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000
FXUS65 KCYS 230431 AAA
AFDCYS
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHEYENNE WY
931 PM MST SUN NOV 22 2009
.UPDATE...TONIGHT...
FORECAST CONTINUES TO BE ON TRACK FOR THE OVERNIGHT WITH SNOW
SHOWERS EXPECTED TO INCREASE ACROSS THE WESTERN ZONES AND THE
HIGHER TERRAIN ACROSS THE SOUTHERN PORTION OF THE AREA. UP-VALLEY
FLOW NORTHWEST THROUGH THE NORTH PLATTE RIVER VALLEY THIS EVENING
HAS CAUSING INCREASED RADAR RETURNS WITH SOME SPRINKLES TURNING TO
FLURRIES LIKELY OCCURRING TO THE SOUTHEAST OF GLENDO. FIRST BAND
OF SNOW SHOWERS CREATED IFR CONDITIONS IN RAWLINS...BUT HAS SINCE
GENERALLY WEAKENED AND SHIFTED EAST. ANOTHER BAND OF SNOW SHOWERS
HAS BEEN CREATING SIGNIFICANTLY REDUCED VISIBILITIES IN SWEETWATER
COUNTY AND THIS ACTIVITY WILL MOVE INTO CARBON COUNTY BY 1000 PM
MST...SO HAVE INCREASED PRECIPITATION CHANCES TO 100 PERCENT IN
THE HIGHER TERRAIN OF THE SNOWY AND SIERRA MADRE RANGES...AND ALSO
INCREASED PRECIPITATION CHANCES ACROSS CARBON COUNTY. SNOWFALL
AMOUNTS OF 4 TO 6 INCHES IN THE SNOWY RANGE AND SIERRA MADRE ARE
STILL EXPECTED BY MIDDAY MONDAY. 1 TO 2 INCHES OF SNOW CAN BE
EXPECTED BY MIDDAY MONDAY AT LOWER ELEVATIONS OF CARBON AND ALBANY
COUNTY. AN INCH OR LESS IS EXPECTED ELSEWHERE FROM THIS QUICKLY
PASSING STORM SYSTEM.
THE BEST SUPPORT FOR WIDESPREAD SNOW SHOWERS CONTINUES TO BE AT
THE SOUTHERN EXTENT OF THE UPPER WAVE MOVING INTO THE NORTHERN
PLAINS...AND THIS IS THE AREA OF POSITIVE VORTICITY ADVECTION SET
TO MOVE ACROSS THE FORECAST AREA TONIGHT. THE FORECAST AREA WILL
ALSO BE UNDER THE INFLUENCE OF THE FAVORABLE LEFT EXIT REGION OF
A JET STREAK...HELPING TO AMPLIFY THE UPPER TROUGH...EARLY THIS
MORNING AND CHANCES FOR PRECIPITATION DIMINISH MONDAY AFTERNOON
WITH BREEZY NORTHWEST WINDS EAST OF THE LARAMIE RANGE...AND
GENERALLY WEST WINDS WEST OF THE LARAMIE RANGE...CONTINUING
THROUGH THE DAY.
&&
.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...
CLIPPER SYSTEM WILL SWEEP SSE THROUGH NORTHERN PLAINS TUE NIGHT
AND INTO THE CENTRAL PLAINS ON WED. THIS WILL CAUSE FLOW ALOFT
OVER THE CWA TO VEER TO NNW. BACKDOOR COLD FRONT WILL PUSH SOUTH
ACROSS MAINLY THE EASTERN HALF OF CWA TUE NIGHT AND UPSLOPE LOW
CLOUDS WILL LIKELY DEVELOP. HOWEVER...ONLY A FEW FLURRIES ARE
EXPECTED MAINLY OVER NORTHERN PARTS OF CWA TUE NIGHT/WED MORNING.
ALTHOUGH CLOUDS WILL DECREASE WED AFTERNOON...TEMPS WILL BE COOL.
