACROSS THE TERMINALS EARLY THIS
MORNING WITH A WEAK GRADIENT IN PLACE AND WEAK LOW LEVEL THETA-E
ADVECTION IN ADVANCE OF A WEAK SHORT WAVE TRACKING OUT OF EASTERN
IOWA. WOULD EXPECT SOME DECREASE IN STRATOCU COVERAGE POSSIBLE
TOWARD MORNING AS THIS SHORT WAVE MOVES OFF TO EAST.
OTHERWISE...QUIET CONDITIONS IN STORE TODAY...WITH MAIN FOCUS ON
WIND DIRECTION TRENDS. A WEAK SURFACE TROUGH CURRENTLY ACROSS EAST
CENTRAL WISCONSIN SHOULD MOVE INTO NORTHEAST ILLINOIS THIS
AFTERNOON AS A STRONGER NORTHERN STREAM SHORT WAVE TRACKS ACROSS
SOUTHERN ONTARIO. CURRENT THINKING IS THAT NORTHWEST WINDS OF 10
KNOTS OR LESS WILL BECOME NORTH NORTHEAST AT ORD/MDW IN THE 19Z-
21Z TIME FRAME AS THIS TROUGH PASSES THROUGH...WITH WINDS LIKELY
REMAINING WEST ACROSS REMAINDER OF TERMINALS. WEAKNESS OF GRADIENT
BEHIND THIS SFC TROUGH SHOULD ALSO SUPPORT A WEAK LAKE BREEZE
DEVELOPING...THAT WOULD LIKELY AFFECT ORD/MDW CLOSER TO 23Z.
FOR SKY COVER...WILL LIKELY HAVE SOME VFR SCT STRATOCU DEVELOP TODAY
WITH STEEP LOW LEVEL LAPSE RATES AND ADEQUATE LOW LEVEL MOISTURE
FOR CU FORMATION...ALONG WITH SOME INCREASING HIGH CLOUDS.

CONCERN TONIGHT WILL SHIFT TO APPROACHING MID/UPPER LEVEL SYSTEM
CURRENTLY ACROSS THE CENTRAL PLAINS. MODELS ARE IN GENERAL AGREEMENT
IN DEVELOPING FAIRLY STRONG LOW LEVEL JET IN ADVANCE OF THIS SHORT
WAVE TONIGHT...WITH BEST LOW LEVEL MOISTURE CONVERGENCE SETTING UP
SOUTH OF THE TERMINALS. 850-500 HPA Q-VEC CONVG ALSO SUPPORTS BEST
FORCING STAYING SOUTH OF TERMINALS...BUT WOULD SUSPECT WITH
STRENGTH ISENTROPIC LIFT AND INCREASING UPPER FORCING WILL HAVE
SOME SHOWERS ACROSS FAR NORTH CENTRAL AND NORTHEAST ILLINOIS. HAVE
TRENDED TAFS TO VCSH MENTION NOW FOR THE END OF THE TAF PERIOD BUT
MAY NEED TO CONSIDER UPGRADING THIS MENTION WITH THE NEXT TAF
ISSUANCE. SOME EMBEDDED THUNDER MAY ALSO BE POSSIBLE...BUT AGAIN A
HIGHER POTENTIAL SOUTH OF THE TERMINALS.

MARSILI

&&

.MARINE...
305 AM CDT

A WEAK SFC TROUGH WILL CONTINUE SOUTHWARD ACROSS SOUTHERN LAKE
MICHIGAN THIS MORNING. WINDS AT THE SOUTHERN BUOY EVEN REPORTING
SOUTHWEST DIRECTIONS IN ADVANCE OF THIS FRONT AS OF 08Z. WINDS
WILL VEER AROUND TO THE NORTHWEST THIS MORNING WITH FRONTAL
PASSAGE...AND THEN LIKELY FAVOR LIGHT NORTHEAST THIS AFTERNOON.
GRADIENT SHOULD BE WEAK ENOUGH TO SUPPORT LAKE BREEZE DEVELOPMENT
THIS AFTERNOON. WHILE WINDS WILL BE RELATIVELY WEAK OVER THE LAKE
TODAY AND TONIGHT...DIRECTIONS BECOME SOMEWHAT TRICKY INTO TONIGHT
DUE TO THE INFLUENCE OF A COUPLE OF DIFFERENT LOW PRESSURE
SYSTEMS. THE STRONGER OF THESE LOW PRESSURE SYSTEMS WILL CONTINUE
TO TAKE SHAPE ACROSS THE CENTRAL PLAINS TONIGHT WHILE A WEAKER LOW
DEVELOPS ACROSS SOUTHERN ONTARIO. AS A RESULT DIRECTIONS SHOULD
BEGIN TO FAVOR MORE OF A SOUTHERLY DIRECTION LATE TONIGHT INTO
SATURDAY. A WEAK SFC TROUGH IS EXPECTED TO TAKE WINDS BACK AROUND
TO THE WEST SATURDAY NIGHT INTO SUNDAY. SPEEDS BEHIND THIS TROUGH
SUNDAY INTO MONDAY SHOULD REMAIN AT OR BELOW 10 KNOTS AND DIMINISH
DURING THE DAY MONDAY AS ANOTHER SFC HIGH BUILDS INTO THE REGION.

MARSILI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KLOT 030813
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
313 AM CDT FRI JUL 3 2009

.DISCUSSION...
247 PM CDT

QUESTION ON THE MIND OF MOST IS WHAT DOES HOLIDAY WEEKEND LOOK.
ONLY A CHANCE OF SHOWERS AND THUNDERSTORMS FROM LATE FRIDAY NIGHT
INTO SATURDAY AND STILL LOOKS THREAT WILL BE MAINLY FROM FAR
SOUTHERN IA AND NORTHERN MO SOUTHEASTWARD ACROSS CENTRAL IL TO
SOUTHERN IN. HAVE SOME SLIGHT CHANCE AND CHANCE POPS EXTENDING INTO
PORTION OF N CENTRAL AND NE IL OVERNIGHT FRI AND FOR SAT
MORNING.

UPPER LOW OVER THE EASTERN GREAT LAKES CONTINUES TO VERY GRADUALLY
SHIFT EASTWARD ALLOWING MID/UPPER RIDGING TO BUILD OVER THE UPPER
MS VALLEY AND SHIFT TRAILING EDGE OF MAIN AREA OF STRATOCU DECK
ALSO EASTWARD...THOUGH EFFECTIVE CLEARING SLOWED BY DIURNAL
DEVELOPMENT ON PERIPHERY. AS SUN LOWERS CLEARING TO JUMP TO THE
EAST AS DIURNAL STRATOCU DISSIPATES.

DE-AMPLIFICATION OF PATTER TO CONTINUE OVERNIGHT THOUGH BROAD
UPPER MEAN TROF TO REMAIN OVER EASTERN CANADA AND NEW ENGLAND FRI
AS STRONG SHORT WAVE CURRENTLY OVER THE MANITOBA-ND BORDER DROPS
SE ACROSS THE N WOODS AND NORTHERN GREAT LAKES TONIGHT THRU SAT.

PUSHING OF LOW POPS A LITTLE FURTHER N ACROSS THE FA FOR LATE FRI
NIGHT AND SAT MORNING IS IN DEFERENCE TO LATEST SREF AND GFS
ENSEMBLE OUTPUTS BRUSHING N CENTRAL AN NE IL WITH LOWER END POPS
AND LIGHT QPFS AS SHORT WAVE TOPS BROAD ROCKIES/HI PLAINS RIDGE
FRI AND THEN DROPS SOUTHEASTWARD ACROSS THE MID MO AND MID MS
VALLEYS DURING FRI NIGHT AND EARLY SAT MORNING...CONTINUING TO THE
LOWER OH VALLEY BY EARLY SAT AFTERNOON. EXPECT AXIS OF QPF TO
EXTEND FROM FAR SOUTHERN IA/NORTHERN MO SE ACROSS W CENTRAL AND SE
IL TO THE LOWER OH RIVER SO CHANCE POPS ACROSS W AND S PORTIONS OF
LOCAL FA DECREASING TO SLIGHT CHANCE FURTHER N AND NE LATE FRI
NIGHT AND SAT MORNING...WITH LINGERING CHANCE POPS ACROSS FAR S
FOR SAT AFTERNOON TIL SHORT WAVE PULLS AWAY.

REST OF WEEKEND DRY WITH NW FLOW PERSISTING. THIS FLOW TO ALSO
KEEPS TEMPS WELL MODERATED WITH READINGS A BIT BELOW NORMS THO
THIS TIME OF YEAR THIS IS STILL COMFORTABLE. SURFACE RIDGE TO MOVE
OVER THE REGION ALLOWING LAKE BREEZE DEVELOPMENT. WITH SOUTHERN
LAKE MI WATER TEMPS NOW INTO THE MID AND UPPER 60S THIS WILL ALLOW
EVEN NEAR-LAKE AREAS TO REACH MID 70S.

NO REAL PROSPECTS FOR SIGNIFICANT THREAT OF RAIN MON THRU THU OF
NEXT WEEK AS COOL DRY NW FLOW PERSISTS.

TRS

&&

.AVIATION...
1255 AM CDT

0600 UTC TAFS...NO SIGNIFICANT CHANGES FROM PREVIOUS TAFS FOR THE
06Z FORECAST WITH MAIN FORECAST CONCERNS ON WIND TRENDS
TODAY...AND THEN PRECIP CHANCES TONIGHT.

SOME VFR STRATOCU WILL PERSIST ACROSS THE TERMINALS EARLY THIS
MORNING WITH A WEAK GRADIENT IN PLACE AND WEAK LOW LEVEL THETA-E
ADVECTION IN ADVANCE OF A WEAK SHORT WAVE TRACKING OUT OF EASTERN
IOWA. WOULD EXPECT SOME DECREASE IN STRATOCU COVERAGE POSSIBLE
TOWARD MORNING AS THIS SHORT WAVE MOVES OFF TO EAST.
OTHERWISE...QUIET CONDITIONS IN STORE TODAY...WITH MAIN FOCUS ON
WIND DIRECTION TRENDS. A WEAK SURFACE TROUGH CURRENTLY ACROSS EAST
CENTRAL WISCONSIN SHOULD MOVE INTO NORTHEAST ILLINOIS THIS
AFTERNOON AS A STRONGER NORTHERN STREAM SHORT WAVE TRACKS ACROSS
SOUTHERN ONTARIO. CURRENT THINKING IS THAT NORTHWEST WINDS OF 10
KNOTS OR LESS WILL BECOME NORTH NORTHEAST AT ORD/MDW IN THE 19Z-
21Z TIME FRAME AS THIS TROUGH PASSES THROUGH...WITH WINDS LIKELY
REMAINING WEST ACROSS REMAINDER OF TERMINALS. WEAKNESS OF GRADIENT
BEHIND THIS SFC TROUGH SHOULD ALSO SUPPORT A WEAK LAKE BREEZE
DEVELOPING...THAT WOULD LIKELY AFFECT ORD/MDW CLOSER TO 23Z.
FOR SKY COVER...WILL LIKELY HAVE SOME VFR SCT STRATOCU DEVELOP TODAY
WITH STEEP LOW LEVEL LAPSE RATES AND ADEQUATE LOW LEVEL MOISTURE
FOR CU FORMATION...ALONG WITH SOME INCREASING HIGH CLOUDS.

CONCERN TONIGHT WILL SHIFT TO APPROACHING MID/UPPER LEVEL SYSTEM
CURRENTLY ACROSS THE CENTRAL PLAINS. MODELS ARE IN GENERAL AGREEMENT
IN DEVELOPING FAIRLY STRONG LOW LEVEL JET IN ADVANCE OF THIS SHORT
WAVE TONIGHT...WITH BEST LOW LEVEL MOISTURE CONVERGENCE SETTING UP
SOUTH OF THE TERMINALS. 850-500 HPA Q-VEC CONVG ALSO SUPPORTS BEST
FORCING STAYING SOUTH OF TERMINALS...BUT WOULD SUSPECT WITH
STRENGTH ISENTROPIC LIFT AND INCREASING UPPER FORCING WILL HAVE
SOME SHOWERS ACROSS FAR NORTH CENTRAL AND NORTHEAST ILLINOIS. HAVE
TRENDED TAFS TO VCSH MENTION NOW FOR THE END OF THE TAF PERIOD BUT
MAY NEED TO CONSIDER UPGRADING THIS MENTION WITH THE NEXT TAF
ISSUANCE. SOME EMBEDDED THUNDER MAY ALSO BE POSSIBLE...BUT AGAIN A
HIGHER POTENTIAL SOUTH OF THE TERMINALS.

MARSILI

&&

.MARINE...
305 AM CDT

A WEAK SFC TROUGH WILL CONTINUE SOUTHWARD ACROSS SOUTHERN LAKE
MICHIGAN THIS MORNING. WINDS AT THE SOUTHERN BUOY EVEN REPORTING
SOUTHWEST DIRECTIONS IN ADVANCE OF THIS FRONT AS OF 08Z. WINDS
WILL VEER AROUND TO THE NORTHWEST THIS MORNING WITH FRONTAL
PASSAGE...AND THEN LIKELY FAVOR LIGHT NORTHEAST THIS AFTERNOON.
GRADIENT SHOULD BE WEAK ENOUGH TO SUPPORT LAKE BREEZE DEVELOPMENT
THIS AFTERNOON. WHILE WINDS WILL BE RELATIVELY WEAK OVER THE LAKE
TODAY AND TONIGHT...DIRECTIONS BECOME SOMEWHAT TRICKY INTO TONIGHT
DUE TO THE INFLUENCE OF A COUPLE OF DIFFERENT LOW PRESSURE
SYSTEMS. THE STRONGER OF THESE LOW PRESSURE SYSTEMS WILL CONTINUE
TO TAKE SHAPE ACROSS THE CENTRAL PLAINS TONIGHT WHILE A WEAKER LOW
DEVELOPS ACROSS SOUTHERN ONTARIO. AS A RESULT DIRECTIONS SHOULD
BEGIN TO FAVOR MORE OF A SOUTHERLY DIRECTION LATE TONIGHT INTO
SATURDAY. A WEAK SFC TROUGH IS EXPECTED TO TAKE WINDS BACK AROUND
TO THE WEST SATURDAY NIGHT INTO SUNDAY. SPEEDS BEHIND THIS TROUGH
SUNDAY INTO MONDAY SHOULD REMAIN AT OR BELOW 10 KNOTS AND DIMINISH
DURING THE DAY MONDAY AS ANOTHER SFC HIGH BUILDS INTO THE REGION.

MARSILI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KILX 030804
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
304 AM CDT FRI JUL 3 2009

.DISCUSSION...
ISSUED 304 AM CDT FRI JUL 3 2009

EARLY MORNING SFC MAP INDICATED 1011 MB LOW PRESSURE DEVELOPING
OVER SW KANSAS AND A BROAD AREA OF LOW PRESSURE PULLING NORTHEAST
OF THE GRT LAKES...WITH A WEAK HIGH PRESSURE RIDGE NOSING DOWN ACROSS
THE MS VALLEY. ALOFT...NORTHWEST FLOW CONTINUED OVER THE MIDWEST
AND OH VALLEY...BETWEEN A STRONG RIDGE IN THE SW U.S...AND AN UPPER
LOW EAST OF THE GRT LAKES. W/V IMAGERY SHOWED SUBTROPICAL...MONSOON
MOISTURE PLUME RIDING WEST OF THE UPPER RIDGE AXIS AND SPILLING
INTO THE PLAINS. SIGNIFICANT SHORTWAVE ENERGY SWIRLING OVER NRN UTAH
WILL BE KEY TO OUR WEATHER AS IT TOPS THE RIDGE AND INTERACTS WITH
MOISTURE AND BAROCLINIC ZONE TO THE SW. THE MAIN FORECAST
CHALLENGE IS PLACEMENT OF HEAVY RAIN AXIS LATE FRIDAY NIGHT INTO
SATURDAY. 00Z NAM/GFS MODELS HAVE TRENDED SLISHTLY SLOWER...FARTHER
NORTH...AND A BIT STRONGER WITH THIS SYSTEM...OR SIMILAR TO THE
ECMWF DEPICTION FOR THE PAST TWO DAYS.

SHORT TERM...TODAY THROUGH SATURDAY
EXCELLENT WEATHER CONDITIONS TODAY AS SFC RIDGE SHIFTS ACROSS THE
AREA. UPPER HEIGHTS BUILD AND 850 MB TEMPS RISE INTO THE LOWER
TEENS...YIELDING HIGHS IN THE LOWER 80S...AND SOME MID 80S SOUTH
OF I-70. MORE SUN TO BE SEEN THAN THE PAST FEW DAYS...THOUGH
EXPECT SOME CU DEVELOPMENT GIVEN LINGERING MOISTURE AT H850.
MID/HIGH CLOUDS WILL BE ON THE INCREASE BY LATE AFTERNOON AND
EVENING AHEAD OF DEVELOPING SYSTEM TO THE WEST.

MODERATE TO LOCALLY HEAVY RAINS POSSIBLE LATE TONIGHT AND
SATURDAY MORNING. SFC LOW TO TRACK ESE ALONG BAROCLINIC ZONE WITH
LARGE SCALE LIFT NORTH OF THIS BOUNDARY. DEEP MOISTURE FEED BY 50
KT 850 MB JET DIRECTED INTO THIS BOUNDARY BRINGING HIGH THETA-E
AIR AIMED AT THE WRN CWA BY 12Z SAT. ALSO UPPER DIVERGENCE
BULLSEYE OVER CENTRAL/NRN IL NEAR RR QUAD OF 100 KT UPPER JET
DIVING ACROSS THE GRT LAKES. 00Z MODELS HAVE TRENDED FARTHER NORTH
WITH PLACEMENT OF 850 MB FRONT AND ASSOCIATED HEAVY RAIN AXIS...WITH
NAM NOW FARTHEST NORTH FOCUSING HEAVY RAINS ACROSS NRN CWA...ALSO
IN LINE WITH NEWLY ARRIVED ECMWF. WITH PROGGED AMOUNT OF FORCING
FROM 06Z- 18Z SAT...AND PW/S RISING UP NEAR 2 INCHES...EXPECT A
WIDE SWATH OF 1-2 INCH RAINS NORTH OF I-72 BY EARLY SATURDAY
AFTERNOON WITH LOCALLY HIGHER AMOUNTS DUE TO POSSIBLE TRAINING
CONVECTION. 3 HR FFG VALUES IN EXCESS OF 2 INCHES...SO DO NOT
ANTICIPATE FLOODING ISSUES. SVR POTENTIAL FOR EARLY SATURDAY
MORNING LOOKS LOW DUE TO LACK OF INSTABILITY /MUCAPES BELOW 200
J/KG/ AND SATURATED PROFILES...BUT WITH ROBUST WIND SHEAR SOME
SMALL HAIL IS POSSIBLE MAINLY ON THE SRN FRINGE OF THE COMPLEX IN
MORE ORGANIZED UPDRAFTS. EVOLUTION OF CONVECTIVE SYSTEM WILL BE
KEY TO ANY AFTERNOON RE-DEVELOPMENT SOUTH OF I-72. INSTABILITY
INCREASES ABOVE 1000 J/KG AND BOTH LOW LEVEL AND DEEP LAYER SHEAR
WOULD BE SUFFICIENT FOR SOME STRONG TO SEVERE STORMS AHEAD OF SFC
LOW TRACKING NEAR KSTL BY 00Z...HOWEVER OUTFLOW FROM EARLIER MCS
MAY PUSH THE EFFECTIVE SFC BOUNDARY SOUTH OF THE CWA. SPC HAS
AREAS SOUTH OF A JACKSONVILLE TO CHARLESTON LINE IN DAY 2 SLGT
RISK. GIVEN THE SLOWING TREND OF THIS SYSTEM...HAVE LINGERED LOW
CHC POPS SOUTH OF I-70 FOR SATURDAY NIGHT.

LONG TERM...SUNDAY THROUGH THURSDAY
SFC LOW AND FRONT PRESS SE THROUGH THE OH VALLEY EARLY SUNDAY AS
HIGH PRESSURE BUILDS EAST FROM THE PLAINS. WITH NORTHWEST FLOW
ALOFT...AND N/NE SFC FLOW...TEMPS SHOULD BE NEAR TO SLIGHTLY BELOW
NORMAL THROUGH MONDAY. UPPER RIDGE BUILDS NE TOWARDS THE LOWER LAKES BY
MID-WEEK AND WITH HEIGHTS RISING AND WINDS VEERING AROUND TO THE
SOUTH...MORE HEAT AND HUMIDITY SHOULD BUILD INTO THE MIDWEST.
ATMOSPHERE LOOKS TO BE CAPPED WITH RING OF FIRE PATTERN SETTING UP
WELL NORTH...SO HOT/HUMID BUT DRY CONDITIONS LOOK LIKELY INTO THE
END OF THE WEEK.

25

&&

.AVIATION...
ISSUED 1150 PM CDT THU JUL 2 2009

CLOUD COVER IS SLOWER DIMINISHING FROM ALL TAF SITES...WITH CMI
AND BMI LIKELY THE LAST ONES TO SEE MOSTLY CLEAR SKIES...SO WILL
KEEP A SHORT TEMPO GROUP OF BKN CIGS FOR THESE TWO SITES EARLY.
SKC FORECAST FOR REMAINDER OF SITES OVERNIGHT. CU RULE STILL HAS
SOME SCT CU DEVELOPING OVER ALL SITES TOMORROW...ALONG WITH A
LITTLE BIT OF CIRRUS. ADDITIONAL MID CLOUDS WILL ADVECT OVER THE
SITES TOMORROW EVENING IN ADVANCE OF THE NEXT EXPECTED WEATHER
MAKER DEVELOPS IN THE PLAINS TOMORROW. LIGHT WINDS WILL BECOME
WESTERLY TOMORROW AS A SFC RIDGE MOVES INTO THE AREA...FOLLOWED BY
LIGHT WINDS DURING THE EVENING HOURS.

AUTEN
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 030555
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1255 AM CDT FRI JUL 3 2009

.DISCUSSION...
247 PM CDT

QUESTION ON THE MIND OF MOST IS WHAT DOES HOLIDAY WEEKEND LOOK.
ONLY A CHANCE OF SHOWERS AND THUNDERSTORMS FROM LATE FRIDAY NIGHT
INTO SATURDAY AND STILL LOOKS THREAT WILL BE MAINLY FROM FAR
SOUTHERN IA AND NORTHERN MO SOUTHEASTWARD ACROSS CENTRAL IL TO
SOUTHERN IN. HAVE SOME SLIGHT CHANCE AND CHANCE POPS EXTENDING INTO
PORTION OF N CENTRAL AND NE IL OVERNIGHT FRI AND FOR SAT
MORNING.