STRONG UPPER RIDGE BUILDS IN FROM THE WEST FOR TURKEY DAY AND
FRIDAY FOR DRY AND WARMER CONDITIONS. A COLD FRONT WILL MOVE
ACROSS THE CWA FRIDAY NIGHT THOUGH...ENDING THE BRIEF WARM UP.
PER HPC...THE UPPER AIR DETAILS FOR THE WEEKEND ARE STILL IFFY AT
THIS POINT WITH GFS AND ECMWF SHOWING RESOLUTION DIFFERENCES.
WILL CONTINUE THE IDEA OF COOLER TEMPS BOTH SATURDAY AND SUNDAY WITH
SOME SNOW SHOWERS MAINLY OVER WESTERN AND NORTHERN PARTS OF CWA.
&&
.AVIATION...
PACIFIC COLD FRONT HAS CONTINUED TO MOVE EAST-SOUTHEAST ACROSS THE
CWA THIS EVENING WITH PERIODS OF SNOW SHOWERS NEAR RAWLINS AND IN
THE SNOWY AND SIERRA MADRE RANGES. CLOUDS WILL CONTINUE TO LOWER
BEHIND THE FRONT WITH MVFR CEILINGS AND VSBYS IN LIGHT SNOW OVER
THE SOUTHERN CWA FROM LATE THIS EVENING THROUGH SUNRISE MONDAY.
SNOW SHOWERS AND STRONG NNW WINDS WILL PREVAIL ESPECIALLY OVER THE
EASTERN HALF OF THE CWA ON MONDAY...WITH AREAS OF MVFR CEILINGS
AND VSBYS. WINDS WILL DECREASE AND SNOW SHOWERS END MONDAY NIGHT
WITH VFR CONDITIONS RETURNING.
&&
.FIRE WEATHER...
COOL TEMPERATURES AND HIGH HUMIDITIES WILL CONTINUE THROUGH THE
MIDDLE OF THE WEEK WITH SCATTERED SNOW SHOWERS INTO MONDAY
EVENING. THEREFORE...NO FIRE WEATHER CONCERNS AT THIS TIME.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&
$$
SHORT TERM...SJC
AVIATION...SJC/TJT
LONG TERM...JLH
FIRE WEATHER...TJT
000
FXUS65 KCYS 222244
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
344 PM MST SUN NOV 22 2009
.SHORT TERM...TONIGHT THROUGH TUESDAY...CURRENT SATELLITE LOOP
SHOWS MOSTLY CLEAR SKIES OVER THE ERN HALF OF THE FORECAST
AREA...WITH CLOUDS MOVING INTO CNTRL AND SRN WYOMING AHEAD OF THE
NEXT UPPER LEVEL TROUGH AND ASSOCIATED COLD FRONT. MODELS SHOW
THIS TROUGH PUSHING INTO THE AREA THIS EVENING WITH SNOW
DEVELOPING ALONG I80 AND GRADUALLY MOVING EASTWARD INTO THE I25
CORRIDOR TONIGHT. NOT MUCH DYNAMIC SUPPORT WITH THIS SYSTEM...BUT GFS
AND NAM SHOW LLVL INSTABILITY WITH LI/S BETWEEN 1C TO 3C TONIGHT
AND EARLY MONDAY. LLVL INSTABILITY COMBINED WITH UPSLOPE FLOW WILL
RESULT IN LIGHT TO MODERATE SNOW ACCUMULATIONS IN THE MOUNTAINS
THROUGH MONDAY MORNING. LITTLE SNOWFALL IS EXPECTED IN THE LOWER
ELEVATIONS OF WYOMING AND THE NEBRASKA PANHANDLE...WITH GENERALLY
A DUSTING TO 1 INCH OF SNOW BELOW 8000 FEET BY NOON MONDAY.
HOWEVER...DUE TO THE SHOWERY NATURE OF THE PRECIP...SOME SNOW
BANDS/SNOW SHOWER MAY PRODUCE BRIEF LOCALLY HEAVY SNOWFALL WITH
LOCAL SNOW AMOUNTS AROUND 2 INCHES POSSIBLE. EXPECT 3 TO 6 INCHES
OF SNOW IN THE MOUNTAINS...WHICH SHOULD BE BELOW ADVISORY
CRITERIA...MAINLY DUE TO THE PROGRESSIVE NATURE OF THE SYSTEM.