UPPER LOW OVER THE EASTERN GREAT LAKES CONTINUES TO VERY GRADUALLY
SHIFT EASTWARD ALLOWING MID/UPPER RIDGING TO BUILD OVER THE UPPER
MS VALLEY AND SHIFT TRAILING EDGE OF MAIN AREA OF STRATOCU DECK
ALSO EASTWARD...THOUGH EFFECTIVE CLEARING SLOWED BY DIURNAL
DEVELOPMENT ON PERIPHERY. AS SUN LOWERS CLEARING TO JUMP TO THE
EAST AS DIURNAL STRATOCU DISSIPATES.

DE-AMPLIFICATION OF PATTER TO CONTINUE OVERNIGHT THOUGH BROAD
UPPER MEAN TROF TO REMAIN OVER EASTERN CANADA AND NEW ENGLAND FRI
AS STRONG SHORT WAVE CURRENTLY OVER THE MANITOBA-ND BORDER DROPS
SE ACROSS THE N WOODS AND NORTHERN GREAT LAKES TONIGHT THRU SAT.

PUSHING OF LOW POPS A LITTLE FURTHER N ACROSS THE FA FOR LATE FRI
NIGHT AND SAT MORNING IS IN DEFERENCE TO LATEST SREF AND GFS
ENSEMBLE OUTPUTS BRUSHING N CENTRAL AN NE IL WITH LOWER END POPS
AND LIGHT QPFS AS SHORT WAVE TOPS BROAD ROCKIES/HI PLAINS RIDGE
FRI AND THEN DROPS SOUTHEASTWARD ACROSS THE MID MO AND MID MS
VALLEYS DURING FRI NIGHT AND EARLY SAT MORNING...CONTINUING TO THE
LOWER OH VALLEY BY EARLY SAT AFTERNOON. EXPECT AXIS OF QPF TO
EXTEND FROM FAR SOUTHERN IA/NORTHERN MO SE ACROSS W CENTRAL AND SE
IL TO THE LOWER OH RIVER SO CHANCE POPS ACROSS W AND S PORTIONS OF
LOCAL FA DECREASING TO SLIGHT CHANCE FURTHER N AND NE LATE FRI
NIGHT AND SAT MORNING...WITH LINGERING CHANCE POPS ACROSS FAR S
FOR SAT AFTERNOON TIL SHORT WAVE PULLS AWAY.

REST OF WEEKEND DRY WITH NW FLOW PERSISTING. THIS FLOW TO ALSO
KEEPS TEMPS WELL MODERATED WITH READINGS A BIT BELOW NORMS THO
THIS TIME OF YEAR THIS IS STILL COMFORTABLE. SURFACE RIDGE TO MOVE
OVER THE REGION ALLOWING LAKE BREEZE DEVELOPMENT. WITH SOUTHERN
LAKE MI WATER TEMPS NOW INTO THE MID AND UPPER 60S THIS WILL ALLOW
EVEN NEAR-LAKE AREAS TO REACH MID 70S.

NO REAL PROSPECTS FOR SIGNIFICANT THREAT OF RAIN MON THRU THU OF
NEXT WEEK AS COOL DRY NW FLOW PERSISTS.

TRS

&&

.AVIATION...
1255 AM CDT

0600 UTC TAFS...NO SIGNIFICANT CHANGES FROM PREVIOUS TAFS FOR THE
06Z FORECAST WITH MAIN FORECAST CONCERNS ON WIND TRENDS
TODAY...AND THEN PRECIP CHANCES TONIGHT.

SOME VFR STRATOCU WILL PERSIST ACROSS THE TERMINALS EARLY THIS
MORNING WITH A WEAK GRADIENT IN PLACE AND WEAK LOW LEVEL THETA-E
ADVECTION IN ADVANCE OF A WEAK SHORT WAVE TRACKING OUT OF EASTERN
IOWA. WOULD EXPECT SOME DECREASE IN STRATOCU COVERAGE POSSIBLE
TOWARD MORNING AS THIS SHORT WAVE MOVES OFF TO EAST.
OTHERWISE...QUIET CONDITIONS IN STORE TODAY...WITH MAIN FOCUS ON
WIND DIRECTION TRENDS. A WEAK SURFACE TROUGH CURRENTLY ACROSS EAST
CENTRAL WISCONSIN SHOULD MOVE INTO NORTHEAST ILLINOIS THIS
AFTERNOON AS A STRONGER NORTHERN STREAM SHORT WAVE TRACKS ACROSS
SOUTHERN ONTARIO. CURRENT THINKING IS THAT NORTHWEST WINDS OF 10
KNOTS OR LESS WILL BECOME NORTH NORTHEAST AT ORD/MDW IN THE 19Z-
21Z TIME FRAME AS THIS TROUGH PASSES THROUGH...WITH WINDS LIKELY
REMAINING WEST ACROSS REMAINDER OF TERMINALS. WEAKNESS OF GRADIENT
BEHIND THIS SFC TROUGH SHOULD ALSO SUPPORT A WEAK LAKE BREEZE
DEVELOPING...THAT WOULD LIKELY AFFECT ORD/MDW CLOSER TO 23Z.
FOR SKY COVER...WILL LIKELY HAVE SOME VFR SCT STRATOCU DEVELOP TODAY
WITH STEEP LOW LEVEL LAPSE RATES AND ADEQUATE LOW LEVEL MOISTURE
FOR CU FORMATION...ALONG WITH SOME INCREASING HIGH CLOUDS.

CONCERN TONIGHT WILL SHIFT TO APPROACHING MID/UPPER LEVEL SYSTEM
CURRENTLY ACROSS THE CENTRAL PLAINS. MODELS ARE IN GENERAL AGREEMENT
IN DEVELOPING FAIRLY STRONG LOW LEVEL JET IN ADVANCE OF THIS SHORT
WAVE TONIGHT...WITH BEST LOW LEVEL MOISTURE CONVERGENCE SETTING UP
SOUTH OF THE TERMINALS. 850-500 HPA Q-VEC CONVG ALSO SUPPORTS BEST
FORCING STAYING SOUTH OF TERMINALS...BUT WOULD SUSPECT WITH
STRENGTH ISENTROPIC LIFT AND INCREASING UPPER FORCING WILL HAVE
SOME SHOWERS ACROSS FAR NORTH CENTRAL AND NORTHEAST ILLINOIS. HAVE
TRENDED TAFS TO VCSH MENTION NOW FOR THE END OF THE TAF PERIOD BUT
MAY NEED TO CONSIDER UPGRADING THIS MENTION WITH THE NEXT TAF
ISSUANCE. SOME EMBEDDED THUNDER MAY ALSO BE POSSIBLE...BUT AGAIN A
HIGHER POTENTIAL SOUTH OF THE TERMINALS.

MARSILI

&&

.MARINE...
245 AM CDT

LARGE UPPER LOW PRESSURE AROUND GEORGIAN BAY WILL CONTINUE A SLOW
DRIFT EASTWARD TO WESTERN QUEBEC TONIGHT. WEAK HIGH PRESSURE WILL
THEN BUILD ACROSS THE WESTERN GREAT LAKES TONIGHT AND FRIDAY AND
ANCHOR THERE ACROSS THE UPPER GREAT LAKES THROUGH THE UPCOMING
WEEKEND. WEAK RIDGING WILL BRING LIGHT WINDS TO LAKE MICHIGAN
TONIGHT THROUGH THE WEEKEND.

RLB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KILX 030448
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1148 PM CDT THU JUL 2 2009

.DISCUSSION...
ISSUED 900 PM CDT THU JUL 2 2009

CLOUD COVER IS DISSIPATING AS EXPECTED BUT SOME CLOUDS ARE STILL
AROUND...SO PARTLY CLOUDY SKIES FOR NOW LOOKS FINE. TEMPS SHOULD ALSO
FALL AS EXPECTED WITH WINDS BECOMING LIGHT. THEREFORE CURRENT
FORECAST LOOKS FINE AND NOT UPDATE REQUIRED AT THIS TIME.

AUTEN
&&

.AVIATION...
ISSUED 1150 PM CDT THU JUL 2 2009

CLOUD COVER IS SLOWER DIMINISHING FROM ALL TAF SITES...WITH CMI
AND BMI LIKELY THE LAST ONES TO SEE MOSTLY CLEAR SKIES...SO WILL
KEEP A SHORT TEMPO GROUP OF BKN CIGS FOR THESE TWO SITES EARLY.
SKC FORECAST FOR REMAINDER OF SITES OVERNIGHT. CU RULE STILL HAS
SOME SCT CU DEVELOPING OVER ALL SITES TOMORROW...ALONG WITH A
LITTLE BIT OF CIRRUS. ADDITIONAL MID CLOUDS WILL ADVECT OVER THE
SITES TOMORROW EVENING IN ADVANCE OF THE NEXT EXPECTED WEATHER
MAKER DEVELOPS IN THE PLAINS TOMORROW. LIGHT WINDS WILL BECOME
WESTERLY TOMORROW AS A SFC RIDGE MOVES INTO THE AREA...FOLLOWED BY
LIGHT WINDS DURING THE EVENING HOURS.

AUTEN
&&

.PREV DISCUSSION...
ISSUED 259 PM CDT THU JUL 2 2009

PERSISTENT UPPER/SURFACE LOW CONTINUES TO SPIN OVER THE GREAT
LAKES/NORTHERN ONTARIO THIS AFTERNOON. CLOUDS CONTINUE TO SPILL OVER
THE FORECAST AREA IN THE WRAP AROUND MOISTURE ON THE BACK OF THIS
SYSTEM. THE DEPARTURE OF THIS SYSTEM TONIGHT/FRIDAY AND PASSAGE OF
A MCS FRIDAY NIGHT/EARLY SATURDAY ARE THE PRIMARY FORECAST CONCERNS
THIS PACKAGE AS THE REMAINDER OF THE FORECAST PERIOD LOOKS PRETTY
QUIET.

12Z MODELS ARE IN GOOD OVERALL AGREEMENT THROUGH THE PERIOD. THE
BIGGEST DIFFERENCE IN SENSIBLE WEATHER IS IN THE TRACK OF THE
EXPECTED MCS FRIDAY NIGHT/EARLY SATURDAY. THE ECMWF/CANADIAN REMAIN
FURTHER NORTH WITH THE QPF AXIS THAN THE GFS/NAM...DESPITE THE FACT
THAT THEY LARGELY AGREE ON THE LOW LEVEL THERMAL GRADIENT AND UPPER
DYNAMICS. GOING FORECAST AND CONCEPTUAL MODELS FAVOR THE GFS/NAM
SOLUTION AND WILL CONTINUE TO FAVOR THIS TRACK. GUIDANCE
TEMPERATURES GENERALLY CLOSE/REASONABLE. HOWEVER...TEMPERATURES
TONIGHT WILL BE LARGELY IMPACTED BY HOW QUICKLY SKIES CLEAR...WITH
TEMPERATURES FRIDAY NIGHT/SATURDAY BEING MODULATED BY THE EXPECTED
MCS.

SHORT TERM...TONIGHT THROUGH SUNDAY...

TONIGHT AND FRIDAY...UPPER WAVE MAKING ITS WAY EAST ACROSS THE
CANADIAN PRAIRIES WILL FINALLY KICK THE GREAT LAKES LOW TO THE EAST.
THIS WILL ALLOW AREA TEMPERATES TO MODERATE...ESPECIALLY FRIDAY...
AND SKIES TO CLEAR. THE CLEARING SHOULD ACTUALLY PRECLUDE THE
DEPARTURE OF THE SYSTEM TONIGHT AS DRY AIR AS BEEN MIXED INTO
PERSISTENT CLOUD DECK OVERHEAD AND IT HAS ATTAINED A DISTINCTLY
DIURNAL APPEARANCE. SO...EXPECT CLOUDS TO FADE FAIRLY RAPIDLY THIS
EVENING. THIS CLEARING WILL BE SHORT LIVED HOWEVER...AS CONVECTION
GETS GOING TO OUR WEST FRIDAY AFTERNOON AND STARTS SPILLING
EASTWARD.

FRIDAY NIGHT AND SATURDAY...A LOW LEVEL THERMAL GRADIENT WILL
DEVELOP FROM THE CENTRAL PLAINS...THROUGH SOUTHERN IA/NORTHERN MO...
BEFORE CURVING ACROSS SOUTHERN ILLINOIS. A SOUTHWESTERLY LOW LEVEL
JET IS EXPECTED TO HELP TRANSPORT RICH MOISTURE...PRECIPITABLE WATER
VALUES AROUND 2 INCHES...INTO THIS BOUNDARY FRIDAY EVENING.
INITIALLY THE LLJ WILL FOCUS IN THE VICINITY OF NE/IA/MO BORDER
AREA...AND IT IS EXPECTED TO VEER TOWARD SOUTHERN ILLINOIS BY
SATURDAY MORNING. THE MCS SHOULD DEVELOP ON THE NOSE OF THE LLJ...ALSO
SUPPORTED BY THE RIGHT REAR QUADRANT OF AN UPPER JET STREAK...AND
TRACK ALONG THE THERMAL GRADIENT TOWARD SOUTHERN ILLINOIS. WITH
THIS TRACK IN MIND...HAVE KEPT LIKELY POPS OVER THE SOUTHWEST
PORTION OF THE FORECAST AREA...WITH POPS TAPERING OFF AS YOU GO
NORTHEAST. SEVERE WEATHER DOES NOT LOOK LIKE TOO MUCH OF THREAT
WITH THIS SYSTEM...BUT HEAVY RAINFALL IS CERTAINLY POSSIBLE. IT
APPEARS THAT THE BULK OF THE PRECIPITATION SHOULD BE DONE BY
MIDDAY SATURDAY...SO HOPEFULLY IT WILL NOT PUT TOO MUCH OF A DAMPER ON
THE FOURTH OF JULY FESTIVITIES.

SATURDAY NIGHT INTO SUNDAY...QUIETER WEATHER IS EXPECTED AS NEUTRAL
FLOW DEVELOPS ALOFT AND HIGH PRESSURE BUILDS IN AT THE SURFACE.

LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...MODELS/ENSEMBLES IN
REASONABLE AGREEMENT THROUGH THE EXTENDED RANGE OF THE FORECAST. A
FAIRLY ZONAL FLOW IS EXPECTED TO BE IN PLACE ACROSS THE LOWER 48
STATES AT THE START OF THE PERIOD. THE FLOW SHOULD BECOME
INCREASINGLY AMPLIFIED AS THE WEEK PROGRESSES. INITIALLY A TROF WILL
CARVE OUT OVER THE EASTERN UNITED STATES...WITH A RIDGE BUILDING
ACROSS THE WESTERN STATES. THEN...THE RIDGE IS EXPECTED TO BUILD
EAST WITH TIME. HAVE MAINTAINED A DRY FORECAST THROUGH THE
PERIOD...WITH NO MAJOR WAVES/SYSTEMS AGREED UPON BY THE MODEL
CONSENSUS. SLIGHTLY BELOW NORMAL TEMPERATURES TO START THE PERIOD
WILL TREND TO NORMAL OR ABOVE AS THE STRONG RIDGE BUILDS IN.

BAK


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KILX 030200
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
900 PM CDT THU JUL 2 2009

.DISCUSSION...
ISSUED 900 PM CDT THU JUL 2 2009

CLOUD COVER IS DISSIPATING AS EXPECTED BUT SOME CLOUDS ARE STILL
AROUND...SO PARTLY CLOUDY SKIES FOR NOW LOOKS FINE. TEMPS SHOULD ALSO
FALL AS EXPECTED WITH WINDS BECOMING LIGHT. THEREFORE CURRENT
FORECAST LOOKS FINE AND NOT UPDATE REQUIRED AT THIS TIME.

AUTEN
&&

.AVIATION...
ISSUED 620 PM CDT THU JUL 2 2009

CYCLONIC FLOW FINALLY MOVING NORTHEAST AS THE UPPER LEVEL SYSTEM
LIFTS AWAY FROM THE AREA. CLOUDS STILL REMAIN AT ALL TAF SITES
WITH MAINLY BROKEN CIGS AT VFR LEVELS. SATELLITE LOOP INDICATES
CLOUDS ARE DIURNAL SO EXPECT THEM TO DISSIPATE AROUND SUNSET THIS
EVENING. THEN AS HIGH PRSS RIDGE MOVES TOWARD THE AREA FROM THE
WEST...SKIES WILL BECOME CLEAR AND WINDS WILL BECOME LIGHT. DO NOT
EXPECT ANY FOG FOR MORNING AS AIR IS QUITE DRY AT THE LOW LEVELS.
CIRRUS FROM APPROACHING SYSTEM FOR LATER THIS WEEK WILL ADVECT
INTO THE REGION TOMORROW ALONG WITH SOME SCATTERED CU WITH THE
HEATING OF THE DAY. WINDS WILL BECOME MORE WESTERLY AS THE RIDGE
MOVES CLOSER TO THE AREA TOMORROW.

AUTEN
&&

.PREV DISCUSSION...
ISSUED 259 PM CDT THU JUL 2 2009

PERSISTENT UPPER/SURFACE LOW CONTINUES TO SPIN OVER THE GREAT
LAKES/NORTHERN ONTARIO THIS AFTERNOON. CLOUDS CONTINUE TO SPILL OVER
THE FORECAST AREA IN THE WRAP AROUND MOISTURE ON THE BACK OF THIS
SYSTEM. THE DEPARTURE OF THIS SYSTEM TONIGHT/FRIDAY AND PASSAGE OF
A MCS FRIDAY NIGHT/EARLY SATURDAY ARE THE PRIMARY FORECAST CONCERNS
THIS PACKAGE AS THE REMAINDER OF THE FORECAST PERIOD LOOKS PRETTY
QUIET.

12Z MODELS ARE IN GOOD OVERALL AGREEMENT THROUGH THE PERIOD. THE
BIGGEST DIFFERENCE IN SENSIBLE WEATHER IS IN THE TRACK OF THE
EXPECTED MCS FRIDAY NIGHT/EARLY SATURDAY. THE ECMWF/CANADIAN REMAIN
FURTHER NORTH WITH THE QPF AXIS THAN THE GFS/NAM...DESPITE THE FACT
THAT THEY LARGELY AGREE ON THE LOW LEVEL THERMAL GRADIENT AND UPPER
DYNAMICS. GOING FORECAST AND CONCEPTUAL MODELS FAVOR THE GFS/NAM
SOLUTION AND WILL CONTINUE TO FAVOR THIS TRACK. GUIDANCE
TEMPERATURES GENERALLY CLOSE/REASONABLE. HOWEVER...TEMPERATURES
TONIGHT WILL BE LARGELY IMPACTED BY HOW QUICKLY SKIES CLEAR...WITH
TEMPERATURES FRIDAY NIGHT/SATURDAY BEING MODULATED BY THE EXPECTED
MCS.

SHORT TERM...TONIGHT THROUGH SUNDAY...

TONIGHT AND FRIDAY...UPPER WAVE MAKING ITS WAY EAST ACROSS THE
CANADIAN PRAIRIES WILL FINALLY KICK THE GREAT LAKES LOW TO THE EAST.
THIS WILL ALLOW AREA TEMPERATES TO MODERATE...ESPECIALLY FRIDAY...
AND SKIES TO CLEAR. THE CLEARING SHOULD ACTUALLY PRECLUDE THE
DEPARTURE OF THE SYSTEM TONIGHT AS DRY AIR AS BEEN MIXED INTO
PERSISTENT CLOUD DECK OVERHEAD AND IT HAS ATTAINED A DISTINCTLY
DIURNAL APPEARANCE. SO...EXPECT CLOUDS TO FADE FAIRLY RAPIDLY THIS
EVENING. THIS CLEARING WILL BE SHORT LIVED HOWEVER...AS CONVECTION
GETS GOING TO OUR WEST FRIDAY AFTERNOON AND STARTS SPILLING
EASTWARD.

FRIDAY NIGHT AND SATURDAY...A LOW LEVEL THERMAL GRADIENT WILL
DEVELOP FROM THE CENTRAL PLAINS...THROUGH SOUTHERN IA/NORTHERN MO...
BEFORE CURVING ACROSS SOUTHERN ILLINOIS. A SOUTHWESTERLY LOW LEVEL
JET IS EXPECTED TO HELP TRANSPORT RICH MOISTURE...PRECIPITABLE WATER
VALUES AROUND 2 INCHES...INTO THIS BOUNDARY FRIDAY EVENING.
INITIALLY THE LLJ WILL FOCUS IN THE VICINITY OF NE/IA/MO BORDER
AREA...AND IT IS EXPECTED TO VEER TOWARD SOUTHERN ILLINOIS BY
SATURDAY MORNING. THE MCS SHOULD DEVELOP ON THE NOSE OF THE LLJ...ALSO
SUPPORTED BY THE RIGHT REAR QUADRANT OF AN UPPER JET STREAK...AND
TRACK ALONG THE THERMAL GRADIENT TOWARD SOUTHERN ILLINOIS. WITH
THIS TRACK IN MIND...HAVE KEPT LIKELY POPS OVER THE SOUTHWEST
PORTION OF THE FORECAST AREA...WITH POPS TAPERING OFF AS YOU GO
NORTHEAST. SEVERE WEATHER DOES NOT LOOK LIKE TOO MUCH OF THREAT
WITH THIS SYSTEM...BUT HEAVY RAINFALL IS CERTAINLY POSSIBLE. IT
APPEARS THAT THE BULK OF THE PRECIPITATION SHOULD BE DONE BY
MIDDAY SATURDAY...SO HOPEFULLY IT WILL NOT PUT TOO MUCH OF A DAMPER ON
THE FOURTH OF JULY FESTIVITIES.

SATURDAY NIGHT INTO SUNDAY...QUIETER WEATHER IS EXPECTED AS NEUTRAL
FLOW DEVELOPS ALOFT AND HIGH PRESSURE BUILDS IN AT THE SURFACE.

LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...MODELS/ENSEMBLES IN
REASONABLE AGREEMENT THROUGH THE EXTENDED RANGE OF THE FORECAST. A
FAIRLY ZONAL FLOW IS EXPECTED TO BE IN PLACE ACROSS THE LOWER 48
STATES AT THE START OF THE PERIOD. THE FLOW SHOULD BECOME
INCREASINGLY AMPLIFIED AS THE WEEK PROGRESSES. INITIALLY A TROF WILL
CARVE OUT OVER THE EASTERN UNITED STATES...WITH A RIDGE BUILDING
ACROSS THE WESTERN STATES. THEN...THE RIDGE IS EXPECTED TO BUILD
EAST WITH TIME. HAVE MAINTAINED A DRY FORECAST THROUGH THE
PERIOD...WITH NO MAJOR WAVES/SYSTEMS AGREED UPON BY THE MODEL
CONSENSUS. SLIGHTLY BELOW NORMAL TEMPERATURES TO START THE PERIOD
WILL TREND TO NORMAL OR ABOVE AS THE STRONG RIDGE BUILDS IN.

BAK

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 030012
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
712 PM CDT THU JUL 2 2009

.DISCUSSION...
247 PM CDT

QUESTION ON THE MIND OF MOST IS WHAT DOES HOLIDAY WEEKEND LOOK.
ONLY A CHANCE OF SHOWERS AND THUNDERSTORMS FROM LATE FRIDAY NIGHT
INTO SATURDAY AND STILL LOOKS THREAT WILL BE MAINLY FROM FAR
SOUTHERN IA AND NORTHERN MO SOUTHEASTWARD ACROSS CENTRAL IL TO
SOUTHERN IN. HAVE SOME SLIGHT CHANCE AND CHANCE POPS EXTENDING INTO
PORTION OF N CENTRAL AND NE IL OVERNIGHT FRI AND FOR SAT
MORNING.

UPPER LOW OVER THE EASTERN GREAT LAKES CONTINUES TO VERY GRADUALLY
SHIFT EASTWARD ALLOWING MID/UPPER RIDGING TO BUILD OVER THE UPPER
MS VALLEY AND SHIFT TRAILING EDGE OF MAIN AREA OF STRATOCU DECK
ALSO EASTWARD...THOUGH EFFECTIVE CLEARING SLOWED BY DIURNAL
DEVELOPMENT ON PERIPHERY. AS SUN LOWERS CLEARING TO JUMP TO THE
EAST AS DIURNAL STRATOCU DISSIPATES.

DE-AMPLIFICATION OF PATTER TO CONTINUE OVERNIGHT THOUGH BROAD
UPPER MEAN TROF TO REMAIN OVER EASTERN CANADA AND NEW ENGLAND FRI
AS STRONG SHORT WAVE CURRENTLY OVER THE MANITOBA-ND BORDER DROPS
SE ACROSS THE N WOODS AND NORTHERN GREAT LAKES TONIGHT THRU SAT.

PUSHING OF LOW POPS A LITTLE FURTHER N ACROSS THE FA FOR LATE FRI
NIGHT AND SAT MORNING IS IN DEFERENCE TO LATEST SREF AND GFS
ENSEMBLE OUTPUTS BRUSHING N CENTRAL AN NE IL WITH LOWER END POPS
AND LIGHT QPFS AS SHORT WAVE TOPS BROAD ROCKIES/HI PLAINS RIDGE
FRI AND THEN DROPS SOUTHEASTWARD ACROSS THE MID MO AND MID MS
VALLEYS DURING FRI NIGHT AND EARLY SAT MORNING...CONTINUING TO THE
LOWER OH VALLEY BY EARLY SAT AFTERNOON. EXPECT AXIS OF QPF TO
EXTEND FROM FAR SOUTHERN IA/NORTHERN MO SE ACROSS W CENTRAL AND SE
IL TO THE LOWER OH RIVER SO CHANCE POPS ACROSS W AND S PORTIONS OF
LOCAL FA DECREASING TO SLIGHT CHANCE FURTHER N AND NE LATE FRI
NIGHT AND SAT MORNING...WITH LINGERING CHANCE POPS ACROSS FAR S
FOR SAT AFTERNOON TIL SHORT WAVE PULLS AWAY.

REST OF WEEKEND DRY WITH NW FLOW PERSISTING. THIS FLOW TO ALSO
KEEPS TEMPS WELL MODERATED WITH READINGS A BIT BELOW NORMS THO
THIS TIME OF YEAR THIS IS STILL COMFORTABLE. SURFACE RIDGE TO MOVE
OVER THE REGION ALLOWING LAKE BREEZE DEVELOPMENT. WITH SOUTHERN
LAKE MI WATER TEMPS NOW INTO THE MID AND UPPER 60S THIS WILL ALLOW
EVEN NEAR-LAKE AREAS TO REACH MID 70S.

NO REAL PROSPECTS FOR SIGNIFICANT THREAT OF RAIN MON THRU THU OF
NEXT WEEK AS COOL DRY NW FLOW PERSISTS.

TRS

&&

.AVIATION...

0000 UTC TAFS...A LARGE HIGH OVER THE EASTERN GREAT PLAINS WILL
MOVE INTO SOUTHERN ILLINOIS BY 18 UTC FRIDAY. WE EXPECT THE WIND
WILL DECREASE TO VARIABLE AROUND 4 KNOTS TONIGHT. THE LOW SURFACE
DEWPOINTS AS COMPARED TO THE TEMPERATURES INDICATE THE AIR IS
RATHER DRY. WE EXPECT LITTLE IF ANY FOG TONIGHT. THE SKY WILL
BECOME MOSTLY CLEAR. THE SMALL PRESSURE GRADIENT FRIDAY WILL
ALLOW A WEAK LAKE BREEZE TO DEVELOP FRIDAY AFTERNOON. THE HIGH
WILL MOVE INTO KENTUCKY FRIDAY EVENING. THIS LAKE BREEZE WILL
BE A NORTHEAST TO EAST WIND AT THE AIRPORTS IN NORTHEAST
ILLINOIS. WE WILL NOT ADD A PROBABILITY OF SHOWERS TO THIS SET OF
TAFS. THE CHANCE OF SHOWERS WILL BE IN ROCKFORD AFTER 00 UTC AND
THE REST OF THE TAFS AFTER 06 UTC SATURDAY MORNING. WE WILL
INCREASE THE CLOUDS FRIDAY AFTERNOON TO OVERCAST AT 25000 FEET.
THE CHANCE OF SHOWERS WILL BE A RESULT OF WARM AIR RETURNING TO
NORTHERN ILLINOIS WITH A SOUTH WIND.

WW

&&

.MARINE...
245 AM CDT

LARGE UPPER LOW PRESSURE AROUND GEORGIAN BAY WILL CONTINUE A SLOW
DRIFT EASTWARD TO WESTERN QUEBEC TONIGHT. WEAK HIGH PRESSURE WILL
THEN BUILD ACROSS THE WESTERN GREAT LAKES TONIGHT AND FRIDAY AND
ANCHOR THERE ACROSS THE UPPER GREAT LAKES THROUGH THE UPCOMING
WEEKEND. WEAK RIDGING WILL BRING LIGHT WINDS TO LAKE MICHIGAN
TONIGHT THROUGH THE WEEKEND.

RLB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KILX 022320
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
620 PM CDT THU JUL 2 2009

.DISCUSSION...
ISSUED 259 PM CDT THU JUL 2 2009

PERSISTENT UPPER/SURFACE LOW CONTINUES TO SPIN OVER THE GREAT
LAKES/NORTHERN ONTARIO THIS AFTERNOON. CLOUDS CONTINUE TO SPILL OVER
THE FORECAST AREA IN THE WRAP AROUND MOISTURE ON THE BACK OF THIS
SYSTEM. THE DEPARTURE OF THIS SYSTEM TONIGHT/FRIDAY AND PASSAGE OF
A MCS FRIDAY NIGHT/EARLY SATURDAY ARE THE PRIMARY FORECAST CONCERNS
THIS PACKAGE AS THE REMAINDER OF THE FORECAST PERIOD LOOKS PRETTY
QUIET.

12Z MODELS ARE IN GOOD OVERALL AGREEMENT THROUGH THE PERIOD. THE
BIGGEST DIFFERENCE IN SENSIBLE WEATHER IS IN THE TRACK OF THE
EXPECTED MCS FRIDAY NIGHT/EARLY SATURDAY. THE ECMWF/CANADIAN REMAIN
FURTHER NORTH WITH THE QPF AXIS THAN THE GFS/NAM...DESPITE THE FACT
THAT THEY LARGELY AGREE ON THE LOW LEVEL THERMAL GRADIENT AND UPPER
DYNAMICS. GOING FORECAST AND CONCEPTUAL MODELS FAVOR THE GFS/NAM
SOLUTION AND WILL CONTINUE TO FAVOR THIS TRACK. GUIDANCE
TEMPERATURES GENERALLY CLOSE/REASONABLE. HOWEVER...TEMPERATURES
TONIGHT WILL BE LARGELY IMPACTED BY HOW QUICKLY SKIES CLEAR...WITH
TEMPERATURES FRIDAY NIGHT/SATURDAY BEING MODULATED BY THE EXPECTED
MCS.

SHORT TERM...TONIGHT THROUGH SUNDAY...

TONIGHT AND FRIDAY...UPPER WAVE MAKING ITS WAY EAST ACROSS THE
CANADIAN PRAIRIES WILL FINALLY KICK THE GREAT LAKES LOW TO THE EAST.
THIS WILL ALLOW AREA TEMPERATES TO MODERATE...ESPECIALLY FRIDAY...
AND SKIES TO CLEAR. THE CLEARING SHOULD ACTUALLY PRECLUDE THE
DEPARTURE OF THE SYSTEM TONIGHT AS DRY AIR AS BEEN MIXED INTO
PERSISTENT CLOUD DECK OVERHEAD AND IT HAS ATTAINED A DISTINCTLY
DIURNAL APPEARANCE. SO...EXPECT CLOUDS TO FADE FAIRLY RAPIDLY THIS
EVENING. THIS CLEARING WILL BE SHORT LIVED HOWEVER...AS CONVECTION
GETS GOING TO OUR WEST FRIDAY AFTERNOON AND STARTS SPILLING
EASTWARD.

FRIDAY NIGHT AND SATURDAY...A LOW LEVEL THERMAL GRADIENT WILL
DEVELOP FROM THE CENTRAL PLAINS...THROUGH SOUTHERN IA/NORTHERN MO...
BEFORE CURVING ACROSS SOUTHERN ILLINOIS. A SOUTHWESTERLY LOW LEVEL
JET IS EXPECTED TO HELP TRANSPORT RICH MOISTURE...PRECIPITABLE WATER
VALUES AROUND 2 INCHES...INTO THIS BOUNDARY FRIDAY EVENING.
INITIALLY THE LLJ WILL FOCUS IN THE VICINITY OF NE/IA/MO BORDER
AREA...AND IT IS EXPECTED TO VEER TOWARD SOUTHERN ILLINOIS BY
SATURDAY MORNING. THE MCS SHOULD DEVELOP ON THE NOSE OF THE LLJ...ALSO
SUPPORTED BY THE RIGHT REAR QUADRANT OF AN UPPER JET STREAK...AND
TRACK ALONG THE THERMAL GRADIENT TOWARD SOUTHERN ILLINOIS. WITH
THIS TRACK IN MIND...HAVE KEPT LIKELY POPS OVER THE SOUTHWEST
PORTION OF THE FORECAST AREA...WITH POPS TAPERING OFF AS YOU GO
NORTHEAST. SEVERE WEATHER DOES NOT LOOK LIKE TOO MUCH OF THREAT
WITH THIS SYSTEM...BUT HEAVY RAINFALL IS CERTAINLY POSSIBLE. IT
APPEARS THAT THE BULK OF THE PRECIPITATION SHOULD BE DONE BY
MIDDAY SATURDAY...SO HOPEFULLY IT WILL NOT PUT TOO MUCH OF A DAMPER ON
THE FOURTH OF JULY FESTIVITIES.

SATURDAY NIGHT INTO SUNDAY...QUIETER WEATHER IS EXPECTED AS NEUTRAL
FLOW DEVELOPS ALOFT AND HIGH PRESSURE BUILDS IN AT THE SURFACE.

LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...MODELS/ENSEMBLES IN
REASONABLE AGREEMENT THROUGH THE EXTENDED RANGE OF THE FORECAST. A
FAIRLY ZONAL FLOW IS EXPECTED TO BE IN PLACE ACROSS THE LOWER 48
STATES AT THE START OF THE PERIOD. THE FLOW SHOULD BECOME
INCREASINGLY AMPLIFIED AS THE WEEK PROGRESSES. INITIALLY A TROF WILL
CARVE OUT OVER THE EASTERN UNITED STATES...WITH A RIDGE BUILDING
ACROSS THE WESTERN STATES. THEN...THE RIDGE IS EXPECTED TO BUILD
EAST WITH TIME. HAVE MAINTAINED A DRY FORECAST THROUGH THE
PERIOD...WITH NO MAJOR WAVES/SYSTEMS AGREED UPON BY THE MODEL
CONSENSUS. SLIGHTLY BELOW NORMAL TEMPERATURES TO START THE PERIOD
WILL TREND TO NORMAL OR ABOVE AS THE STRONG RIDGE BUILDS IN.

BAK
&&

.AVIATION...
ISSUED 620 PM CDT THU JUL 2 2009

CYCLONIC FLOW FINALLY MOVING NORTHEAST AS THE UPPER LEVEL SYSTEM
LIFTS AWAY FROM THE AREA. CLOUDS STILL REMAIN AT ALL TAF SITES
WITH MAINLY BROKEN CIGS AT VFR LEVELS. SATELLITE LOOP INDICATES
CLOUDS ARE DIURNAL SO EXPECT THEM TO DISSIPATE AROUND SUNSET THIS
EVENING. THEN AS HIGH PRSS RIDGE MOVES TOWARD THE AREA FROM THE
WEST...SKIES WILL BECOME CLEAR AND WINDS WILL BECOME LIGHT. DO NOT
EXPECT ANY FOG FOR MORNING AS AIR IS QUITE DRY AT THE LOW LEVELS.
CIRRUS FROM APPROACHING SYSTEM FOR LATER THIS WEEK WILL ADVECT
INTO THE REGION TOMORROW ALONG WITH SOME SCATTERED CU WITH THE
HEATING OF THE DAY. WINDS WILL BECOME MORE WESTERLY AS THE RIDGE
MOVES CLOSER TO THE AREA TOMORROW.

AUTEN
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KILX 021959
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
259 PM CDT THU JUL 2 2009

.DISCUSSION...
ISSUED 259 PM CDT THU JUL 2 2009

PERSISTENT UPPER/SURFACE LOW CONTINUES TO SPIN OVER THE GREAT
LAKES/NORTHERN ONTARIO THIS AFTERNOON. CLOUDS CONTINUE TO SPILL OVER
THE FORECAST AREA IN THE WRAP AROUND MOISTURE ON THE BACK OF THIS
SYSTEM. THE DEPARTURE OF THIS SYSTEM TONIGHT/FRIDAY AND PASSAGE OF
A MCS FRIDAY NIGHT/EARLY SATURDAY ARE THE PRIMARY FORECAST CONCERNS
THIS PACKAGE AS THE REMAINDER OF THE FORECAST PERIOD LOOKS PRETTY
QUIET.

12Z MODELS ARE IN GOOD OVERALL AGREEMENT THROUGH THE PERIOD. THE
BIGGEST DIFFERENCE IN SENSIBLE WEATHER IS IN THE TRACK OF THE
EXPECTED MCS FRIDAY NIGHT/EARLY SATURDAY. THE ECMWF/CANADIAN REMAIN
FURTHER NORTH WITH THE QPF AXIS THAN THE GFS/NAM...DESPITE THE FACT
THAT THEY LARGELY AGREE ON THE LOW LEVEL THERMAL GRADIENT AND UPPER
DYNAMICS. GOING FORECAST AND CONCEPTUAL MODELS FAVOR THE GFS/NAM
SOLUTION AND WILL CONTINUE TO FAVOR THIS TRACK. GUIDANCE
TEMPERATURES GENERALLY CLOSE/REASONABLE. HOWEVER...TEMPERATURES
TONIGHT WILL BE LARGELY IMPACTED BY HOW QUICKLY SKIES CLEAR...WITH
TEMPERATURES FRIDAY NIGHT/SATURDAY BEING MODULATED BY THE EXPECTED
MCS.

SHORT TERM...TONIGHT THROUGH SUNDAY...

TONIGHT AND FRIDAY...UPPER WAVE MAKING ITS WAY EAST ACROSS THE
CANADIAN PRAIRIES WILL FINALLY KICK THE GREAT LAKES LOW TO THE EAST.
THIS WILL ALLOW AREA TEMPERATES TO MODERATE...ESPECIALLY FRIDAY...
AND SKIES TO CLEAR. THE CLEARING SHOULD ACTUALLY PRECLUDE THE
DEPARTURE OF THE SYSTEM TONIGHT AS DRY AIR AS BEEN MIXED INTO
PERSISTENT CLOUD DECK OVERHEAD AND IT HAS ATTAINED A DISTINCTLY
DIURNAL APPEARANCE. SO...EXPECT CLOUDS TO FADE FAIRLY RAPIDLY THIS
EVENING. THIS CLEARING WILL BE SHORT LIVED HOWEVER...AS CONVECTION
GETS GOING TO OUR WEST FRIDAY AFTERNOON AND STARTS SPILLING
EASTWARD.

FRIDAY NIGHT AND SATURDAY...A LOW LEVEL THERMAL GRADIENT WILL
DEVELOP FROM THE CENTRAL PLAINS...THROUGH SOUTHERN IA/NORTHERN MO...
BEFORE CURVING ACROSS SOUTHERN ILLINOIS. A SOUTHWESTERLY LOW LEVEL
JET IS EXPECTED TO HELP TRANSPORT RICH MOISTURE...PRECIPITABLE WATER
VALUES AROUND 2 INCHES...INTO THIS BOUNDARY FRIDAY EVENING.
INITIALLY THE LLJ WILL FOCUS IN THE VICINITY OF NE/IA/MO BORDER
AREA...AND IT IS EXPECTED TO VEER TOWARD SOUTHERN ILLINOIS BY
SATURDAY MORNING. THE MCS SHOULD DEVELOP ON THE NOSE OF THE LLJ...ALSO
SUPPORTED BY THE RIGHT REAR QUADRANT OF AN UPPER JET STREAK...AND
TRACK ALONG THE THERMAL GRADIENT TOWARD SOUTHERN ILLINOIS. WITH
THIS TRACK IN MIND...HAVE KEPT LIKELY POPS OVER THE SOUTHWEST
PORTION OF THE FORECAST AREA...WITH POPS TAPERING OFF AS YOU GO
NORTHEAST. SEVERE WEATHER DOES NOT LOOK LIKE TOO MUCH OF THREAT
WITH THIS SYSTEM...BUT HEAVY RAINFALL IS CERTAINLY POSSIBLE. IT
APPEARS THAT THE BULK OF THE PRECIPITATION SHOULD BE DONE BY
MIDDAY SATURDAY...SO HOPEFULLY IT WILL NOT PUT TOO MUCH OF A DAMPER ON
THE FOURTH OF JULY FESTIVITIES.

SATURDAY NIGHT INTO SUNDAY...QUIETER WEATHER IS EXPECTED AS NEUTRAL
FLOW DEVELOPS ALOFT AND HIGH PRESSURE BUILDS IN AT THE SURFACE.

LONG TERM...SUNDAY NIGHT THROUGH THURSDAY...MODELS/ENSEMBLES IN
REASONABLE AGREEMENT THROUGH THE EXTENDED RANGE OF THE FORECAST. A
FAIRLY ZONAL FLOW IS EXPECTED TO BE IN PLACE ACROSS THE LOWER 48
STATES AT THE START OF THE PERIOD. THE FLOW SHOULD BECOME
INCREASINGLY AMPLIFIED AS THE WEEK PROGRESSES. INITIALLY A TROF WILL
CARVE OUT OVER THE EASTERN UNITED STATES...WITH A RIDGE BUILDING
ACROSS THE WESTERN STATES. THEN...THE RIDGE IS EXPECTED TO BUILD
EAST WITH TIME. HAVE MAINTAINED A DRY FORECAST THROUGH THE
PERIOD...WITH NO MAJOR WAVES/SYSTEMS AGREED UPON BY THE MODEL
CONSENSUS. SLIGHTLY BELOW NORMAL TEMPERATURES TO START THE PERIOD
WILL TREND TO NORMAL OR ABOVE AS THE STRONG RIDGE BUILDS IN.

BAK
&&

.AVIATION...
ISSUED 1255 PM CDT THU JUL 2 2009

MVFR TO VFR CEILINGS OF 2.5-5K FT SHOULD PREVAIL ACROSS THE
CENTRAL IL TERMINALS THIS AFTERNOON AND EARLY EVENING. DIURNALLY
ENHANCED CU/STRATOCU SHOULD SCATTERED OUT AROUND SUNSET BETWEEN
01-03Z (7-9 PM). LARGE 565 DM 500 MB LOW PRESURE OVER SE ONTARIO
PENISULA WILL CONTINUE TO WEAKEN AS IT LIFTS NE INTO THE ST
LAWRENCE SEAWAY OF SE CANADA BY 18Z/1 PM FRI. MEANWHILE WEAK 1018
MB HIGH PRESSURE OVER THE GREAT PLAINS WILL DRIFT OVER IL FRI
MORNING. WNW WINDS NEAR 10 KTS THIS AFTERNOON SHOULD BE LIGHT
TONIGHT AND FRI AS HIGH PRESSURE SETTLES IN. WITH LIGHT WINDS AND
SKIES CLEARING TONIGHT...COULD BE A LIGHT FOG WITH MVFR VSBYS OF
4 TO 5 MILES FROM 09Z TO 14Z (4-9 AM). CU RULE SHOWS SCATTERED
CUMULUS CLOUDS POSSIBLE LATER FRI MORNING/AFTERNOON ESPECIALLY IN
EASTERN IL AND HAVE BASES AROUND 4K FT.

HUETTL
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 021949
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
249 PM CDT THU JUL 2 2009

.DISCUSSION...
247 PM CDT

QUESTION ON THE MIND OF MOST IS WHAT DOES HOLIDAY WEEKEND LOOK.
ONLY A CHANCE OF SHOWERS AND THUNDERSTORMS FROM LATE FRIDAY NIGHT
INTO SATURDAY AND STILL LOOKS THREAT WILL BE MAINLY FROM FAR
SOUTHERN IA AND NORTHERN MO SOUTHEASTWARD ACROSS CENTRAL IL TO
SOUTHERN IN. HAVE SOME SLIGHT CHANCE AND CHANCE POPS EXTENDING INTO
PORTION OF N CENTRAL AND NE IL OVERNIGHT FRI AND FOR SAT
MORNING.

UPPER LOW OVER THE EASTERN GREAT LAKES CONTINUES TO VERY GRADUALLY
SHIFT EASTWARD ALLOWING MID/UPPER RIDGING TO BUILD OVER THE UPPER
MS VALLEY AND SHIFT TRAILING EDGE OF MAIN AREA OF STRATOCU DECK
ALSO EASTWARD...THOUGH EFFECTIVE CLEARING SLOWED BY DIURNAL
DEVELOPMENT ON PERIPHERY. AS SUN LOWERS CLEARING TO JUMP TO THE
EAST AS DIURNAL STRATOCU DISSIPATES.

DE-AMPLIFICATION OF PATTER TO CONTINUE OVERNIGHT THOUGH BROAD
UPPER MEAN TROF TO REMAIN OVER EASTERN CANADA AND NEW ENGLAND FRI
AS STRONG SHORT WAVE CURRENTLY OVER THE MANITOBA-ND BORDER DROPS
SE ACROSS THE N WOODS AND NORTHERN GREAT LAKES TONIGHT THRU SAT.