MODEL ALSO SHOW 700MB TEMPS LOWERING TO -10C TO -14C ACROSS THE
AREA FOR TOMORROW...RESULTING IN BELOW NORMAL TEMPS AND HIGHS
GENERALLY IN THE UPPER 20S TO UPPER 30S...WITH SOME LOW 40S FOR
HIGHS ACROSS THE NEBRASKA PANHANDLE TOMORROW. THE ONLY MINOR
FORECAST CONCERN IS A SURFACE LOW DEVELOPING ACROSS OKLAHOMA AND
KANSAS TOMORROW...WITH MODELS SHOWING A WRAP AROUND DEFORMATION
SNOW BAND DEVELOPING ACROSS NEBRASKA AND NRN KANSAS AND PUSHING
NORTHEAST. IF THE SURFACE LOW DEVELOPS SLIGHTLY FURTHER NORTH AND
WEST...LIGHT ACCUMULATING SNOWFALL IS POSSIBLE ACROSS SIDNEY AND
ALLIANCE INTO MONDAY EVENING. FOR NOW...INCREASED POP BETWEEN 30
TO 40 PCT ACROSS THE NE PANHANDLE...AND UP TO 90 PCT IN THE
MOUNTAINS OF SRN WYOMING.
UPPER LEVEL TROUGH IS EXPECTED TO PUSH EAST OF THE AREA INTO THE
GREAT PLAINS AND GREAT LAKES REGION BY TUESDAY...WITH LOW TEMPS IN
THE SINGLE DIGITS AND TEENS ACROSS WYOMING...AND TEENS AND 20S
ACROSS THE NEBRASKA PANHANDLE. SKIES WILL BECOME PARTLY CLOUDY
TUESDAY AFTERNOON WITH HIGHS IN THE UPPER 30S TO UPPER 40S EAST OF
THE LARAMIE RANGE...AND MID 20S TO MID 30S ACROSS CARBON AND
ALBANY COUNTIES.
.LONG TERM...TUESDAY NIGHT THROUGH SUNDAY...
CLIPPER SYSTEM WILL SWEEP SSE THROUGH NORTHERN PLAINS TUE NIGHT
AND INTO THE CENTRAL PLAINS ON WED. THIS WILL CAUSE FLOW ALOFT
OVER THE CWA TO VEER TO NNW. BACKDOOR COLD FRONT WILL PUSH SOUTH
ACROSS MAINLY THE EASTERN HALF OF CWA TUE NIGHT AND UPSLOPE LOW
CLOUDS WILL LIKELY DEVELOP. HOWEVER...ONLY A FEW FLURRIES ARE
EXPECTED MAINLY OVER NORTHERN PARTS OF CWA TUE NIGHT/WED MORNING.
ALTHOUGH CLOUDS WILL DECREASE WED AFTERNOON...TEMPS WILL BE COOL.
STRONG UPPER RIDGE BUILDS IN FROM THE WEST FOR TURKEY DAY AND
FRIDAY FOR DRY AND WARMER CONDITIONS. A COLD FRONT WILL MOVE
ACROSS THE CWA FRIDAY NIGHT THOUGH...ENDING THE BRIEF WARM UP.
PER HPC...THE UPPER AIR DETAILS FOR THE WEEKEND ARE STILL IFFY AT
THIS POINT WITH GFS AND ECMWF SHOWING RESOLUTION DIFFERENCES.
WILL CONTINUE THE IDEA OF COOLER TEMPS BOTH SATURDAY AND SUNDAY WITH
SOME SNOW SHOWERS MAINLY OVER WESTERN AND NORTHERN PARTS OF CWA.