PUSHING OF LOW POPS A LITTLE FURTHER N ACROSS THE FA FOR LATE FRI
NIGHT AND SAT MORNING IS IN DEFERENCE TO LATEST SREF AND GFS
ENSEMBLE OUTPUTS BRUSHING N CENTRAL AN NE IL WITH LOWER END POPS
AND LIGHT QPFS AS SHORT WAVE TOPS BROAD ROCKIES/HI PLAINS RIDGE
FRI AND THEN DROPS SOUTHEASTWARD ACROSS THE MID MO AND MID MS
VALLEYS DURING FRI NIGHT AND EARLY SAT MORNING...CONTINUING TO THE
LOWER OH VALLEY BY EARLY SAT AFTERNOON. EXPECT AXIS OF QPF TO
EXTEND FROM FAR SOUTHERN IA/NORTHERN MO SE ACROSS W CENTRAL AND SE
IL TO THE LOWER OH RIVER SO CHANCE POPS ACROSS W AND S PORTIONS OF
LOCAL FA DECREASING TO SLIGHT CHANCE FURTHER N AND NE LATE FRI
NIGHT AND SAT MORNING...WITH LINGERING CHANCE POPS ACROSS FAR S
FOR SAT AFTERNOON TIL SHORT WAVE PULLS AWAY.

REST OF WEEKEND DRY WITH NW FLOW PERSISTING. THIS FLOW TO ALSO
KEEPS TEMPS WELL MODERATED WITH READINGS A BIT BELOW NORMS THO
THIS TIME OF YEAR THIS IS STILL COMFORTABLE. SURFACE RIDGE TO MOVE
OVER THE REGION ALLOWING LAKE BREEZE DEVELOPMENT. WITH SOUTHERN
LAKE MI WATER TEMPS NOW INTO THE MID AND UPPER 60S THIS WILL ALLOW
EVEN NEAR-LAKE AREAS TO REACH MID 70S.

NO REAL PROSPECTS FOR SIGNIFICANT THREAT OF RAIN MON THRU THU OF
NEXT WEEK AS COOL DRY NW FLOW PERSISTS.

TRS

&&

.AVIATION...

1800 UTC TAFS...UPR LOW NEAR LAKE ONTARIO SHUD CONTINUE TO SLOWLY
SHIFT EAST NEXT 24 HRS AS UPR RIDGE IN PLAINS STRENGTHENS INTO THE
UPR MS VLY. EXPECT CONTD LIGHT TO MDT NW WINDS INTERRUPTED BY PSBL
LAKE BREEZES ALLOWED BY RATHER WEAK SFC FLOW. THIS DEPENDENT ON
TEMP DIFFERENTIAL BTWN LAKE AND LAND. SOME BREAKS IN CLOUD COVER
SHUD PERMIT HIGHS TO PUSH INTO THE MID 70S. THIS MAY BE ENUF TO
INDUCE A WEAK LAKE BREEZE THIS AFTN. MODELS ARE HINTING AT SUCH
BUT WEAK TEMP DIFFERENTIAL MAY NOT PERMIT IT. MVFR DECK IN MAIN
CLOUD MASS AROUND THE UPR LOW INDICATING MVFR IN NRN WI. HEATING
MAY LIFT DECK ABOVE 3K BY THE TIME IT ROTATES ACROSS TERMINALS. SC
DECK LIKELY TO MOVE ON OR BREAK UP LATE IN THE AFTN...FOLLOWED BY
CLEARING SKIES AND CALMING WINDS OVERNIGHT. WINDS ONLY TO PICK UP
AGAIN FROM THE NW FRIDAY WITH PSBL LAKE BREEZE AGAIN IN THE AFTN.
CI DECK APPROACHING FRIDAY AS WAA AHEAD OF THE NEXT WAVE SPREADS
MSTR INTO THE FAR UPR LVLS.

RLB

&&

.MARINE...
245 AM CDT

LARGE UPPER LOW PRESSURE AROUND GEORGIAN BAY WILL CONTINUE A SLOW
DRIFT EASTWARD TO WESTERN QUEBEC TONIGHT. WEAK HIGH PRESSURE WILL
THEN BUILD ACROSS THE WESTERN GREAT LAKES TONIGHT AND FRIDAY AND
ANCHOR THERE ACROSS THE UPPER GREAT LAKES THROUGH THE UPCOMING
WEEKEND. WEAK RIDGING WILL BRING LIGHT WINDS TO LAKE MICHIGAN
TONIGHT THROUGH THE WEEKEND.

RLB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KLOT 021809
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
109 PM CDT THU JUL 2 2009

.DISCUSSION...
1054 AM CDT

ONLY VERY MINOR TWEAKS TO FORECAST GRID ELEMENTS FOR REMAINDER OF
TODAY. RATHER LARGE GASH IN STRATOCU DECK THAT EXISTED OVER MUCH
OF THE LOCAL FORECAST AREA EARLY THIS MORNING HAS ALREADY FILLED
IN PRETTY WELL DIURNALLY WITH A FEW HOURS OF SURFACE HEATING AND
COOL CYCLONIC FLOW.

UPPER LOW OVER THE EASTERN GREAT LAKES TO CONTINUE TO VERY GRADUALLY
SHIFT EASTWARD ALLOWING MID/UPPER RIDGING TO BUILD OVER THE UPPER
MS VALLEY AND SHIFT TRAILING EDGE OF MAIN AREA OF STRATOCU DECK
ALSO EASTWARD.

EXPECT THIS GRADUAL CLEARING TO SHIFT INTO WESTERN PORTIONS OF
THE FA DURING THE DAY. BRAKES IN CLOUDS GENERALLY DECREASE IN
CLOUD COVER AND 850 HPA TEMPS WARMING 2-3 DEG C BETWEEN 02/12Z AND
03/00Z SHOULD ALLOW SURFACE TEMPS TO REACH LOWER 70S
NORTHEAST FA...AND MID TO UPPER 70S SOUTHWEST. WEAK SYNOPTIC LOW
LEVEL FLOW WITH SURFACE RIDGE PUSHING ACROSS WI LIKELY TO ALLOW
A LAKE BREEZE TO DEVELOP THOUGH WILL BE WEAK AS LAND-AIR TEMP
DIFFERENTIAL WILL NOT BE THAT GREAT NOW THAT SOUTHERN LAKE MI
SURFACE WATER HAS WARMED INTO THE MID AND UPPER 60S DUE TO VERY
WARM PD THE REGION EXPERIENCED FOR A PORTION OF LAST WEEK.

TRS

&&

.AVIATION...

1800 UTC TAFS...UPR LOW NEAR LAKE ONTARIO SHUD CONTINUE TO SLOWLY
SHIFT EAST NEXT 24 HRS AS UPR RIDGE IN PLAINS STRENGTHENS INTO THE
UPR MS VLY. EXPECT CONTD LIGHT TO MDT NW WINDS INTERRUPTED BY PSBL
LAKE BREEZES ALLOWED BY RATHER WEAK SFC FLOW. THIS DEPENDENT ON
TEMP DIFFERENTIAL BTWN LAKE AND LAND. SOME BREAKS IN CLOUD COVER
SHUD PERMIT HIGHS TO PUSH INTO THE MID 70S. THIS MAY BE ENUF TO
INDUCE A WEAK LAKE BREEZE THIS AFTN. MODELS ARE HINTING AT SUCH
BUT WEAK TEMP DIFFERENTIAL MAY NOT PERMIT IT. MVFR DECK IN MAIN
CLOUD MASS AROUND THE UPR LOW INDICATING MVFR IN NRN WI. HEATING
MAY LIFT DECK ABOVE 3K BY THE TIME IT ROTATES ACROSS TERMINALS. SC
DECK LIKELY TO MOVE ON OR BREAK UP LATE IN THE AFTN...FOLLOWED BY
CLEARING SKIES AND CALMING WINDS OVERNIGHT. WINDS ONLY TO PICK UP
AGAIN FROM THE NW FRIDAY WITH PSBL LAKE BREEZE AGAIN IN THE AFTN.
CI DECK APPROACHING FRIDAY AS WAA AHEAD OF THE NEXT WAVE SPREADS
MSTR INTO THE FAR UPR LVLS.

RLB

&&

.MARINE...
245 AM CDT

LARGE UPPER LOW PRESSURE AROUND GEORGIAN BAY WILL CONTINUE A SLOW
DRIFT EASTWARD TO WESTERN QUEBEC TONIGHT. WEAK HIGH PRESSURE WILL
THEN BUILD ACROSS THE WESTERN GREAT LAKES TONIGHT AND FRIDAY AND
ANCHOR THERE ACROSS THE UPPER GREAT LAKES THROUGH THE UPCOMING
WEEKEND. WEAK RIDGING WILL BRING LIGHT WINDS TO LAKE MICHIGAN
TONIGHT THROUGH THE WEEKEND.

RLB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KILX 021756
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1256 PM CDT THU JUL 2 2009

.DISCUSSION...
ISSUED 1045 AM CDT THU JUL 2 2009

FORECAST LOOKS ON TRACK TODAY AND ONLY MINOR UPDATES TO THE HOURLY
WEATHER PARAMETERS LIKE TEMPERATURES...DEWPOINTS AND WINDS. MOSTLY
CLOUDY SKIES WILL BECOME PARTLY TO MOSTLY SUNNY LATER TODAY WITH
MORE SUNSHINE ACRSOS WESTERN IL. NOT QUITE AS COOL AS YESTERDAY
DUE TO MORE SUNSHINE APPEARING DURING THE AFTERNOON...WITH HIGHS
IN THE MID TO UPPER 70S. NEAR 80F FROM JACKSONVILLE SW. NW WINDS 5
TO 10 MPH.

AT LATE MORNING A 564 DM 500 MB LOW PRESSURE WAS OVER LAKE HURON
AND LAKE ERIE ABOUT WHERE IT WAS YESTERDAY BUT 5 DM WEAKER. IL
STILL CAUGHT UP IN ITS CYCLONIC CIRCULATION AND GENERATING PARTLY
CLOUDY TO OVERCAST LOW CLOUDS OVER MUCH OF IL. 10 AM TEMPERATURES
WERE 65 TO 70F WITH DEWPOINTS IN THE MID TO UPPER 50S AND NW WINDS
5 TO 10 MPH.

SHORT RANGE MODELS SHOW THE LARGE UPPER LEVEL LOW PRESSURE WILL
CONTINUE TO SLOWLY WEAKEN AS IT STARTS TO LIFT NE INTO THE ST
LAWRENCE VALLEY OF SE CANADA TONIGHT. MEANWHILE WEAK 1018 MB HIGH
PRESSURE OVER THE GREAT PLAINS NEARING MO AND IA WILL DRIFT INTO
IL TONIGHT AND HELP DECREASE CLOUDS LATER TODAY AND THIS EVENING.
850 MB TEMPS WARM A FEW DEGREES TODAY SO HIGHS A BIT MILDER IN THE
MID TO UPPER 70S AND NEAR 80F FROM JACKSONVILLE SW. STILL BELOW
NORMAL HIGHS FOR EARLY JULY IN THE MID TO UPPER 80S.

HUETTL

&&

.AVIATION...
ISSUED 1255 PM CDT THU JUL 2 2009

MVFR TO VFR CEILINGS OF 2.5-5K FT SHOULD PREVAIL ACROSS THE
CENTRAL IL TERMINALS THIS AFTERNOON AND EARLY EVENING. DIURNALLY
ENHANCED CU/STRATOCU SHOULD SCATTERED OUT AROUND SUNSET BETWEEN
01-03Z (7-9 PM). LARGE 565 DM 500 MB LOW PRESURE OVER SE ONTARIO
PENISULA WILL CONTINUE TO WEAKEN AS IT LIFTS NE INTO THE ST
LAWRENCE SEAWAY OF SE CANADA BY 18Z/1 PM FRI. MEANWHILE WEAK 1018
MB HIGH PRESSURE OVER THE GREAT PLAINS WILL DRIFT OVER IL FRI
MORNING. WNW WINDS NEAR 10 KTS THIS AFTERNOON SHOULD BE LIGHT
TONIGHT AND FRI AS HIGH PRESSURE SETTLES IN. WITH LIGHT WINDS AND
SKIES CLEARING TONIGHT...COULD BE A LIGHT FOG WITH MVFR VSBYS OF
4 TO 5 MILES FROM 09Z TO 14Z (4-9 AM). CU RULE SHOWS SCATTERED
CUMULUS CLOUDS POSSIBLE LATER FRI MORNING/AFTERNOON ESPECIALLY IN
EASTERN IL AND HAVE BASES AROUND 4K FT.

HUETTL

&&

.PREV DISCUSSION...
ISSUED 255 AM CDT THU JUL 2 2009

LITTLE CHANGE IN SFC OR UPPER AIR PATTERN FROM LAST COUPLE MORNINGS.
DEEP CUTOFF LOW CONTINUES TO SPIN OVER THE ERN GRT LAKES AND SLOWLY
FILL...00Z ANALYSIS HAD LARGE AREA OF +30M HEIGHT RISES NEAR AND
SOUTH OF THE LOW. LEAD SHORTWAVE TOPPING UPPER RIDGE OVER THE
ROCKIES AND SPARKING A CONVECTIVE COMPLEX IN THE CENTRAL PLAINS.
CYCLONIC FLOW AND STRATUS DECK STILL AFFECTING MOST OF THE CWA...BUT
SOME BREAKS SHOWING UP ACROSS NRN IL...WITH TEMPS IN THESE LOCATIONS
QUICKLY DROPPING OFF INTO THE MID 50S. OTHERWISE INSULATING EFFECT
OF CLOUDS KEEPING MOST AREAS IN LOW/MID 60S DESPITE VERY COOL EARLY
JULY AIRMASS OVERHEAD. MAIN FORECAST ISSUES ARE CLOUD TRENDS AND
IMPACT ON TEMPS TODAY...AND INCREASING POTENTIAL FOR UNSETTLED
WEATHER FRIDAY NIGHT INTO SATURDAY.

SHORT TERM...TODAY THROUGH SATURDAY
UPPER LOW BEGINS TO LOSE ITS INFLUENCE ON CENTRAL IL TODAY AS IT
FILLS AND LIFTS EAST. MEAN LAYER RH PROGS OFF NAM/GFS SHOW DEEPER
MOISTURE PUSHING EAST THROUGH THE DAY ALLOWING MORE BREAKS FOR
SUN...THOUGH STEEP LLVL LAPSE RATES AND CYCLONIC FLOW WILL PROMOTE
CU/SC DEVELOPMENT FOR MOSTLY CLOUDY SKIES. TRENDED TOWARDS LOWER
GUIDANCE HIGHS OF MID 70S NE TO AROUND 80 IN THE FAR SW. TONIGHT
WITH CLEARING SKIES AND LIGHT WINDS...SEASONABLY COOL LOWS AROUND 60
ARE EXPECTED. UPPER LEVEL HEIGHTS RISE ON FRIDAY AND MORE ABUNDANT
SUNSHINE SHOULD HELP BOOST TEMPS BACK TO NEAR NORMAL...IN THE
LOW/MID 80S.

CLOUDS WILL BE ON THE INCREASE LATE FRIDAY AS A CONVECTIVE COMPLEX
FROM THE PLAINS TRACKS EAST. MID-LEVEL WAVE WILL ACT ON BAROCLINIC
ZONE TO OUR SOUTHWEST AND RETURN FLOW OF MOISTURE UP FROM THE GULF.
LATEST RUN OF NAM/GFS IN BETTER AGREEMENT BRINGING SOME INGREDIENTS
TOGETHER FOR MODERATE RAINS OF 1+ INCHES FRIDAY NIGHT INTO EARLY
SATURDAY FOR THE SOUTHERN THIRD TO HALF OF THE CWA. LLVL THETA-E
ADVECTION AND MOISTURE CONVERGENCE RAMP UP FRIDAY NIGHT...WHILE GOOD
CONVERGENCE SETS UP ALONG 850 MB FRONT WHICH TRACKS NORTH TOWARDS
CENTRAL IL. UPPER LEVEL JET STREAK DIVING THROUGH THE GRT LAKES ALSO
AIDS IN LARGE-SCALE UPPER DIVERGENCE. HAVE BUMPED POPS TO LIKELY
ACROSS THE SOUTH AND TRIED TO FOCUS WITHIN THE 06-18Z SAT TIMEFRAME.
NEWLY ARRIVED ECMWF SHIFTS MAIN PRECIP AXIS FARTHER NORTH AND
LINGERS THROUGH SATURDAY...BUT THIS SEEMS TOO FAR NORTH GIVEN THE
PLACEMENT OF LLVL MOISTURE AND FORCING. SOME ELEVATED INSTABILITY
WARRANTS KEEPING THUNDER MENTION IN...THOUGH THIS MAY BE MARGINAL
NORTH OF I-74. STILL SOME UNCERTAINTY WITH TIMING OF SYSTEM...BUT
DID LOWER SAT AFTERNOON POPS TO LOW CHC BASED ON GFS/NAM BLEND.

LONG TERM...SUNDAY THROUGH WEDNESDAY
WITH FRONT WELL SOUTH OF THE AREA AND NORTHWEST FLOW ACROSS THE
UPPER MIDWEST...EXPECT A PERIOD OF GENERALLY DRY AND SEASONABLE
CONDITIONS. LARGE UPPER RIDGE FROM THE SOUTHWEST APPROACHES BY
MID-WEEK...SO A RETURN TO MORE SUMMERTIME HEAT/HUMIDITY MAY BE ON
TAP FOR THE MIDDLE AND END OF THE WEEK.

25


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 021555
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1055 AM CDT THU JUL 2 2009

.DISCUSSION...
1054 AM CDT

ONLY VERY MINOR TWEAKS TO FORECAST GRID ELEMENTS FOR REMAINDER OF
TODAY. RATHER LARGE GASH IN STRATOCU DECK THAT EXISTED OVER MUCH
OF THE LOCAL FORECAST AREA EARLY THIS MORNING HAS ALREADY FILLED
IN PRETTY WELL DIURNALLY WITH A FEW HOURS OF SURFACE HEATING AND
COOL CYCLONIC FLOW.

UPPER LOW OVER THE EASTERN GREAT LAKES TO CONTINUE TO VERY GRADUALLY
SHIFT EASTWARD ALLOWING MID/UPPER RIDGING TO BUILD OVER THE UPPER
MS VALLEY AND SHIFT TRAILING EDGE OF MAIN AREA OF STRATOCU DECK
ALSO EASTWARD.

EXPECT THIS GRADUAL CLEARING TO SHIFT INTO WESTERN PORTIONS OF
THE FA DURING THE DAY. BRAKES IN CLOUDS GENERALLY DECREASE IN
CLOUD COVER AND 850 HPA TEMPS WARMING 2-3 DEG C BETWEEN 02/12Z AND
03/00Z SHOULD ALLOW SURFACE TEMPS TO REACH LOWER 70S
NORTHEAST FA...AND MID TO UPPER 70S SOUTHWEST. WEAK SYNOPTIC LOW
LEVEL FLOW WITH SURFACE RIDGE PUSHING ACROSS WI LIKELY TO ALLOW
A LAKE BREEZE TO DEVELOP THOUGH WILL BE WEAK AS LAND-AIR TEMP
DIFFERENTIAL WILL NOT BE THAT GREAT NOW THAT SOUTHERN LAKE MI
SURFACE WATER HAS WARMED INTO THE MID AND UPPER 60S DUE TO VERY
WARM PD THE REGION EXPERIENCED FOR A PORTION OF LAST WEEK.

TRS

&&

.PREV DISCUSSION...

247 AM...TEMPS BEGIN TO MODERATE TODAY WARMING INTO THE LOWER 80S
FRIDAY...WITH A CHANCE OF THUNDERSTORMS FRIDAY NIGHT INTO SATURDAY.

UPPER LOW OVER THE EASTERN LAKES FINALLY BEGINS TO MOVE EAST
TONIGHT INTO FRIDAY. ONE MORE WEAK WAVE ROTATES SOUTH ACROSS
WESTERN MI TODAY WHICH COULD PRODUCE A SHOWER OVER THE LAKE INTO
NORTHERN INDIANA BUT EXPECT MUCH OF THE CWA TO REMAIN DRY. QUITE A
FEW BREAKS IN THE CLOUDS HAVE DEVELOPED OVERNIGHT. EXPECT THESE TO
FILL IN DURING THE MORNING HRS BUT BY MID/LATE AFTERNOON CLOUDS
SHOULD BEGIN TO SCATTER WITH SUNSHINE ALLOWING TEMPS TO REACH THE
MID 70S BY LATE AFTERNOON.

SKIES MOSTLY CLEAR TONIGHT BUT WITH WAA IN PROGRESS EXPECT TEMPS
TO DROP QUICKLY IN THE EVENING THEN HOLD STEADY THRU THE NIGHT.
FRIDAY SHOULD START MAINLY SUNNY WITH INCREASING HIGH CLOUDS
LATER IN THE DAY. GUIDANCE STILL PUSHING HIGHS INTO THE LOWER 80S
WHICH SEEMS REASONABLE...BUT A LAKE BREEZE MAY KEEP THE LAKE SHORE
AREAS A FEW DEGREES COOLER.

FRIDAY NIGHT INTO SATURDAY IS BECOMING MORE UNCERTAIN WITH EACH
NEW MODEL RUN. IT APPEARED 24 HRS AGO THAT A COMPLEX OF TS WOULD
MOVE FROM THE PLAINS TO THE OH VALLEY...WELL SOUTH OF NORTHERN IL
PERHAPS JUST CLIPPING THE SOUTHERN CWA. MODELS CONTINUE TO TRACK
THIS SYSTEM A LITTLE FURTHER NORTH. THE 00Z CANADIAN THIS MORNING
APPEARED TO BE AN OUTLIER AS IT TRACKED THIS SYSTEM RIGHT ACROSS
NORTHERN IL FRIDAY NIGHT...BUT THE NEW 00Z ECMWF IS FURTHER NORTH
WHILE THE LATEST SREF...03Z...SUPPORTS A FURTHER SOUTH TRACK.
THICKNESS PATTERNS WOULD ALL SUGGEST A SOUTHEAST MOVEMENT...OR A
TURN TO THE SOUTHEAST...BUT THAT TURN CONTINUES TO OCCUR FURTHER
NORTH. HAVE MOVED LOW CHANCE POPS FURTHER NORTH FRIDAY NIGHT...
GENERALLY ALONG A ROCHELLE TO RENSSELAER LINE. CONFIDENCE IS NOT
TOO HIGH GIVEN THE CONTINUAL SHIFTING IN THE MODELS BUT WITH THE
UPPER LOW OVER THE LAKES DEPARTING...THE UPPER RIDGE OVER THE
PLAINS MAY BE ABLE TOO BUILD FARTHER NORTHEAST...THUS SHIFTING THE
PRECIP FARTHER NORTHEAST AS WELL. EXPECT CHANGES TO THIS PERIOD OF
THE FORECAST AS LATER RUNS HOPEFULLY PIN DOWN BETTER CONSISTENCY
AND LOCATION. LINGERING PRECIP CHANCES SATURDAY INTO SATURDAY
EVENING DEPENDENT ON HOW FAR NORTH THIS SYSTEM TRACKS. NO CHANGES
AFTER SATURDAY. CMS

&&

.AVIATION...
DISCUSSION REGARDING 12Z TAFS...
610 AM CDT

LARGE AND PERSISTENT UPR LVL LOW NR LK HURON IS FCST TO SLOWLY SHIFT
EWD TODAY.  SATLT TRENDS SHOW LOW RANGE VFR STRATO CU DECK ERODING A
BIT ALONG WRN EDGE OF CIRCULATION.  LARGE HOLE IN OVC HAS DVLPD OVR
SRN WI-NRN IL.  EXPECT THIS IS TEMPORARY AND WILL MAINTAIN A BKN VFR
CIG IN FCST THRU MID MORNING.  ALSO...ENUF COLD AIR ALOFT STILL OVR
RGN TO DVLP INSTABILITY CU LATE MRNG-ERLY AFTN...ESPECIALLY IN AREAS
WHERE SUNSHINE DOES PERSIST INTO THE MID MORNING HRS.

BY THIS EVENING HOWEVER...EXPECT CLOUD BASES TO LIFT AND SCT OUT
AS SFC COOLS.  EXTENSION OF WEAK HI PRESSURE RIDGE TO SHIFT EWD TO
MID/UPR MS VLY BY 00Z AND GRADIENT WILL BE VERY WEAK. AS A
RESULT...NWLY-NNWLY SFC FLOW TO DIMINISH TO BLO 10 KTS BY 00Z...THEN
DROP OFF TO VRBL UNDER 5 KTS BY LATE EVENING AS SKIES CLR AND
CONDITIONS REMAIN VFR THROUGH THURSDAY NIGHT.

MERZLOCK

&&

.MARINE...
245 AM CDT

A LARGE AREA OF LOW PRESSURE NEAR GEORGIAN BAY WILL SLOWLY DRIFT
EASTWARD TO WESTERN QUEBEC TODAY AND TONIGHT. A WEAK HIGH PRESSURE
RIDGE WILL THEN BUILD ACROSS THE WESTERN GREAT LAKES TONIGHT AND
FRIDAY AND REMAIN IN PLACE ACROSS THE UPPER GREAT LAKES THROUGH THE
UPCOMING WEEKEND.

THIS WEAK RIDGE WILL BRING LIGHT WINDS TO LAKE MICHIGAN
THURSDAY NIGHT THROUGH MUCH OF THE UPCOMING WEEKEND.

MERZLOCK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KILX 021543
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1043 AM CDT THU JUL 2 2009

.DISCUSSION...
ISSUED 1045 AM CDT THU JUL 2 2009

FORECAST LOOKS ON TRACK TODAY AND ONLY MINOR UPDATES TO THE HOURLY
WEATHER PARAMETERS LIKE TEMPERATURES...DEWPOINTS AND WINDS. MOSTLY
CLOUDY SKIES WILL BECOME PARTLY TO MOSTLY SUNNY LATER TODAY WITH
MORE SUNSHINE ACRSOS WESTERN IL. NOT QUITE AS COOL AS YESTERDAY
DUE TO MORE SUNSHINE APPEARING DURING THE AFTERNOON...WITH HIGHS
IN THE MID TO UPPER 70S. NEAR 80F FROM JACKSONVILLE SW. NW WINDS 5
TO 10 MPH.

AT LATE MORNING A 564 DM 500 MB LOW PRESSURE WAS OVER LAKE HURON
AND LAKE ERIE ABOUT WHERE IT WAS YESTERDAY BUT 5 DM WEAKER. IL
STILL CAUGHT UP IN ITS CYCLONIC CIRCULATION AND GENERATING PARTLY
CLOUDY TO OVERCAST LOW CLOUDS OVER MUCH OF IL. 10 AM TEMPERATURES
WERE 65 TO 70F WITH DEWPOINTS IN THE MID TO UPPER 50S AND NW WINDS
5 TO 10 MPH.

SHORT RANGE MODELS SHOW THE LARGE UPPER LEVEL LOW PRESSURE WILL
CONTINUE TO SLOWLY WEAKEN AS IT STARTS TO LIFT NE INTO THE ST
LAWRENCE VALLEY OF SE CANADA TONIGHT. MEANWHILE WEAK 1018 MB HIGH
PRESSURE OVER THE GREAT PLAINS NEARING MO AND IA WILL DRIFT INTO
IL TONIGHT AND HELP DECREASE CLOUDS LATER TODAY AND THIS EVENING.
850 MB TEMPS WARM A FEW DEGREES TODAY SO HIGHS A BIT MILDER IN THE
MID TO UPPER 70S AND NEAR 80F FROM JACKSONVILLE SW. STILL BELOW
NORMAL HIGHS FOR EARLY JULY IN THE MID TO UPPER 80S.

HUETTL

&&

.AVIATION...
ISSUED 615 AM CDT THU JUL 2 2009

MORE HOLES ARE SHOWING UP IN THE STRATOCU FIELD THIS MORN THAN PREV
MORNS...HWVR WITH THE DEEP LYR CYCLONIC FLOW CONTG...EXPECT ANY GAPS
TO BE FILLED BACK IN BY MID MORN. A FEW CLDS IN THE 2500-3000 FT
RANGE HAVE BEEN DRIFTING AROUND...BUT OVERALL CIGS TDY SHOULD BE
VFR IN THE 3K-4K FT RANGE. SOME ISOLD VRY LGT RAIN SHOWING UP ON
RADAR EARLY THIS MORN NE OF A GBG-AAA-MTO LN WITH LTL AFFECT ON
CIGS/VSBYS. MAY INCL SOME -RA BEF 15Z TDY DEPENDING ON LAST MIN
RADAR TRENDS. AS THE ERN GREAT LAKES UPR LOW FINALLY EXITS THE
REGION LATER TDY...LOW LVL FLOW SHOULD BACK TO WLY AND ALLOW AN
EROSION OF THE LOW CLDS W TO E IN THE 00Z-03Z FRI TIME FRAME.

04
&&

.PREV DISCUSSION...
ISSUED 255 AM CDT THU JUL 2 2009

LITTLE CHANGE IN SFC OR UPPER AIR PATTERN FROM LAST COUPLE MORNINGS.
DEEP CUTOFF LOW CONTINUES TO SPIN OVER THE ERN GRT LAKES AND SLOWLY
FILL...00Z ANALYSIS HAD LARGE AREA OF +30M HEIGHT RISES NEAR AND
SOUTH OF THE LOW. LEAD SHORTWAVE TOPPING UPPER RIDGE OVER THE
ROCKIES AND SPARKING A CONVECTIVE COMPLEX IN THE CENTRAL PLAINS.
CYCLONIC FLOW AND STRATUS DECK STILL AFFECTING MOST OF THE CWA...BUT
SOME BREAKS SHOWING UP ACROSS NRN IL...WITH TEMPS IN THESE LOCATIONS
QUICKLY DROPPING OFF INTO THE MID 50S. OTHERWISE INSULATING EFFECT
OF CLOUDS KEEPING MOST AREAS IN LOW/MID 60S DESPITE VERY COOL EARLY
JULY AIRMASS OVERHEAD. MAIN FORECAST ISSUES ARE CLOUD TRENDS AND
IMPACT ON TEMPS TODAY...AND INCREASING POTENTIAL FOR UNSETTLED
WEATHER FRIDAY NIGHT INTO SATURDAY.

SHORT TERM...TODAY THROUGH SATURDAY
UPPER LOW BEGINS TO LOSE ITS INFLUENCE ON CENTRAL IL TODAY AS IT
FILLS AND LIFTS EAST. MEAN LAYER RH PROGS OFF NAM/GFS SHOW DEEPER
MOISTURE PUSHING EAST THROUGH THE DAY ALLOWING MORE BREAKS FOR
SUN...THOUGH STEEP LLVL LAPSE RATES AND CYCLONIC FLOW WILL PROMOTE
CU/SC DEVELOPMENT FOR MOSTLY CLOUDY SKIES. TRENDED TOWARDS LOWER
GUIDANCE HIGHS OF MID 70S NE TO AROUND 80 IN THE FAR SW. TONIGHT
WITH CLEARING SKIES AND LIGHT WINDS...SEASONABLY COOL LOWS AROUND 60
ARE EXPECTED. UPPER LEVEL HEIGHTS RISE ON FRIDAY AND MORE ABUNDANT
SUNSHINE SHOULD HELP BOOST TEMPS BACK TO NEAR NORMAL...IN THE
LOW/MID 80S.

CLOUDS WILL BE ON THE INCREASE LATE FRIDAY AS A CONVECTIVE COMPLEX
FROM THE PLAINS TRACKS EAST. MID-LEVEL WAVE WILL ACT ON BAROCLINIC
ZONE TO OUR SOUTHWEST AND RETURN FLOW OF MOISTURE UP FROM THE GULF.
LATEST RUN OF NAM/GFS IN BETTER AGREEMENT BRINGING SOME INGREDIENTS
TOGETHER FOR MODERATE RAINS OF 1+ INCHES FRIDAY NIGHT INTO EARLY
SATURDAY FOR THE SOUTHERN THIRD TO HALF OF THE CWA. LLVL THETA-E
ADVECTION AND MOISTURE CONVERGENCE RAMP UP FRIDAY NIGHT...WHILE GOOD
CONVERGENCE SETS UP ALONG 850 MB FRONT WHICH TRACKS NORTH TOWARDS
CENTRAL IL. UPPER LEVEL JET STREAK DIVING THROUGH THE GRT LAKES ALSO
AIDS IN LARGE-SCALE UPPER DIVERGENCE. HAVE BUMPED POPS TO LIKELY
ACROSS THE SOUTH AND TRIED TO FOCUS WITHIN THE 06-18Z SAT TIMEFRAME.
NEWLY ARRIVED ECMWF SHIFTS MAIN PRECIP AXIS FARTHER NORTH AND
LINGERS THROUGH SATURDAY...BUT THIS SEEMS TOO FAR NORTH GIVEN THE
PLACEMENT OF LLVL MOISTURE AND FORCING. SOME ELEVATED INSTABILITY
WARRANTS KEEPING THUNDER MENTION IN...THOUGH THIS MAY BE MARGINAL
NORTH OF I-74. STILL SOME UNCERTAINTY WITH TIMING OF SYSTEM...BUT
DID LOWER SAT AFTERNOON POPS TO LOW CHC BASED ON GFS/NAM BLEND.

LONG TERM...SUNDAY THROUGH WEDNESDAY
WITH FRONT WELL SOUTH OF THE AREA AND NORTHWEST FLOW ACROSS THE
UPPER MIDWEST...EXPECT A PERIOD OF GENERALLY DRY AND SEASONABLE
CONDITIONS. LARGE UPPER RIDGE FROM THE SOUTHWEST APPROACHES BY
MID-WEEK...SO A RETURN TO MORE SUMMERTIME HEAT/HUMIDITY MAY BE ON
TAP FOR THE MIDDLE AND END OF THE WEEK.

25

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KILX 021115
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
615 AM CDT THU JUL 2 2009

.DISCUSSION...
ISSUED 255 AM CDT THU JUL 2 2009

LITTLE CHANGE IN SFC OR UPPER AIR PATTERN FROM LAST COUPLE MORNINGS.
DEEP CUTOFF LOW CONTINUES TO SPIN OVER THE ERN GRT LAKES AND SLOWLY
FILL...00Z ANALYSIS HAD LARGE AREA OF +30M HEIGHT RISES NEAR AND
SOUTH OF THE LOW. LEAD SHORTWAVE TOPPING UPPER RIDGE OVER THE
ROCKIES AND SPARKING A CONVECTIVE COMPLEX IN THE CENTRAL PLAINS.
CYCLONIC FLOW AND STRATUS DECK STILL AFFECTING MOST OF THE CWA...BUT
SOME BREAKS SHOWING UP ACROSS NRN IL...WITH TEMPS IN THESE LOCATIONS
QUICKLY DROPPING OFF INTO THE MID 50S. OTHERWISE INSULATING EFFECT
OF CLOUDS KEEPING MOST AREAS IN LOW/MID 60S DESPITE VERY COOL EARLY
JULY AIRMASS OVERHEAD. MAIN FORECAST ISSUES ARE CLOUD TRENDS AND
IMPACT ON TEMPS TODAY...AND INCREASING POTENTIAL FOR UNSETTLED
WEATHER FRIDAY NIGHT INTO SATURDAY.

SHORT TERM...TODAY THROUGH SATURDAY
UPPER LOW BEGINS TO LOSE ITS INFLUENCE ON CENTRAL IL TODAY AS IT
FILLS AND LIFTS EAST. MEAN LAYER RH PROGS OFF NAM/GFS SHOW DEEPER
MOISTURE PUSHING EAST THROUGH THE DAY ALLOWING MORE BREAKS FOR
SUN...THOUGH STEEP LLVL LAPSE RATES AND CYCLONIC FLOW WILL PROMOTE
CU/SC DEVELOPMENT FOR MOSTLY CLOUDY SKIES. TRENDED TOWARDS LOWER
GUIDANCE HIGHS OF MID 70S NE TO AROUND 80 IN THE FAR SW. TONIGHT
WITH CLEARING SKIES AND LIGHT WINDS...SEASONABLY COOL LOWS AROUND 60
ARE EXPECTED. UPPER LEVEL HEIGHTS RISE ON FRIDAY AND MORE ABUNDANT
SUNSHINE SHOULD HELP BOOST TEMPS BACK TO NEAR NORMAL...IN THE
LOW/MID 80S.

CLOUDS WILL BE ON THE INCREASE LATE FRIDAY AS A CONVECTIVE COMPLEX
FROM THE PLAINS TRACKS EAST. MID-LEVEL WAVE WILL ACT ON BAROCLINIC
ZONE TO OUR SOUTHWEST AND RETURN FLOW OF MOISTURE UP FROM THE GULF.
LATEST RUN OF NAM/GFS IN BETTER AGREEMENT BRINGING SOME INGREDIENTS
TOGETHER FOR MODERATE RAINS OF 1+ INCHES FRIDAY NIGHT INTO EARLY
SATURDAY FOR THE SOUTHERN THIRD TO HALF OF THE CWA. LLVL THETA-E
ADVECTION AND MOISTURE CONVERGENCE RAMP UP FRIDAY NIGHT...WHILE GOOD
CONVERGENCE SETS UP ALONG 850 MB FRONT WHICH TRACKS NORTH TOWARDS
CENTRAL IL. UPPER LEVEL JET STREAK DIVING THROUGH THE GRT LAKES ALSO
AIDS IN LARGE-SCALE UPPER DIVERGENCE. HAVE BUMPED POPS TO LIKELY
ACROSS THE SOUTH AND TRIED TO FOCUS WITHIN THE 06-18Z SAT TIMEFRAME.
NEWLY ARRIVED ECMWF SHIFTS MAIN PRECIP AXIS FARTHER NORTH AND
LINGERS THROUGH SATURDAY...BUT THIS SEEMS TOO FAR NORTH GIVEN THE
PLACEMENT OF LLVL MOISTURE AND FORCING. SOME ELEVATED INSTABILITY
WARRANTS KEEPING THUNDER MENTION IN...THOUGH THIS MAY BE MARGINAL
NORTH OF I-74. STILL SOME UNCERTAINTY WITH TIMING OF SYSTEM...BUT
DID LOWER SAT AFTERNOON POPS TO LOW CHC BASED ON GFS/NAM BLEND.

LONG TERM...SUNDAY THROUGH WEDNESDAY
WITH FRONT WELL SOUTH OF THE AREA AND NORTHWEST FLOW ACROSS THE
UPPER MIDWEST...EXPECT A PERIOD OF GENERALLY DRY AND SEASONABLE
CONDITIONS. LARGE UPPER RIDGE FROM THE SOUTHWEST APPROACHES BY
MID-WEEK...SO A RETURN TO MORE SUMMERTIME HEAT/HUMIDITY MAY BE ON
TAP FOR THE MIDDLE AND END OF THE WEEK.

25
&&

.AVIATION...
ISSUED 615 AM CDT THU JUL 2 2009

MORE HOLES ARE SHOWING UP IN THE STRATOCU FIELD THIS MORN THAN PREV
MORNS...HWVR WITH THE DEEP LYR CYCLONIC FLOW CONTG...EXPECT ANY GAPS
TO BE FILLED BACK IN BY MID MORN. A FEW CLDS IN THE 2500-3000 FT
RANGE HAVE BEEN DRIFTING AROUND...BUT OVERALL CIGS TDY SHOULD BE
VFR IN THE 3K-4K FT RANGE. SOME ISOLD VRY LGT RAIN SHOWING UP ON
RADAR EARLY THIS MORN NE OF A GBG-AAA-MTO LN WITH LTL AFFECT ON
CIGS/VSBYS. MAY INCL SOME -RA BEF 15Z TDY DEPENDING ON LAST MIN
RADAR TRENDS. AS THE ERN GREAT LAKES UPR LOW FINALLY EXITS THE
REGION LATER TDY...LOW LVL FLOW SHOULD BACK TO WLY AND ALLOW AN
EROSION OF THE LOW CLDS W TO E IN THE 00Z-03Z FRI TIME FRAME.

04
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 021101
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
610 AM CDT THU JUL 2 2009

.DISCUSSION...

247 AM...TEMPS BEGIN TO MODERATE TODAY WARMING INTO THE LOWER 80S
FRIDAY...WITH A CHANCE OF THUNDERSTORMS FRIDAY NIGHT INTO SATURDAY.

UPPER LOW OVER THE EASTERN LAKES FINALLY BEGINS TO MOVE EAST
TONIGHT INTO FRIDAY. ONE MORE WEAK WAVE ROTATES SOUTH ACROSS
WESTERN MI TODAY WHICH COULD PRODUCE A SHOWER OVER THE LAKE INTO
NORTHERN INDIANA BUT EXPECT MUCH OF THE CWA TO REMAIN DRY. QUITE A
FEW BREAKS IN THE CLOUDS HAVE DEVELOPED OVERNIGHT. EXPECT THESE TO
FILL IN DURING THE MORNING HRS BUT BY MID/LATE AFTERNOON CLOUDS
SHOULD BEGIN TO SCATTER WITH SUNSHINE ALLOWING TEMPS TO REACH THE
MID 70S BY LATE AFTERNOON.

SKIES MOSTLY CLEAR TONIGHT BUT WITH WAA IN PROGRESS EXPECT TEMPS
TO DROP QUICKLY IN THE EVENING THEN HOLD STEADY THRU THE NIGHT.
FRIDAY SHOULD START MAINLY SUNNY WITH INCREASING HIGH CLOUDS
LATER IN THE DAY. GUIDANCE STILL PUSHING HIGHS INTO THE LOWER 80S
WHICH SEEMS REASONABLE...BUT A LAKE BREEZE MAY KEEP THE LAKESHORE
AREAS A FEW DEGREES COOLER.

FRIDAY NIGHT INTO SATURDAY IS BECOMING MORE UNCERTAIN WITH EACH
NEW MODEL RUN. IT APPEARED 24 HRS AGO THAT A COMPLEX OF TS WOULD
MOVE FROM THE PLAINS TO THE OH VALLEY...WELL SOUTH OF NORTHERN IL
PERHAPS JUST CLIPPING THE SOUTHERN CWA. MODELS CONTINUE TO TRACK
THIS SYSTEM A LITTLE FURTHER NORTH. THE 00Z CANADIAN THIS MORNING
APPEARED TO BE AN OUTLIER AS IT TRACKED THIS SYSTEM RIGHT ACROSS
NORTHERN IL FRIDAY NIGHT...BUT THE NEW 00Z ECMWF IS FURTHER NORTH
WHILE THE LATEST SREF...03Z...SUPPORTS A FURTHER SOUTH TRACK.
THICKNESS PATTERNS WOULD ALL SUGGEST A SOUTHEAST MOVEMENT...OR A
TURN TO THE SOUTHEAST...BUT THAT TURN CONTINUES TO OCCUR FURTHER
NORTH. HAVE MOVED LOW CHANCE POPS FURTHER NORTH FRIDAY NIGHT...
GENERALLY ALONG A ROCHELLE TO RENSSELAER LINE. CONFIDENCE IS NOT
TOO HIGH GIVEN THE CONTINUAL SHIFTING IN THE MODELS BUT WITH THE
UPPER LOW OVER THE LAKES DEPARTING...THE UPPER RIDGE OVER THE
PLAINS MAY BE ABLE TOO BUILD FARTHER NORTHEAST...THUS SHIFTING THE
PRECIP FARTHER NORTHEAST AS WELL. EXPECT CHANGES TO THIS PERIOD OF
THE FORECAST AS LATER RUNS HOPEFULLY PIN DOWN BETTER CONSISTENCY
AND LOCATION. LINGERING PRECIP CHANCES SATURDAY INTO SATURDAY
EVENING DEPENDENT ON HOW FAR NORTH THIS SYSTEM TRACKS. NO CHANGES
AFTER SATURDAY. CMS

&&

.AVIATION...
DISCUSSION REGARDING 12Z TAFS...
610 AM CDT

LARGE AND PERSISTENT UPR LVL LOW NR LK HURON IS FCST TO SLOWLY SHIFT
EWD TODAY.  SATLT TRENDS SHOW LOW RANGE VFR STRATO CU DECK ERODING A
BIT ALONG WRN EDGE OF CIRCULATION.  LARGE HOLE IN OVC HAS DVLPD OVR
SRN WI-NRN IL.  EXPECT THIS IS TEMPORARY AND WILL MAINTAIN A BKN VFR
CIG IN FCST THRU MID MORNING.  ALSO...ENUF COLD AIR ALOFT STILL OVR
RGN TO DVLP INSTABILITY CU LATE MRNG-ERLY AFTN...ESPECIALLY IN AREAS
WHERE SUNSHINE DOES PERSIST INTO THE MID MORNING HRS.

BY THIS EVENING HOWEVER...EXPECT CLOUD BASES TO LIFT AND SCT OUT
AS SFC COOLS.  EXTENSION OF WEAK HI PRESSURE RIDGE TO SHIFT EWD TO
MID/UPR MS VLY BY 00Z AND GRADIENT WILL BE VERY WEAK. AS A
RESULT...NWLY-NNWLY SFC FLOW TO DIMINISH TO BLO 10 KTS BY 00Z...THEN
DROP OFF TO VRBL UNDER 5 KTS BY LATE EVENING AS SKIES CLR AND
CONDITIONS REMAIN VFR THROUGH THURSDAY NIGHT.

MERZLOCK

&&

.MARINE...
245 AM CDT

A LARGE AREA OF LOW PRESSURE NEAR GEORGIAN BAY WILL SLOWLY DRIFT
EASTWARD TO WESTERN QUEBEC TODAY AND TONIGHT. A WEAK HIGH PRESSURE
RIDGE WILL THEN BUILD ACROSS THE WESTERN GREAT LAKES TONIGHT AND
FRIDAY AND REMAIN IN PLACE ACROSS THE UPPER GREAT LAKES THROUGH THE
UPCOMING WEEKEND.

THIS WEAK RIDGE WILL BRING LIGHT WINDS TO LAKE MICHIGAN
THURSDAY NIGHT THROUGH MUCH OF THE UPCOMING WEEKEND.

MERZLOCK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KILX 020755
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
255 AM CDT THU JUL 2 2009

.DISCUSSION...
ISSUED 255 AM CDT THU JUL 2 2009

LITTLE CHANGE IN SFC OR UPPER AIR PATTERN FROM LAST COUPLE
MORNINGS. DEEP CUTOFF LOW CONTINUES TO SPIN OVER THE ERN GRT LAKES
AND SLOWLY FILL...00Z ANALYSIS HAD LARGE AREA OF +30M HEIGHT RISES
NEAR AND SOUTH OF THE LOW. LEAD SHORTWAVE TOPPING UPPER RIDGE OVER
THE ROCKIES AND SPARKING A CONVECTIVE COMPLEX IN THE CENTRAL
PLAINS. CYCLONIC FLOW AND STRATUS DECK STILL AFFECTING MOST OF
THE CWA...BUT SOME BREAKS SHOWING UP ACROSS NRN IL...WITH TEMPS IN
THESE LOCATIONS QUICKLY DROPPING OFF INTO THE MID 50S. OTHERWISE
INSULATING EFFECT OF CLOUDS KEEPING MOST AREAS IN LOW/MID 60S
DESPITE VERY COOL EARLY JULY AIRMASS OVERHEAD. MAIN FORECAST
ISSUES ARE CLOUD TRENDS AND IMPACT ON TEMPS TODAY...AND INCREASING
POTENTIAL FOR UNSETTLED WEATHER FRIDAY NIGHT INTO SATURDAY.

SHORT TERM...TODAY THROUGH SATURDAY
UPPER LOW BEGINS TO LOSE ITS INFLUENCE ON CENTRAL IL TODAY AS IT
FILLS AND LIFTS EAST. MEAN LAYER RH PROGS OFF NAM/GFS SHOW DEEPER
MOISTURE PUSHING EAST THROUGH THE DAY ALLOWING MORE BREAKS FOR
SUN...THOUGH STEEP LLVL LAPSE RATES AND CYCLONIC FLOW WILL PROMOTE
CU/SC DEVELOPMENT FOR MOSTLY CLOUDY SKIES. TRENDED TOWARDS LOWER
GUIDANCE HIGHS OF MID 70S NE TO AROUND 80 IN THE FAR SW. TONIGHT
WITH CLEARING SKIES AND LIGHT WINDS...SEASONABLY COOL LOWS AROUND 60
ARE EXPECTED. UPPER LEVEL HEIGHTS RISE ON FRIDAY AND MORE ABUNDANT
SUNSHINE SHOULD HELP BOOST TEMPS BACK TO NEAR NORMAL...IN THE
LOW/MID 80S.

CLOUDS WILL BE ON THE INCREASE LATE FRIDAY AS A CONVECTIVE COMPLEX
FROM THE PLAINS TRACKS EAST. MID-LEVEL WAVE WILL ACT ON BAROCLINIC
ZONE TO OUR SOUTHWEST AND RETURN FLOW OF MOISTURE UP FROM THE
GULF. LATEST RUN OF NAM/GFS IN BETTER AGREEMENT BRINGING SOME
INGREDIENTS TOGETHER FOR MODERATE RAINS OF 1+ INCHES FRIDAY NIGHT
INTO EARLY SATURDAY FOR THE SOUTHERN THIRD TO HALF OF THE CWA.
LLVL THETA-E ADVECTION AND MOISTURE CONVERGENCE RAMP UP FRIDAY
NIGHT...WHILE GOOD CONVERGENCE SETS UP ALONG 850 MB FRONT WHICH
TRACKS NORTH TOWARDS CENTRAL IL. UPPER LEVEL JET STREAK DIVING
THROUGH THE GRT LAKES ALSO AIDS IN LARGE-SCALE UPPER DIVERGENCE.
HAVE BUMPED POPS TO LIKELY ACROSS THE SOUTH AND TRIED TO FOCUS
WITHIN THE 06-18Z SAT TIMEFRAME. NEWLY ARRIVED ECMWF SHIFTS MAIN
PRECIP AXIS FARTHER NORTH AND LINGERS THROUGH SATURDAY...BUT THIS
SEEMS TOO FAR NORTH GIVEN THE PLACEMENT OF LLVL MOISTURE AND
FORCING. SOME ELEVATED INSTABILITY WARRANTS KEEPING THUNDER
MENTION IN...THOUGH THIS MAY BE MARGINAL NORTH OF I-74. STILL SOME
UNCERTAINTY WITH TIMING OF SYSTEM...BUT DID LOWER SAT AFTERNOON
POPS TO LOW CHC BASED ON GFS/NAM BLEND.

LONG TERM...SUNDAY THROUGH WEDNESDAY
WITH FRONT WELL SOUTH OF THE AREA AND NORTHWEST FLOW ACROSS THE
UPPER MIDWEST...EXPECT A PERIOD OF GENERALLY DRY AND SEASONABLE
CONDITIONS. LARGE UPPER RIDGE FROM THE SOUTHWEST APPROACHES BY
MID-WEEK...SO A RETURN TO MORE SUMMERTIME HEAT/HUMIDITY MAY BE ON
TAP FOR THE MIDDLE AND END OF THE WEEK.

25

&&

.AVIATION...
ISSUED 1151 PM CDT WED JUL 1 2009

CLOUD COVER REMAINS OVER ALL SITES DUE TO CONTINUE CYCLONIC FLOW
WITH UPPER LEVEL LOW STILL IN THE GRT LKS REGION. SOME BREAKS SEEN
ON SATELLITE LOOP BUT DIFFICULT TO TIME INTO THE SITES AND NOT
CONFIDENT THAT THE BREAKS WILL GET TO ANY OF THE SITES. SO WILL
KEEP CIGS AT ALL SITES AT VFR LEVELS. LITTLE SHOWER SEEN ON RADAR
LOOP BUT BELIEVE THIS WILL NOT AFFECT ANY TAF SITES AFTER 06Z.
CLOUD COVER CONTINUES INTO TOMORROW AT ALL SITES BUT WILL BEGIN TO
SCATTER OUT IN THE EVENING AS THE UPPER LVL LOW PULLS NORTHEAST
AWAY FROM THE AREA. WINDS WILL REMAIN LIGHT OVERNIGHT AND THEN
INCREASE TOMORROW MORNING OUT OF THE NORTHWEST...THEN LIGHT WINDS
AGAIN TOMORROW EVENING.

AUTEN
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 020747
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
247 AM CDT THU JUL 2 2009

.DISCUSSION...

247 AM...TEMPS BEGIN TO MODERATE TODAY WARMING INTO THE LOWER 80S
FRIDAY...WITH A CHANCE OF THUNDERSTORMS FRIDAY NIGHT INTO SATURDAY.

UPPER LOW OVER THE EASTERN LAKES FINALLY BEGINS TO MOVE EAST
TONIGHT INTO FRIDAY. ONE MORE WEAK WAVE ROTATES SOUTH ACROSS
WESTERN MI TODAY WHICH COULD PRODUCE A SHOWER OVER THE LAKE INTO
NORTHERN INDIANA BUT EXPECT MUCH OF THE CWA TO REMAIN DRY. QUITE A
FEW BREAKS IN THE CLOUDS HAVE DEVELOPED OVERNIGHT. EXPECT THESE TO
FILL IN DURING THE MORNING HRS BUT BY MID/LATE AFTERNOON CLOUDS
SHOULD BEGIN TO SCATTER WITH SUNSHINE ALLOWING TEMPS TO REACH THE
MID 70S BY LATE AFTERNOON.

SKIES MOSTLY CLEAR TONIGHT BUT WITH WAA IN PROGRESS EXPECT TEMPS
TO DROP QUICKLY IN THE EVENING THEN HOLD STEADY THRU THE NIGHT.
FRIDAY SHOULD START MAINLY SUNNY WITH INCREASING HIGH CLOUDS
LATER IN THE DAY. GUIDANCE STILL PUSHING HIGHS INTO THE LOWER 80S
WHICH SEEMS REASONABLE...BUT A LAKE BREEZE MAY KEEP THE LAKESHORE
AREAS A FEW DEGREES COOLER.

FRIDAY NIGHT INTO SATURDAY IS BECOMING MORE UNCERTAIN WITH EACH
NEW MODEL RUN. IT APPEARED 24 HRS AGO THAT A COMPLEX OF TS WOULD
MOVE FROM THE PLAINS TO THE OH VALLEY...WELL SOUTH OF NORTHERN IL
PERHAPS JUST CLIPPING THE SOUTHERN CWA. MODELS CONTINUE TO TRACK
THIS SYSTEM A LITTLE FURTHER NORTH. THE 00Z CANADIAN THIS MORNING
APPEARED TO BE AN OUTLIER AS IT TRACKED THIS SYSTEM RIGHT ACROSS
NORTHERN IL FRIDAY NIGHT...BUT THE NEW 00Z ECMWF IS FURTHER NORTH
WHILE THE LATEST SREF...03Z...SUPPORTS A FURTHER SOUTH TRACK.
THICKNESS PATTERNS WOULD ALL SUGGEST A SOUTHEAST MOVEMENT...OR A
TURN TO THE SOUTHEAST...BUT THAT TURN CONTINUES TO OCCUR FURTHER
NORTH. HAVE MOVED LOW CHANCE POPS FURTHER NORTH FRIDAY NIGHT...
GENERALLY ALONG A ROCHELLE TO RENSSELAER LINE. CONFIDENCE IS NOT
TOO HIGH GIVEN THE CONTINUAL SHIFTING IN THE MODELS BUT WITH THE
UPPER LOW OVER THE LAKES DEPARTING...THE UPPER RIDGE OVER THE
PLAINS MAY BE ABLE TOO BUILD FARTHER NORTHEAST...THUS SHIFTING THE
PRECIP FARTHER NORTHEAST AS WELL. EXPECT CHANGES TO THIS PERIOD OF
THE FORECAST AS LATER RUNS HOPEFULLY PIN DOWN BETTER CONSISTENCY
AND LOCATION. LINGERING PRECIP CHANCES SATURDAY INTO SATURDAY
EVENING DEPENDENT ON HOW FAR NORTH THIS SYSTEM TRACKS. NO CHANGES
AFTER SATURDAY. CMS

&&

.AVIATION...
DISCUSSION REGARDING 06Z TAFS...
1245 AM CDT

LARGE AND PERSISTENT UPR LVL LOW NR LK HURON IS FCST TO SLOWLY SHIFT
EWD TODAY.  SATLT TRENDS SHOW LOW RANGE VFR STRATO CU DECK ERODING A
BIT ALONG WRN EDGE OF CIRCULATION.  LARGE HOLE IN OVC HAS DVLPD OVR
SRN WI-NRN IL.  EXPECT THIS IS TEMPORARY AND WILL MAINTAIN A BKN VFR
CIG IN FCST THRU MID MORNING.  ALSO...ENUF COLD AIR ALOFT STILL OVR
RGN TO DVLP INSTABILITY CU LATE MRNG-ERLY AFTN WHERE SUNSHINE DOES
PERSIST INTO THE MORNING HRS.

BY THIS EVENING HOWEVER...EXPECT CLOUD BASES TO LIFT AND SCT OUT
AS SFC COOLS.  EXTENSION OF WEAK HI PRESSURE RIDGE TO SHIFT EWD TO
MID/UPR MS VLY BY 00Z AND GRADIENT WILL BE VERY WEAK. AS A
RESULT...NWLY-NNWLY SFC FLOW TO DIMINISH TO BLO 10 KTS BY 00Z...THEN
DROP OFF TO VRBL UNDER 5 KTS BY LATE EVENING AS SKIES CLR AND
CONDITIONS REMAIN VFR THROUGH THURSDAY NIGHT.

MERZLOCK

&&

.MARINE...
245 AM CDT

A LARGE AREA OF LOW PRESSURE NEAR GEORGIAN BAY WILL SLOWLY DRIFT
EASTWARD TO WESTERN QUEBEC TODAY AND TONIGHT. A WEAK HIGH PRESSURE
RIDGE WILL THEN BUILD ACROSS THE WESTERN GREAT LAKES TONIGHT AND
FRIDAY AND REMAIN IN PLACE ACROSS THE UPPER GREAT LAKES THROUGH THE
UPCOMING WEEKEND.

THIS WEAK RIDGE WILL BRING LIGHT WINDS TO LAKE MICHIGAN
THURSDAY NIGHT THROUGH MUCH OF THE UPCOMING WEEKEND.

MERZLOCK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KLOT 020739
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
245 AM CDT THU JUL 2 2009

.DISCUSSION...
310 PM CDT

ONE WOULD CERTAINLY NOT GUESS JULY 1ST IF SHOWN THE CURRENT WATER
VAPOR SATELLITE LOOP OR A 500 HPA HEIGHT ANALYSIS. A QUICK BUT
TEMPORARY SWITCH TO DOGS DAYS OF SUMMER TYPE WX LAST WEEK BUT
LAST FEW DAYS THE WE HAVE GONE RIGHT BACK TO TYPICAL FOR THIS YEAR
ATYPICALLY AMPLIFIED AND ACTIVE UPPER PATTERN DROPPING US WELL
BACK BELOW NORMAL TEMPERATURE WISE. SOLID CLOUD COVER AND A BIT OF
A BREEZE OUT OF THE NW JUST ADDING TO COOL FALLISH FEEL.

SLOW DE-AMPLIFICATION OF PATTERN OVER WESTERN AND CENTRAL NOAM
BEGINNING OVERNIGHT AND CARRYING ON INTO THE HOLIDAY WEEKEND WILL
ALLOW TEMPS TO MODERATE TO NEAR IF NOT TO NORMAL DAYTIME MAXIMA IN
LOWER AND MID 80S.

SLUGGISH UPPER PATTERN WITH UPPER ANTICYCLONE PARKED OVER THE
CANADIAN MARITIMES PREVENTING CENTRAL/LOWER GREAT LAKES UPPER LOW
FROM MAKING ANY SIGNIFICANT PROGRESS E OR NE...WHILE RIDGE OVER
THE ROCKIES AND HIGH PLAINS MAINTAINS NNW TO NW FLOW FROM THE UPPER
MIDWEST TO THE OH VALLEY.

MAIN RA AREA REMAINS ASSOCIATED WITH THE MID LEVEL LOW OVER LOWER
MI WHILE MINOR IMPULSES ROTATING AROUND IT OCCASIONALLY SWING
SCATTERED LIGHT SHOWERS AROUND THE REGION. ONE OF THESE CURRENTLY
DROPPING OUT OF SE WI OVER NORTHERN IL THO ONLY TRACE TO A COUPLE
HUNDREDTHS OF RA DETECTED FROM THESE -SHRA. THESE TO PASS BY THE
LOCAL FORECAST AREA DURING THE REST OF THE AFTERNOON.

WITH ONLY SLOW MOVEMENT OF MID-UPPER LOW TO THE NE OVERNIGHT
EXPECT WIDESPREAD CLOUDINESS TO REMAIN AS BACK EDGE STILL ACROSS N
CENTRAL AND SE MN AS WELL AND EASTERN IA. THERE HAD BEEN ANOTHER
AREA OF SCATTERED -SHRA AROUND THE DOOR CO AND BAY OF GREEN BAY
AREA AS ANOTHER IMPULSE DROPPED DOWN THE W SIDE OF THE UPPER
CIRCULATION BUT AT LEAST ACCORDING TO RADAR HAVE PRETTY MUCH
DRIED UP. THE DISTURBANCE THAT WAS GENERATING THESE -SHRA WILL
START TO TURN TO THE SE AND WITH CENTER OF MAIN CIRCULATION
GRADUALLY BEGINNING TO SHIFT A LITTLE TO THE E AND NE WOULD EXPECT
IF ANY -SHRA REDEVELOP TONIGHT THEY WILL PASS OVER SOUTHERN LAKE
MI AND MISS NE IL THO HAVE HELD ON TO A TOKEN SLIGHT CHC POP VALUE
FOR NW IND THRU 06Z TONIGHT.

BY LATER IN THE DAY THU THE CENTER OF THE UPPER LOW SHIFT TO OVER
SOUTHERN ONTARIO AS STRONG SHORT WAVE CURRENTLY BOTTOMING THE
WESTERN CANADA UPPER LOW EJECTS ACROSS THE SOUTHERN CANADIAN
PRAIRIE. THIS INDUCES RIDGING DOWNSTREAM OVER THE UPPER MS VALLEY
AND SKIES SHOULD BE CLEARING WITH TIME FROM W TO E. THIS SHORT
WAVE PROGGED TO FORM ANOTHER CLOSED LOW OVER CENTRAL ONTARIO BY
FRI MORNING AND THEN DROP TO SOUTHERN QUEBEC BY LATE FRI NIGHT.

THIS MAINTAINS A WNW UPPER FLOW ACROSS THE REGION BUT ALLOWS MILDER
AIR ALREADY IN PLACE ACROSS THE PLAINS N INTO S CENTRAL CANADA TO
BEGIN TO SHIFT E OVER THE UPPER AND MID MS VALLEY AND MODERATING
TEMPERATURES.

ON THE MIND OF MOST IS HOW HOLIDAY WEEKEND LOOKS. LONGER RANGE
MODEL OUTPUT SHOW A SLOW MOVING SURFACE WAVE MOVING E OUT OF THE
CENTRAL PLAINS AS THE IMPULSE CURRENTLY SEEN OVER THE PACIFIC AT
130W 27N EVENTUALLY PUSHES THRU THE UPPER RIDGE OVER THE
ROCKIES...AND COMES OUT OVER THE CENTRAL PLAINS ON FRI. IT THEN
SLOWLY MOVES ESE AS IT TRANSITIONS FROM THE UPPER RIDGE INTO THE
UPPER TROF PROGGED OVER EASTERN CANADA AND THE EASTERN US. HAVE
LOW CHANCE POPS FOR THE FAR SW AND SOUTHERN COUNTIES OF THE LOCAL
FA FRI NIGHT AND SAT AS THE SFC LOW PASSES ACROSS CENTRAL IL
TOWARD THE LOWER OH VALLEY. THEREAFTER...REST OF WEEKEND AND
EARLY NEXT WEEK LOOKS DRY WITH SEASONAL TEMPS BUT COOLER NEAR THE
LAKE SAT...SUN...MON WITH SFC HI SETTLING OVER THE GREAT LAKES.

TRS

&&

.AVIATION...
DISCUSSION REGARDING 06Z TAFS...
1245 AM CDT

LARGE AND PERSISTENT UPR LVL LOW NR LK HURON IS FCST TO SLOWLY SHIFT
EWD TODAY.  SATLT TRENDS SHOW LOW RANGE VFR STRATO CU DECK ERODING A
BIT ALONG WRN EDGE OF CIRCULATION.  LARGE HOLE IN OVC HAS DVLPD OVR
SRN WI-NRN IL.  EXPECT THIS IS TEMPORARY AND WILL MAINTAIN A BKN VFR
CIG IN FCST THRU MID MORNING.  ALSO...ENUF COLD AIR ALOFT STILL OVR
RGN TO DVLP INSTABILITY CU LATE MRNG-ERLY AFTN WHERE SUNSHINE DOES
PERSIST INTO THE MORNING HRS.

BY THIS EVENING HOWEVER...EXPECT CLOUD BASES TO LIFT AND SCT OUT
AS SFC COOLS.  EXTENSION OF WEAK HI PRESSURE RIDGE TO SHIFT EWD TO
MID/UPR MS VLY BY 00Z AND GRADIENT WILL BE VERY WEAK. AS A
RESULT...NWLY-NNWLY SFC FLOW TO DIMINISH TO BLO 10 KTS BY 00Z...THEN
DROP OFF TO VRBL UNDER 5 KTS BY LATE EVENING AS SKIES CLR AND
CONDITIONS REMAIN VFR THROUGH THURSDAY NIGHT.

MERZLOCK

&&

.MARINE...
245 AM CDT

A LARGE AREA OF LOW PRESSURE NEAR GEORGIAN BAY WILL SLOWLY DRIFT
EASTWARD TO WESTERN QUEBEC TODAY AND TONIGHT. A WEAK HIGH PRESSURE
RIDGE WILL THEN BUILD ACROSS THE WESTERN GREAT LAKES TONIGHT AND
FRIDAY AND REMAIN IN PLACE ACROSS THE UPPER GREAT LAKES THROUGH THE
UPCOMING WEEKEND.

THIS WEAK RIDGE WILL BRING LIGHT WINDS TO LAKE MICHIGAN
THURSDAY NIGHT THROUGH MUCH OF THE UPCOMING WEEKEND.

MERZLOCK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KLOT 020545
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1245 AM CDT THU JUL 2 2009

.DISCUSSION...
310 PM CDT

ONE WOULD CERTAINLY NOT GUESS JULY 1ST IF SHOWN THE CURRENT WATER
VAPOR SATELLITE LOOP OR A 500 HPA HEIGHT ANALYSIS. A QUICK BUT
TEMPORARY SWITCH TO DOGS DAYS OF SUMMER TYPE WX LAST WEEK BUT
LAST FEW DAYS THE WE HAVE GONE RIGHT BACK TO TYPICAL FOR THIS YEAR
ATYPICALLY AMPLIFIED AND ACTIVE UPPER PATTERN DROPPING US WELL
BACK BELOW NORMAL TEMPERATURE WISE. SOLID CLOUD COVER AND A BIT OF
A BREEZE OUT OF THE NW JUST ADDING TO COOL FALLISH FEEL.

SLOW DE-AMPLIFICATION OF PATTERN OVER WESTERN AND CENTRAL NOAM
BEGINNING OVERNIGHT AND CARRYING ON INTO THE HOLIDAY WEEKEND WILL
ALLOW TEMPS TO MODERATE TO NEAR IF NOT TO NORMAL DAYTIME MAXIMA IN
LOWER AND MID 80S.

SLUGGISH UPPER PATTERN WITH UPPER ANTICYCLONE PARKED OVER THE
CANADIAN MARITIMES PREVENTING CENTRAL/LOWER GREAT LAKES UPPER LOW
FROM MAKING ANY SIGNIFICANT PROGRESS E OR NE...WHILE RIDGE OVER
THE ROCKIES AND HIGH PLAINS MAINTAINS NNW TO NW FLOW FROM THE UPPER
MIDWEST TO THE OH VALLEY.

MAIN RA AREA REMAINS ASSOCIATED WITH THE MID LEVEL LOW OVER LOWER
MI WHILE MINOR IMPULSES ROTATING AROUND IT OCCASIONALLY SWING
SCATTERED LIGHT SHOWERS AROUND THE REGION. ONE OF THESE CURRENTLY
DROPPING OUT OF SE WI OVER NORTHERN IL THO ONLY TRACE TO A COUPLE
HUNDREDTHS OF RA DETECTED FROM THESE -SHRA. THESE TO PASS BY THE
LOCAL FORECAST AREA DURING THE REST OF THE AFTERNOON.

WITH ONLY SLOW MOVEMENT OF MID-UPPER LOW TO THE NE OVERNIGHT
EXPECT WIDESPREAD CLOUDINESS TO REMAIN AS BACK EDGE STILL ACROSS N
CENTRAL AND SE MN AS WELL AND EASTERN IA. THERE HAD BEEN ANOTHER
AREA OF SCATTERED -SHRA AROUND THE DOOR CO AND BAY OF GREEN BAY
AREA AS ANOTHER IMPULSE DROPPED DOWN THE W SIDE OF THE UPPER
CIRCULATION BUT AT LEAST ACCORDING TO RADAR HAVE PRETTY MUCH
DRIED UP. THE DISTURBANCE THAT WAS GENERATING THESE -SHRA WILL
START TO TURN TO THE SE AND WITH CENTER OF MAIN CIRCULATION
GRADUALLY BEGINNING TO SHIFT A LITTLE TO THE E AND NE WOULD EXPECT
IF ANY -SHRA REDEVELOP TONIGHT THEY WILL PASS OVER SOUTHERN LAKE
MI AND MISS NE IL THO HAVE HELD ON TO A TOKEN SLIGHT CHC POP VALUE
FOR NW IND THRU 06Z TONIGHT.

BY LATER IN THE DAY THU THE CENTER OF THE UPPER LOW SHIFT TO OVER
SOUTHERN ONTARIO AS STRONG SHORT WAVE CURRENTLY BOTTOMING THE
WESTERN CANADA UPPER LOW EJECTS ACROSS THE SOUTHERN CANADIAN
PRAIRIE. THIS INDUCES RIDGING DOWNSTREAM OVER THE UPPER MS VALLEY
AND SKIES SHOULD BE CLEARING WITH TIME FROM W TO E. THIS SHORT
WAVE PROGGED TO FORM ANOTHER CLOSED LOW OVER CENTRAL ONTARIO BY
FRI MORNING AND THEN DROP TO SOUTHERN QUEBEC BY LATE FRI NIGHT.

THIS MAINTAINS A WNW UPPER FLOW ACROSS THE REGION BUT ALLOWS MILDER
AIR ALREADY IN PLACE ACROSS THE PLAINS N INTO S CENTRAL CANADA TO
BEGIN TO SHIFT E OVER THE UPPER AND MID MS VALLEY AND MODERATING
TEMPERATURES.

ON THE MIND OF MOST IS HOW HOLIDAY WEEKEND LOOKS. LONGER RANGE
MODEL OUTPUT SHOW A SLOW MOVING SURFACE WAVE MOVING E OUT OF THE
CENTRAL PLAINS AS THE IMPULSE CURRENTLY SEEN OVER THE PACIFIC AT
130W 27N EVENTUALLY PUSHES THRU THE UPPER RIDGE OVER THE
ROCKIES...AND COMES OUT OVER THE CENTRAL PLAINS ON FRI. IT THEN
SLOWLY MOVES ESE AS IT TRANSITIONS FROM THE UPPER RIDGE INTO THE
UPPER TROF PROGGED OVER EASTERN CANADA AND THE EASTERN US. HAVE
LOW CHANCE POPS FOR THE FAR SW AND SOUTHERN COUNTIES OF THE LOCAL
FA FRI NIGHT AND SAT AS THE SFC LOW PASSES ACROSS CENTRAL IL
TOWARD THE LOWER OH VALLEY. THEREAFTER...REST OF WEEKEND AND
EARLY NEXT WEEK LOOKS DRY WITH SEASONAL TEMPS BUT COOLER NEAR THE
LAKE SAT...SUN...MON WITH SFC HI SETTLING OVER THE GREAT LAKES.

TRS

&&

.AVIATION...
DISCUSSION REGARDING 06Z TAFS...
1245 AM CDT

LARGE AND PERSISTENT UPR LVL LOW NR LK HURON IS FCST TO SLOWLY SHIFT
EWD TODAY.  SATLT TRENDS SHOW LOW RANGE VFR STRATO CU DECK ERODING A
BIT ALONG WRN EDGE OF CIRCULATION.  LARGE HOLE IN OVC HAS DVLPD OVR
SRN WI-NRN IL.  EXPECT THIS IS TEMPORARY AND WILL MAINTAIN A BKN VFR
CIG IN FCST THRU MID MORNING.  ALSO...ENUF COLD AIR ALOFT STILL OVR
RGN TO DVLP INSTABILITY CU LATE MRNG-ERLY AFTN WHERE SUNSHINE DOES
PERSIST INTO THE MORNING HRS.

BY THIS EVENING HOWEVER...EXPECT CLOUD BASES TO LIFT AND SCT OUT
AS SFC COOLS.  EXTENSION OF WEAK HI PRESSURE RIDGE TO SHIFT EWD TO
MID/UPR MS VLY BY 00Z AND GRADIENT WILL BE VERY WEAK. AS A
RESULT...NWLY-NNWLY SFC FLOW TO DIMINISH TO BLO 10 KTS BY 00Z...THEN
DROP OFF TO VRBL UNDER 5 KTS BY LATE EVENING AS SKIES CLR AND
CONDITIONS REMAIN VFR THROUGH THURSDAY NIGHT.

MERZLOCK

&&

.MARINE...
250 PM CDT

DEEP UPPER LEVEL CUT OFF LOW CONTINUES TO SPIN NEAR LAKE HURON
MORE TYPICAL OF OCTOBER THAN JULY. BROAD CYCLONIC FLOW ASSOCIATED
WITH THIS LOW WILL PERSIST AT THE SURFACE THROUGH THURSDAY AS THE LOW
ONLY SLOWLY WEAKENS. AS HEIGHTS BUILD ALOFT... THE SURFACE AND
BOUNDARY LAYER FLOW WILL BECOME MORE NEUTRAL AS WEAK SURFACE
RIDGING BUILDS INTO THE AREA FROM THE WEST. THE UPPER CUT OFF LOW
FINALLY OPENS INTO A WAVE LATE THURSDAY AND THEN DRIFTS EAST
FRIDAY ALLOWING A WEAK SURFACE RIDGE TO MOVE OVERHEAD.

AFOREMENTIONED WEAK RIDGE WILL BRING LIGHT WINDS TO LAKE MICHIGAN
THURSDAY NIGHT THROUGH FRIDAY INTO SATURDAY. ANOTHER UPPER LEVEL
LOW DIVES SOUTHEAST INTO THE EASTERN GREAT LAKES ON SATURDAY
HELPING TO MAINTAIN A WEAK NORTHWEST FLOW ALOFT OVER THE REGION
THROUGH THE REMINDER OF THE HOLIDAY WEEKEND. THIS ALLOWS FOR A
CONTINUED WEAK SURFACE GRADIENT PATTERN YIELDING LIGHT WINDS
THROUGHOUT THE PERIOD OVER THE WATER.

ED F

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KILX 020451
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1151 PM CDT WED JUL 1 2009

.DISCUSSION...
ISSUED 855 PM CDT WED JUL 1 2009

CLOUDY SKIES WILL CONTINUE OVERNIGHT AS CWA REMAINS IN CYCLONIC
FLOW WITH UPPER LEVEL SYSTEM STILL IN THE GRT LKS REGION. CLOUD
COVER LAST NIGHT KEPT TEMPS UP AND BELIEVE THIS IS POSSIBLE AGAIN
TONIGHT. SO WILL RAISE OVERNIGHT LOWS UP SOME TO ACCOUNT FOR THIS.
REMAINDER OF FCST LOOKS FINE AND UPDATE WILL BE COMING OUT SHORTLY.

AUTEN
&&

.AVIATION...
ISSUED 1151 PM CDT WED JUL 1 2009

CLOUD COVER REMAINS OVER ALL SITES DUE TO CONTINUE CYCLONIC FLOW
WITH UPPER LEVEL LOW STILL IN THE GRT LKS REGION. SOME BREAKS SEEN
ON SATELLITE LOOP BUT DIFFICULT TO TIME INTO THE SITES AND NOT
CONFIDENT THAT THE BREAKS WILL GET TO ANY OF THE SITES. SO WILL
KEEP CIGS AT ALL SITES AT VFR LEVELS. LITTLE SHOWER SEEN ON RADAR
LOOP BUT BELIEVE THIS WILL NOT AFFECT ANY TAF SITES AFTER 06Z.
CLOUD COVER CONTINUES INTO TOMORROW AT ALL SITES BUT WILL BEGIN TO
SCATTER OUT IN THE EVENING AS THE UPPER LVL LOW PULLS NORTHEAST
AWAY FROM THE AREA. WINDS WILL REMAIN LIGHT OVERNIGHT AND THEN
INCREASE TOMORROW MORNING OUT OF THE NORTHWEST...THEN LIGHT WINDS
AGAIN TOMORROW EVENING.

AUTEN
&&

.PREV DISCUSSION...
ISSUED 239 PM CDT WED JUL 1 2009

PRIMARY SHORT-TERM CHALLENGE WILL BE TIMING OF CLEARING TREND
LATE TONIGHT INTO TOMORROW. AFTER THAT...EMPHASIS WILL SHIFT TO
RAIN CHANCES OVER THE UPCOMING HOLIDAY WEEKEND.

18Z SURFACE CHART SHOWS NEARLY STATIONARY FRONTAL BOUNDARY ACROSS
THE TENNESSEE RIVER VALLEY...WITH A MUCH COOLER AND DRIER AIRMASS
FIRMLY IN PLACE ACROSS CENTRAL ILLINOIS. ALOFT...UNSEASONABLY STRONG
LOW PRESSURE CONTINUES TO SPIN OVER THE EASTERN GREAT LAKES...WHILE
NUMEROUS SHORT-WAVES ROTATE AROUND THIS FEATURE THROUGH THE
MIDWEST. AS A RESULT...EXTENSIVE CLOUD COVER EXISTS ACROSS MUCH OF
THE REGION...AS FAR WEST AS THE CENTRAL AND EASTERN SECTIONS OF
IOWA AND MISSOURI.

SHORT TERM...TONIGHT THROUGH SATURDAY

MAIN QUESTION IN THE IMMEDIATE SHORT-TERM IS WHETHER SKIES WILL
CLEAR TONIGHT. MODELS HAVE A GOOD HANDLE ON THE CURRENT MID AND
LOW-LEVEL RH FIELDS...HOWEVER THEIR FORECAST DEPICTIONS OF HOW
THESE FIELDS WILL EVOLVE DO NOT PROVIDE MUCH FORECAST
ASSISTANCE...AS BOTH THE NAM-WRF AND GFS INDICATE A GOOD DEAL OF
MID-LEVEL DRYING BUT SHOW PERSISTENT LOW-LEVEL MOISTURE THROUGH
THE NIGHT. THE CORRESPONDING NUMERIC GUIDANCE SHOWS CONFLICTING
INFORMATION...WITH THE MET KEEPING CONDITIONS CLOUDY AND THE MAV
CLEARING THINGS OUT. STRONG UPPER LOW HAS SHOWN NO INDICATION OF
AN EASTWARD MOVE TODAY AND NEITHER MODEL SUGGESTS MUCH
MOVEMENT/WEAKENING UNTIL THURSDAY MORNING AT THE EARLIEST. WITH
THE LOW REMAINING ESSENTIALLY STATIONARY AND A CONTINUED NORTHERLY
FETCH OVERNIGHT...AM NOT OPTIMISTIC ABOUT CLEARING ANYTIME SOON.
HAVE THEREFORE MAINTAINED A CLOUDY FORECAST THROUGH TONIGHT.

UPPER LOW SLOWLY LIFTS E/NE ON THURSDAY...RESULTING IN
INCREASINGLY ANTICYCLONIC FLOW. AS UPPER/SURFACE HIGH PRESSURE
BUILD IN FROM THE WEST...THINK SKIES WILL PARTIALLY CLEAR FROM
WEST TO EAST THURSDAY MORNING...HOWEVER WITH COLD AIR ALOFT AND
CU-RULE SHOWING STRONGLY NEGATIVE VALUES OVER THE AREA...THINK ANY
MORNING SUNSHINE WILL BE REPLACED BY PLENTY OF DIURNAL AFTERNOON
CLOUDS. DESPITE A GOOD DEAL OF CLOUD COVER...LIGHT WESTERLY WINDS
AND AT LEAST PARTIAL JULY SUNSHINE WILL BOOST HIGH TEMPS SEVERAL
DEGREES HIGHER THAN TODAY. NUMERIC GUIDANCE EXHIBITS A LARGE
SPREAD IN VALUES...WITH SOME SITES SHOWING A 6 TO 12 DEGREE
DIFFERENCE. BASED ON EXPECTED AMOUNT OF SUNSHINE...WILL LEAN
TOWARD THE WARMER MAV NUMBERS...RESULTING IN HIGHS RANGING FROM
THE MIDDLE 70S ACROSS THE WABASH RIVER VALLEY TO AROUND 80 DEGREES
WEST OF THE ILLINOIS RIVER. SKIES WILL RAPIDLY CLEAR OUT AFTER
SUNSET THURSDAY EVENING...AND WITH LIGHT WINDS EXPECTED HAVE
UNDERCUT GUIDANCE BY A FEW DEGREES FOR LOW TEMPS. SHOULD BE
ANOTHER CHILLY NIGHT...WITH LOWS BOTTOMING OUT IN THE UPPER 50S IN
MOST LOCATIONS.

AS UPPER LOW MOVES FURTHER AWAY...RIDGING WILL TEMPORARILY TAKE
HOLD ACROSS THE MIDWEST ON FRIDAY. WITH MOSTLY SUNNY SKIES
EXPECTED...HIGHS WILL QUICKLY REBOUND INTO THE LOWER TO MIDDLE
80S. STRONG SHORT-WAVE IS PROGGED TO RIDE UP AND OVER THE CREST
OF THE RIDGE LATE FRIDAY...RESULTING IN MCS DEVELOPMENT OVER PARTS
OF THE PLAINS STATES FRIDAY EVENING. CONVECTIVE COMPLEX WILL THEN
TRACK E/SE ALONG AND NORTH OF STATIONARY FRONTAL BOUNDARY
STRETCHING FROM CENTRAL MISSOURI INTO KENTUCKY. MODELS STILL IN
DISAGREEMENT WITH THE EXACT TRACK OF THE MCS...WITH THE 12Z ECMWF
CONTINUING TO BE FURTHER NORTH THAN THE GFS/NAM-WRF. LATEST RUN OF THE
GFS HAS SHIFTED THE RAIN BAND SLIGHTLY FURTHER NORTH THAN ITS
PREVIOUS RUNS...BUT NOT AS FAR NORTH AS THE ECMWF. NAM-WRF
SUPPORTS THE GFS...WHILE CANADIAN RESEMBLES THE ECMWF. GIVEN
UNFAVORABLE UPPER FLOW TO BRING FOCUSING FRONTAL BOUNDARY FURTHER
NORTH...WILL FOLLOW THE MORE SOUTHERN GFS/NAM-WRF SOLUTION.
RESULTING HEAVIEST RAIN AXIS WILL SET UP FROM NORTHERN MISSOURI
E/SE INTO SOUTH-CENTRAL ILLINOIS LATE FRIDAY NIGHT INTO SATURDAY
MORNING. HAVE THEREFORE INCREASED POPS SUBSTANTIALLY FRIDAY
NIGHT...RANGING FROM 30S ALONG AND NORTH OF I-74 TO 50S ACROSS THE
S/SW ZONES.

ONCE MCS ROLLS THROUGH SATURDAY MORNING...BEST PRECIP CHANCES WILL
LIKELY SHIFT FURTHER SOUTH SATURDAY AFTERNOON/EVENING...AS PRIMARY
OUTFLOW GETS SHUNTED INTO MISSOURI/WESTERN KENTUCKY. HOWEVER...WITH
SYNOPTIC FRONT NEARBY AND SMALLER OUTFLOW BOUNDARIES LEFT
BEHIND FROM MORNING CONVECTION...THINK CHANCE POPS STILL HAVE TO
BE MENTIONED FOR THE EVENING OF JULY 4. WILL ONLY CARRY 20 POPS
ACROSS MUCH OF THE AREA...WITH 30S ACROSS THE SOUTH.

LONG TERM...SUNDAY THROUGH WEDNESDAY

THE EXTENDED FORECAST WILL FEATURE NEAR NORMAL TEMPS AND BELOW
NORMAL PRECIP...AS ZONAL FLOW DOMINATES MUCH OF THE CONUS. 12Z
ECMWF SUGGESTS ANOTHER DEEP UPPER LOW DEVELOPING OVER THE EASTERN
GREAT LAKES EARLY IN THE PERIOD THEN MIGRATING S/SW INTO THE DEEP
SOUTH BY THE END OF THE WEEK...BUT THIS SOLUTION HAS BEEN
REJECTED. WILL STICK WITH THE GFS...WHICH INDICATES SLOWLY WARMING
TEMPS SUNDAY THROUGH WEDNESDAY. A WEAK DISTURBANCE MAY BRING A FEW
SHOWERS INTO THE AREA ON MONDAY...BUT HAVE LEFT OUT OF THE
FORECAST FOR NOW PENDING SUPPORT FROM ADDITIONAL MODEL RUNS.

BARNES


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KILX 020155
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
855 PM CDT WED JUL 1 2009

.DISCUSSION...
ISSUED 855 PM CDT WED JUL 1 2009

CLOUDY SKIES WILL CONTINUE OVERNIGHT AS CWA REMAINS IN CYCLONIC
FLOW WITH UPPER LEVEL SYSTEM STILL IN THE GRT LKS REGION. CLOUD
COVER LAST NIGHT KEPT TEMPS UP AND BELIEVE THIS IS POSSIBLE AGAIN
TONIGHT. SO WILL RAISE OVERNIGHT LOWS UP SOME TO ACCOUNT FOR THIS.
REMAINDER OF FCST LOOKS FINE AND UPDATE WILL BE COMING OUT SHORTLY.

AUTEN
&&

.AVIATION...
ISSUED 557 PM CDT WED JUL 1 2009

CYCLONIC FLOW CONTINUES OVER THE AREA AND WILL KEEP CLOUDS OVER
ALL TAF SITES REMAINDER OF THE NIGHT AND INTO TOMORROW MORNING.
SPI SHOULD BEGIN TO CLEAR FIRST AS THE UPPER LVL LOW LIFTS
NORTHEAST TOMORROW...FOLLOWED BY DEC...AND THEN PIA...BMI AND CMI.
SCATTERING OUT SHOULD TAKE PLACE IN THE LATE MORNING TO EARLY
AFTERNOON. NORTHWEST WINDS WILL BECOME LIGHT NORTHERLY TONIGHT AND
INTO TOMORROW. WINDS WILL INCREASE SOME TOMORROW AFTERNOON.

AUTEN
&&

.PREV DISCUSSION...
ISSUED 239 PM CDT WED JUL 1 2009

PRIMARY SHORT-TERM CHALLENGE WILL BE TIMING OF CLEARING TREND
LATE TONIGHT INTO TOMORROW. AFTER THAT...EMPHASIS WILL SHIFT TO
RAIN CHANCES OVER THE UPCOMING HOLIDAY WEEKEND.

18Z SURFACE CHART SHOWS NEARLY STATIONARY FRONTAL BOUNDARY ACROSS
THE TENNESSEE RIVER VALLEY...WITH A MUCH COOLER AND DRIER AIRMASS
FIRMLY IN PLACE ACROSS CENTRAL ILLINOIS. ALOFT...UNSEASONABLY STRONG
LOW PRESSURE CONTINUES TO SPIN OVER THE EASTERN GREAT LAKES...WHILE
NUMEROUS SHORT-WAVES ROTATE AROUND THIS FEATURE THROUGH THE
MIDWEST. AS A RESULT...EXTENSIVE CLOUD COVER EXISTS ACROSS MUCH OF
THE REGION...AS FAR WEST AS THE CENTRAL AND EASTERN SECTIONS OF
IOWA AND MISSOURI.

SHORT TERM...TONIGHT THROUGH SATURDAY

MAIN QUESTION IN THE IMMEDIATE SHORT-TERM IS WHETHER SKIES WILL
CLEAR TONIGHT. MODELS HAVE A GOOD HANDLE ON THE CURRENT MID AND
LOW-LEVEL RH FIELDS...HOWEVER THEIR FORECAST DEPICTIONS OF HOW
THESE FIELDS WILL EVOLVE DO NOT PROVIDE MUCH FORECAST
ASSISTANCE...AS BOTH THE NAM-WRF AND GFS INDICATE A GOOD DEAL OF
MID-LEVEL DRYING BUT SHOW PERSISTENT LOW-LEVEL MOISTURE THROUGH
THE NIGHT. THE CORRESPONDING NUMERIC GUIDANCE SHOWS CONFLICTING
INFORMATION...WITH THE MET KEEPING CONDITIONS CLOUDY AND THE MAV
CLEARING THINGS OUT. STRONG UPPER LOW HAS SHOWN NO INDICATION OF
AN EASTWARD MOVE TODAY AND NEITHER MODEL SUGGESTS MUCH
MOVEMENT/WEAKENING UNTIL THURSDAY MORNING AT THE EARLIEST. WITH
THE LOW REMAINING ESSENTIALLY STATIONARY AND A CONTINUED NORTHERLY
FETCH OVERNIGHT...AM NOT OPTIMISTIC ABOUT CLEARING ANYTIME SOON.
HAVE THEREFORE MAINTAINED A CLOUDY FORECAST THROUGH TONIGHT.

UPPER LOW SLOWLY LIFTS E/NE ON THURSDAY...RESULTING IN
INCREASINGLY ANTICYCLONIC FLOW. AS UPPER/SURFACE HIGH PRESSURE
BUILD IN FROM THE WEST...THINK SKIES WILL PARTIALLY CLEAR FROM
WEST TO EAST THURSDAY MORNING...HOWEVER WITH COLD AIR ALOFT AND
CU-RULE SHOWING STRONGLY NEGATIVE VALUES OVER THE AREA...THINK ANY
MORNING SUNSHINE WILL BE REPLACED BY PLENTY OF DIURNAL AFTERNOON
CLOUDS. DESPITE A GOOD DEAL OF CLOUD COVER...LIGHT WESTERLY WINDS
AND AT LEAST PARTIAL JULY SUNSHINE WILL BOOST HIGH TEMPS SEVERAL
DEGREES HIGHER THAN TODAY. NUMERIC GUIDANCE EXHIBITS A LARGE
SPREAD IN VALUES...WITH SOME SITES SHOWING A 6 TO 12 DEGREE
DIFFERENCE. BASED ON EXPECTED AMOUNT OF SUNSHINE...WILL LEAN
TOWARD THE WARMER MAV NUMBERS...RESULTING IN HIGHS RANGING FROM
THE MIDDLE 70S ACROSS THE WABASH RIVER VALLEY TO AROUND 80 DEGREES
WEST OF THE ILLINOIS RIVER. SKIES WILL RAPIDLY CLEAR OUT AFTER
SUNSET THURSDAY EVENING...AND WITH LIGHT WINDS EXPECTED HAVE
UNDERCUT GUIDANCE BY A FEW DEGREES FOR LOW TEMPS. SHOULD BE
ANOTHER CHILLY NIGHT...WITH LOWS BOTTOMING OUT IN THE UPPER 50S IN
MOST LOCATIONS.

AS UPPER LOW MOVES FURTHER AWAY...RIDGING WILL TEMPORARILY TAKE
HOLD ACROSS THE MIDWEST ON FRIDAY. WITH MOSTLY SUNNY SKIES
EXPECTED...HIGHS WILL QUICKLY REBOUND INTO THE LOWER TO MIDDLE
80S. STRONG SHORT-WAVE IS PROGGED TO RIDE UP AND OVER THE CREST
OF THE RIDGE LATE FRIDAY...RESULTING IN MCS DEVELOPMENT OVER PARTS
OF THE PLAINS STATES FRIDAY EVENING. CONVECTIVE COMPLEX WILL THEN
TRACK E/SE ALONG AND NORTH OF STATIONARY FRONTAL BOUNDARY
STRETCHING FROM CENTRAL MISSOURI INTO KENTUCKY. MODELS STILL IN
DISAGREEMENT WITH THE EXACT TRACK OF THE MCS...WITH THE 12Z ECMWF
CONTINUING TO BE FURTHER NORTH THAN THE GFS/NAM-WRF. LATEST RUN OF THE
GFS HAS SHIFTED THE RAIN BAND SLIGHTLY FURTHER NORTH THAN ITS
PREVIOUS RUNS...BUT NOT AS FAR NORTH AS THE ECMWF. NAM-WRF
SUPPORTS THE GFS...WHILE CANADIAN RESEMBLES THE ECMWF. GIVEN
UNFAVORABLE UPPER FLOW TO BRING FOCUSING FRONTAL BOUNDARY FURTHER
NORTH...WILL FOLLOW THE MORE SOUTHERN GFS/NAM-WRF SOLUTION.
RESULTING HEAVIEST RAIN AXIS WILL SET UP FROM NORTHERN MISSOURI
E/SE INTO SOUTH-CENTRAL ILLINOIS LATE FRIDAY NIGHT INTO SATURDAY
MORNING. HAVE THEREFORE INCREASED POPS SUBSTANTIALLY FRIDAY
NIGHT...RANGING FROM 30S ALONG AND NORTH OF I-74 TO 50S ACROSS THE
S/SW ZONES.

ONCE MCS ROLLS THROUGH SATURDAY MORNING...BEST PRECIP CHANCES WILL
LIKELY SHIFT FURTHER SOUTH SATURDAY AFTERNOON/EVENING...AS PRIMARY
OUTFLOW GETS SHUNTED INTO MISSOURI/WESTERN KENTUCKY. HOWEVER...WITH
SYNOPTIC FRONT NEARBY AND SMALLER OUTFLOW BOUNDARIES LEFT
BEHIND FROM MORNING CONVECTION...THINK CHANCE POPS STILL HAVE TO
BE MENTIONED FOR THE EVENING OF JULY 4. WILL ONLY CARRY 20 POPS
ACROSS MUCH OF THE AREA...WITH 30S ACROSS THE SOUTH.

LONG TERM...SUNDAY THROUGH WEDNESDAY

THE EXTENDED FORECAST WILL FEATURE NEAR NORMAL TEMPS AND BELOW
NORMAL PRECIP...AS ZONAL FLOW DOMINATES MUCH OF THE CONUS. 12Z
ECMWF SUGGESTS ANOTHER DEEP UPPER LOW DEVELOPING OVER THE EASTERN
GREAT LAKES EARLY IN THE PERIOD THEN MIGRATING S/SW INTO THE DEEP
SOUTH BY THE END OF THE WEEK...BUT THIS SOLUTION HAS BEEN
REJECTED. WILL STICK WITH THE GFS...WHICH INDICATES SLOWLY WARMING
TEMPS SUNDAY THROUGH WEDNESDAY. A WEAK DISTURBANCE MAY BRING A FEW
SHOWERS INTO THE AREA ON MONDAY...BUT HAVE LEFT OUT OF THE
FORECAST FOR NOW PENDING SUPPORT FROM ADDITIONAL MODEL RUNS.

BARNES

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

000
FXUS63 KLOT 012311
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
611 PM CDT WED JUL 1 2009

.DISCUSSION...
310 PM CDT

ONE WOULD CERTAINLY NOT GUESS JULY 1ST IF SHOWN THE CURRENT WATER
VAPOR SATELLITE LOOP OR A 500 HPA HEIGHT ANALYSIS. A QUICK BUT
TEMPORARY SWITCH TO DOGS DAYS OF SUMMER TYPE WX LAST WEEK BUT
LAST FEW DAYS THE WE HAVE GONE RIGHT BACK TO TYPICAL FOR THIS YEAR
ATYPICALLY AMPLIFIED AND ACTIVE UPPER PATTERN DROPPING US WELL
BACK BELOW NORMAL TEMPERATURE WISE. SOLID CLOUD COVER AND A BIT OF
A BREEZE OUT OF THE NW JUST ADDING TO COOL FALLISH FEEL.

SLOW DE-AMPLIFICATION OF PATTERN OVER WESTERN AND CENTRAL NOAM
BEGINNING OVERNIGHT AND CARRYING ON INTO THE HOLIDAY WEEKEND WILL
ALLOW TEMPS TO MODERATE TO NEAR IF NOT TO NORMAL DAYTIME MAXIMA IN
LOWER AND MID 80S.

SLUGGISH UPPER PATTERN WITH UPPER ANTICYCLONE PARKED OVER THE
CANADIAN MARITIMES PREVENTING CENTRAL/LOWER GREAT LAKES UPPER LOW
FROM MAKING ANY SIGNIFICANT PROGRESS E OR NE...WHILE RIDGE OVER
THE ROCKIES AND HIGH PLAINS MAINTAINS NNW TO NW FLOW FROM THE UPPER
MIDWEST TO THE OH VALLEY.

MAIN RA AREA REMAINS ASSOCIATED WITH THE MID LEVEL LOW OVER LOWER
MI WHILE MINOR IMPULSES ROTATING AROUND IT OCCASIONALLY SWING
SCATTERED LIGHT SHOWERS AROUND THE REGION. ONE OF THESE CURRENTLY
DROPPING OUT OF SE WI OVER NORTHERN IL THO ONLY TRACE TO A COUPLE
HUNDREDTHS OF RA DETECTED FROM THESE -SHRA. THESE TO PASS BY THE
LOCAL FORECAST AREA DURING THE REST OF THE AFTERNOON.

WITH ONLY SLOW MOVEMENT OF MID-UPPER LOW TO THE NE OVERNIGHT
EXPECT WIDESPREAD CLOUDINESS TO REMAIN AS BACK EDGE STILL ACROSS N
CENTRAL AND SE MN AS WELL AND EASTERN IA. THERE HAD BEEN ANOTHER
AREA OF SCATTERED -SHRA AROUND THE DOOR CO AND BAY OF GREEN BAY
AREA AS ANOTHER IMPULSE DROPPED DOWN THE W SIDE OF THE UPPER
CIRCULATION BUT AT LEAST ACCORDING TO RADAR HAVE PRETTY MUCH
DRIED UP. THE DISTURBANCE THAT WAS GENERATING THESE -SHRA WILL
START TO TURN TO THE SE AND WITH CENTER OF MAIN CIRCULATION
GRADUALLY BEGINNING TO SHIFT A LITTLE TO THE E AND NE WOULD EXPECT
IF ANY -SHRA REDEVELOP TONIGHT THEY WILL PASS OVER SOUTHERN LAKE
MI AND MISS NE IL THO HAVE HELD ON TO A TOKEN SLIGHT CHC POP VALUE
FOR NW IND THRU 06Z TONIGHT.

BY LATER IN THE DAY THU THE CENTER OF THE UPPER LOW SHIFT TO OVER
SOUTHERN ONTARIO AS STRONG SHORT WAVE CURRENTLY BOTTOMING THE
WESTERN CANADA UPPER LOW EJECTS ACROSS THE SOUTHERN CANADIAN
PRAIRIE. THIS INDUCES RIDGING DOWNSTREAM OVER THE UPPER MS VALLEY
AND SKIES SHOULD BE CLEARING WITH TIME FROM W TO E. THIS SHORT
WAVE PROGGED TO FORM ANOTHER CLOSED LOW OVER CENTRAL ONTARIO BY
FRI MORNING AND THEN DROP TO SOUTHERN QUEBEC BY LATE FRI NIGHT.

THIS MAINTAINS A WNW UPPER FLOW ACROSS THE REGION BUT ALLOWS MILDER
AIR ALREADY IN PLACE ACROSS THE PLAINS N INTO S CENTRAL CANADA TO
BEGIN TO SHIFT E OVER THE UPPER AND MID MS VALLEY AND MODERATING
TEMPERATURES.

ON THE MIND OF MOST IS HOW HOLIDAY WEEKEND LOOKS. LONGER RANGE
MODEL OUTPUT SHOW A SLOW MOVING SURFACE WAVE MOVING E OUT OF THE
CENTRAL PLAINS AS THE IMPULSE CURRENTLY SEEN OVER THE PACIFIC AT
130W 27N EVENTUALLY PUSHES THRU THE UPPER RIDGE OVER THE
ROCKIES...AND COMES OUT OVER THE CENTRAL PLAINS ON FRI. IT THEN
SLOWLY MOVES ESE AS IT TRANSITIONS FROM THE UPPER RIDGE INTO THE
UPPER TROF PROGGED OVER EASTERN CANADA AND THE EASTERN US. HAVE
LOW CHANCE POPS FOR THE FAR SW AND SOUTHERN COUNTIES OF THE LOCAL
FA FRI NIGHT AND SAT AS THE SFC LOW PASSES ACROSS CENTRAL IL
TOWARD THE LOWER OH VALLEY. THEREAFTER...REST OF WEEKEND AND
EARLY NEXT WEEK LOOKS DRY WITH SEASONAL TEMPS BUT COOLER NEAR THE
LAKE SAT...SUN...MON WITH SFC HI SETTLING OVER THE GREAT LAKES.

TRS

&&

.AVIATION...

0000 UTC TAFS...

LARGE UPPER LOW CONTINUES TO SPIN SLOWLY EAST ACROSS THE EASTERN
GREAT LAKES THIS EVENING...WITH ASSOCIATED MVFR STRATOCU DECK
ROTATING AROUND IT.  JUST A FEW SPRINKLES WERE REPORTED EARLIER
TODAY...AND SAVE FOR AN OCCASIONAL ASOS VIRGA REPORT...THERE IS
REALLY NOT MUCH IN THE WAY OF PRECIPITATION REPORTED WITH THIS CLOUD
DECK. CIGS HAVE BOUNCED AROUND A BIT THIS AFTERNOON BETWEEN MVFR
AND VFR...BUT WITH A WEAK SHORTWAVE MAKING ITS WAY SOUTH INTO THE
AREA TONIGHT...WOULD EXPECT MVFR TO BE QUITE COMMON OVERNIGHT INTO
TOMORROW MORNING...THOUGH BRIEF PERIODS OF LOW VFR WILL BE
POSSIBLE. ALSO COULDN`T RULE OUT A WIDELY SCATTERED...VERY LIGHT
SHOWER TONIGHT...BUT CHANCES ARE MUCH TOO SMALL FOR MENTION. AS
SUCH...HAVE MAINTAINED A DRY TAF FOR ALL TERMINALS. WINDS SHOULD
SHOW LITTLE VARIATION IN THE NEAR TERM...WITH THE SLOW MOVING
SYNOPTIC PATTERN EXPECTED TO KEEP SURFACE WINDS FROM THE NORTHWEST
THROUGH THE FIRST HALF OF THURSDAY. BY MIDDAY THURSDAY...THE UPPER
LOW SHOULD FINALLY MAKE ITS WAY FAR ENOUGH EAST FOR SKIES TO BREAK
UP SOMEWHAT AND LIFT INTO VFR. HIGH PRESSURE AT THE SURFACE IS
EXPECTED TO MOVE SOUTH DOWN THE MISSISSIPPI VALLEY ON
THURSDAY...RESULTING IN A GRADUAL SHIFT IN WINDS FROM NORTH TO
WEST LATE IN THE TAF PERIOD.

BOXELL

&&

.MARINE...
250 PM CDT

DEEP UPPER LEVEL CUT OFF LOW CONTINUES TO SPIN NEAR LAKE HURON
MORE TYPICAL OF OCTOBER THAN JULY. BROAD CYCLONIC FLOW ASSOCIATED
WITH THIS LOW WILL PERSIST AT THE SURFACE THROUGH THURSDAY AS THE LOW
ONLY SLOWLY WEAKENS. AS HEIGHTS BUILD ALOFT... THE SURFACE AND
BOUNDARY LAYER FLOW WILL BECOME MORE NEUTRAL AS WEAK SURFACE
RIDGING BUILDS INTO THE AREA FROM THE WEST. THE UPPER CUT OFF LOW
FINALLY OPENS INTO A WAVE LATE THURSDAY AND THEN DRIFTS EAST
FRIDAY ALLOWING A WEAK SURFACE RIDGE TO MOVE OVERHEAD.

AFOREMENTIONED WEAK RIDGE WILL BRING LIGHT WINDS TO LAKE MICHIGAN
THURSDAY NIGHT THROUGH FRIDAY INTO SATURDAY. ANOTHER UPPER LEVEL
LOW DIVES SOUTHEAST INTO THE EASTERN GREAT LAKES ON SATURDAY
HELPING TO MAINTAIN A WEAK NORTHWEST FLOW ALOFT OVER THE REGION
THROUGH THE REMINDER OF THE HOLIDAY WEEKEND. THIS ALLOWS FOR A
CONTINUED WEAK SURFACE GRADIENT PATTERN YIELDING LIGHT WINDS
THROUGHOUT THE PERIOD OVER THE WATER.

ED F

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

000
FXUS63 KILX 012257
AFDILX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
557 PM CDT WED JUL 1 2009

.DISCUSSION...
ISSUED 239 PM CDT WED JUL 1 2009

PRIMARY SHORT-TERM CHALLENGE WILL BE TIMING OF CLEARING TREND
LATE TONIGHT INTO TOMORROW. AFTER THAT...EMPHASIS WILL SHIFT TO
RAIN CHANCES OVER THE UPCOMING HOLIDAY WEEKEND.

18Z SURFACE CHART SHOWS NEARLY STATIONARY FRONTAL BOUNDARY ACROSS
THE TENNESSEE RIVER VALLEY...WITH A MUCH COOLER AND DRIER AIRMASS
FIRMLY IN PLACE ACROSS CENTRAL ILLINOIS. ALOFT...UNSEASONABLY STRONG
LOW PRESSURE CONTINUES TO SPIN OVER THE EASTERN GREAT LAKES...WHILE
NUMEROUS SHORT-WAVES ROTATE AROUND THIS FEATURE THROUGH THE
MIDWEST. AS A RESULT...EXTENSIVE CLOUD COVER EXISTS ACROSS MUCH OF
THE REGION...AS FAR WEST AS THE CENTRAL AND EASTERN SECTIONS OF
IOWA AND MISSOURI.

SHORT TERM...TONIGHT THROUGH SATURDAY

MAIN QUESTION IN THE IMMEDIATE SHORT-TERM IS WHETHER SKIES WILL
CLEAR TONIGHT. MODELS HAVE A GOOD HANDLE ON THE CURRENT MID AND
LOW-LEVEL RH FIELDS...HOWEVER THEIR FORECAST DEPICTIONS OF HOW
THESE FIELDS WILL EVOLVE DO NOT PROVIDE MUCH FORECAST
ASSISTANCE...AS BOTH THE NAM-WRF AND GFS INDICATE A GOOD DEAL OF
MID-LEVEL DRYING BUT SHOW PERSISTENT LOW-LEVEL MOISTURE THROUGH
THE NIGHT. THE CORRESPONDING NUMERIC GUIDANCE SHOWS CONFLICTING
INFORMATION...WITH THE MET KEEPING CONDITIONS CLOUDY AND THE MAV
CLEARING THINGS OUT. STRONG UPPER LOW HAS SHOWN NO INDICATION OF
AN EASTWARD MOVE TODAY AND NEITHER MODEL SUGGESTS MUCH
MOVEMENT/WEAKENING UNTIL THURSDAY MORNING AT THE EARLIEST. WITH
THE LOW REMAINING ESSENTIALLY STATIONARY AND A CONTINUED NORTHERLY
FETCH OVERNIGHT...AM NOT OPTIMISTIC ABOUT CLEARING ANYTIME SOON.
HAVE THEREFORE MAINTAINED A CLOUDY FORECAST THROUGH TONIGHT.

UPPER LOW SLOWLY LIFTS E/NE ON THURSDAY...RESULTING IN
INCREASINGLY ANTICYCLONIC FLOW. AS UPPER/SURFACE HIGH PRESSURE
BUILD IN FROM THE WEST...THINK SKIES WILL PARTIALLY CLEAR FROM
WEST TO EAST THURSDAY MORNING...HOWEVER WITH COLD AIR ALOFT AND
CU-RULE SHOWING STRONGLY NEGATIVE VALUES OVER THE AREA...THINK ANY
MORNING SUNSHINE WILL BE REPLACED BY PLENTY OF DIURNAL AFTERNOON
CLOUDS. DESPITE A GOOD DEAL OF CLOUD COVER...LIGHT WESTERLY WINDS
AND AT LEAST PARTIAL JULY SUNSHINE WILL BOOST HIGH TEMPS SEVERAL
DEGREES HIGHER THAN TODAY. NUMERIC GUIDANCE EXHIBITS A LARGE
SPREAD IN VALUES...WITH SOME SITES SHOWING A 6 TO 12 DEGREE
DIFFERENCE. BASED ON EXPECTED AMOUNT OF SUNSHINE...WILL LEAN
TOWARD THE WARMER MAV NUMBERS...RESULTING IN HIGHS RANGING FROM
THE MIDDLE 70S ACROSS THE WABASH RIVER VALLEY TO AROUND 80 DEGREES
WEST OF THE ILLINOIS RIVER. SKIES WILL RAPIDLY CLEAR OUT AFTER
SUNSET THURSDAY EVENING...AND WITH LIGHT WINDS EXPECTED HAVE
UNDERCUT GUIDANCE BY A FEW DEGREES FOR LOW TEMPS. SHOULD BE
ANOTHER CHILLY NIGHT...WITH LOWS BOTTOMING OUT IN THE UPPER 50S IN
MOST LOCATIONS.

AS UPPER LOW MOVES FURTHER AWAY...RIDGING WILL TEMPORARILY TAKE
HOLD ACROSS THE MIDWEST ON FRIDAY. WITH MOSTLY SUNNY SKIES
EXPECTED...HIGHS WILL QUICKLY REBOUND INTO THE LOWER TO MIDDLE
80S. STRONG SHORT-WAVE IS PROGGED TO RIDE UP AND OVER THE CREST
OF THE RIDGE LATE FRIDAY...RESULTING IN MCS DEVELOPMENT OVER PARTS
OF THE PLAINS STATES FRIDAY EVENING. CONVECTIVE COMPLEX WILL THEN
TRACK E/SE ALONG AND NORTH OF STATIONARY FRONTAL BOUNDARY
STRETCHING FROM CENTRAL MISSOURI INTO KENTUCKY. MODELS STILL IN
DISAGREEMENT WITH THE EXACT TRACK OF THE MCS...WITH THE 12Z ECMWF
CONTINUING TO BE FURTHER NORTH THAN THE GFS/NAM-WRF. LATEST RUN OF THE
GFS HAS SHIFTED THE RAIN BAND SLIGHTLY FURTHER NORTH THAN ITS
PREVIOUS RUNS...BUT NOT AS FAR NORTH AS THE ECMWF. NAM-WRF
SUPPORTS THE GFS...WHILE CANADIAN RESEMBLES THE ECMWF. GIVEN
UNFAVORABLE UPPER FLOW TO BRING FOCUSING FRONTAL BOUNDARY FURTHER
NORTH...WILL FOLLOW THE MORE SOUTHERN GFS/NAM-WRF SOLUTION.
RESULTING HEAVIEST RAIN AXIS WILL SET UP FROM NORTHERN MISSOURI
E/SE INTO SOUTH-CENTRAL ILLINOIS LATE FRIDAY NIGHT INTO SATURDAY
MORNING. HAVE THEREFORE INCREASED POPS SUBSTANTIALLY FRIDAY
NIGHT...RANGING FROM 30S ALONG AND NORTH OF I-74 TO 50S ACROSS THE
S/SW ZONES.

ONCE MCS ROLLS THROUGH SATURDAY MORNING...BEST PRECIP CHANCES WILL
LIKELY SHIFT FURTHER SOUTH SATURDAY AFTERNOON/EVENING...AS PRIMARY
OUTFLOW GETS SHUNTED INTO MISSOURI/WESTERN KENTUCKY. HOWEVER...WITH
SYNOPTIC FRONT NEARBY AND SMALLER OUTFLOW BOUNDARIES LEFT
BEHIND FROM MORNING CONVECTION...THINK CHANCE POPS STILL HAVE TO
BE MENTIONED FOR THE EVENING OF JULY 4. WILL ONLY CARRY 20 POPS
ACROSS MUCH OF THE AREA...WITH 30S ACROSS THE SOUTH.

LONG TERM...SUNDAY THROUGH WEDNESDAY

THE EXTENDED FORECAST WILL FEATURE NEAR NORMAL TEMPS AND BELOW
NORMAL PRECIP...AS ZONAL FLOW DOMINATES MUCH OF THE CONUS. 12Z
ECMWF SUGGESTS ANOTHER DEEP UPPER LOW DEVELOPING OVER THE EASTERN
GREAT LAKES EARLY IN THE PERIOD THEN MIGRATING S/SW INTO THE DEEP
SOUTH BY THE END OF THE WEEK...BUT THIS SOLUTION HAS BEEN
REJECTED. WILL STICK WITH THE GFS...WHICH INDICATES SLOWLY WARMING
TEMPS SUNDAY THROUGH WEDNESDAY. A WEAK DISTURBANCE MAY BRING A FEW
SHOWERS INTO THE AREA ON MONDAY...BUT HAVE LEFT OUT OF THE
FORECAST FOR NOW PENDING SUPPORT FROM ADDITIONAL MODEL RUNS.

BARNES
&&

.AVIATION...
ISSUED 557 PM CDT WED JUL 1 2009

CYCLONIC FLOW CONTINUES OVER THE AREA AND WILL KEEP CLOUDS OVER
ALL TAF SITES REMAINDER OF THE NIGHT AND INTO TOMORROW MORNING.
SPI SHOULD BEGIN TO CLEAR FIRST AS THE UPPER LVL LOW LIFTS
NORTHEAST TOMORROW...FOLLOWED BY DEC...AND THEN PIA...BMI AND CMI.
SCATTERING OUT SHOULD TAKE PLACE IN THE LATE MORNING TO EARLY
AFTERNOON. NORTHWEST WINDS WILL BECOME LIGHT NORTHERLY TONIGHT AND
INTO TOMORROW. WINDS WILL INCREASE SOME TOMORROW AFTERNOON.

AUTEN
&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$