&&
.AVIATION....PACIFIC COLD FRONT WILL BE MOVING QUICKLY ACROSS CWA
FROM WEST TO EAST THIS EVENING. CLOUDS WILL LOWER OVER THE CWA
BEHIND THE FRONT WITH MVFR CEILINGS AND VSBYS IN LIGHT SNOW OVER
THE SOUTHERN CWA FROM LATE THIS EVENING THROUGH SUNRISE MONDAY.
SNOW SHOWERS AND STRONG NNW WINDS WILL PREVAIL ESPECIALLY OVER THE
EASTERN HALF OF THE CWA ON MONDAY...WITH AREAS OF MVFR CEILINGS
AND VSBYS. WINDS WILL DECREASE AND SNOW SHOWERS END MONDAY NIGHT
WITH VFR CONDITIONS RETURNING.
&&
.FIRE WEATHER...COOL TEMPERATURES AND HIGH HUMIDITIES WILL
CONTINUE THROUGH THE MIDDLE OF THE WEEK WITH SCATTERED SNOW
SHOWERS INTO MONDAY EVENING. THEREFORE...NO FIRE WEATHER CONCERNS
AT THIS TIME.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&
$$
SHORT TERM...TJT
LONG TERM/AVIATION...JLH
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000
FXUS65 KRIW 222156
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
256 PM MST SUN NOV 22 2009
.SHORT TERM...TONIGHT THROUGH WEDNESDAY
QUICK HITTING STORM SYSTEM BRINGING MODERATE SNOW TO PORTIONS OF
WESTERN WYOMING THIS AFTERNOON WITH A QUICK 1 TO 3 INCHES SINCE 11
AM. APPROACHING FRONTAL SYSTEM...QG FORCING...INITIAL DIFFLUENT
FLOW AND NOSE OF CURVED JET STREAK WILL ADD UP TO CONTINUED SNOWFALL
THROUGH THE EVENING...ESPECIALLY WHEN COMBINED WITH STEEPENING LAPSE
RATES TO AT LEAST 7.5C/KM AND LOW LI`S. DEBATED A WINTER WEATHER
ADVISORY FOR THE TETONS AND STAR VALLEY BUT DECIDED TO JUST GIVE A
FEW ADVISORY AMOUNTS TO THE FAVORED AREAS AND FRESHEN UP THE SPS.
UPPER LOW IS STILL HOLDING TOGETHER FAIRLY GOOD AND IT MAY BE A
LITTLE STRONGER EAST OF THE DIVIDE THAN EARLIER EXPECTED. HAVE
TRENDED TOWARDS THE 18Z NAM WITH A BETTER CHANCE OF SNOW IN THE
CENTRAL BASINS AND SURROUNDING MOUNTAINS AFTER MIDNIGHT. ALSO KEPT
IDEA OF GUSTY WINDS BEHIND THE FRONT IN THE WIND RIVER BASIN. SHOULD
ALSO SEE A GOOD QUICK SHOT OF SNOW AND STRONG WIND ALONG THE I80
CORRIDOR THIS EVENING AND HIT THIS AREA A LITTLE HARDER. SOME
LIGHT SNOW OR FLURRIES MAY LINGER EARLY MONDAY IN THE EAST AND IN
THE MOUNTAINS THROUGH THE DAY. STEEP TEMPERATURE INVERSIONS SHOULD
DEVELOP IN THE BASINS AND VALLEYS MONDAY NIGHT AND STICK AROUND
FOR A FEW DAYS. THE MOUNTAINS WILL SEE SOME IMPROVEMENT TUESDAY
INTO WEDNESDAY. THE NEXT CLIPPER TYPE SYSTEM MAY VERY WELL IMPACT
OUR NERN ZONES TUESDAY NIGHT WITH A CHANCE OF SNOW AND GUSTY NORTH
WIND. TIMING LOOKS A LITTLE FASTER THAN EARLIER RUNS AND ADJUSTED
THIS FASTER BY 12 HOURS.
.LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY
WEAK BACKDOOR COLD FRONT MAY BRING SOME LOW CLOUDS AND LIGHT/SNOW
FLURRIES DOWN THE INTERSTATE 25 CORRIDOR WEDNESDAY. OTHERWISE DRY
AND MILD CONDITIONS WILL PREVAIL ACROSS MOST OF THE AREA WEDNESDAY
THROUGH FRIDAY. CHANCES OF SNOW INCREASE ACROSS THE FAR WEST
VALLEYS AND WESTERN MOUNTAINS LATE FRIDAY WITH COOLER CONDITIONS
AND CHANCES FOR LIGHT SNOW SPREADING EAST OF THE DIVIDE SATURDAY.
MAINLY DRY AND COOL WEATHER EXPECTED ON SUNDAY.
MEDIUM-RANGE MODELS REVERTING BACK TO STRONGER CLIPPER SYSTEM DIVING
INTO THE NORTHERN PLAINS TUESDAY NIGHT DRIVING SHALLOW BACK DOOR
COLD FRONT ALONG WITH WEAK ISENTROPIC UPGLIDE ACROSS EASTERN
WYOMING. LOW POPS REINTRODUCED DOWN THE INTERSTATE 25 CORRIDOR
WEDNESDAY EXPECTING POSSIBLY SOME LOW CLOUDS/FLURRIES BEHIND FRONT.
OTHERWISE UPPER RIDGE BUILDS ACROSS REGION WEDNESDAY AND THURSDAY
BRINGING MOSTLY CLEAR SKIES WITH ABOVE NORMAL HIGH TEMPERATURES
THOUGH VALLEY INVERSIONS WILL SUPPRESS HIGHS THANKSGIVING DAY AND
FRIDAY...AND LARGE DIURNAL TEMPERATURE RANGES WITH GOOD RADIATIONAL
COOLING AT NIGHT. MODELS SHOW INCREASING SPREAD WITH NEXT INCOMING
PACIFIC TROUGH MAKING LANDFALL ON FRIDAY. RUN-TO-RUN AGREEMENT
BETWEEN ECMWF AND GFS EXISTS ON A TREND TOWARD SLOWER PROGRESSION.
FORECAST FRIDAY NIGHT AND ONWARD A BLEND OF 00Z ECMWF AND GEFS MEAN
WITH SPLIT TROUGH PASSAGE EXPECTED FRIDAY NIGHT AND
SATURDAY...INCREASING CHANCES OF SNOW ACROSS THE WEST LATE FRIDAY
WITH POST-FRONTAL CHANCES OF SNOW EAST OF THE DIVIDE SATURDAY.
HOWEVER...AS SEEN WITH THE LAST FEW SPLIT SYSTEMS...PRECIPITATION
EAST OF THE DIVIDE HAS BEEN HARD TO COME BY. THUS...IMPACTS TO
TRAVEL OVER THE HOLIDAY WEEKEND EXPECTED OVER THE FAR WEST AND
WESTERN MOUNTAINS FRIDAY NIGHT INTO SATURDAY MORNING THOUGH IMPACTS
EXPECTED TO BE MINIMAL WITH SNOW AMOUNTS BELOW ADVISORY CRITERIA.
MAINLY DRY CONDITIONS EXPECTED ON SUNDAY WITH NEAR NORMAL
TEMPERATURES.
&&
.AVIATION...
A TROUGH WILL MOVE ACROSS WYOMING OVERNIGHT...BRINGING LIGHT SNOW TO
THE WEST AND SOUTH AND POSSIBLY TO THE BIGHORNS AND JOHNSON COUNTY.
EXPECT MVFR CIGS AND VSBYS WITH SNOW...WITH LOCAL IFR CONDITIONS.
THE SNOW WILL TAPER TO SNOW SHOWERS BEFORE 06Z AND MAINLY IMPACTING
HIGHER TERRAIN...THOUGH MVFR CIGS WILL LIKELY PERSIST IN THE FAR
WEST VALLEYS THROUGH LATE MONDAY MORNING. MTN OBSCURATIONS ARE
EXPECTED THROUGH THE OVERNIGHT...IMPROVING SOME AS MONDAY DAYTIME
PROGRESSES. NORTHWEST TO NORTH WINDS ARE EXPECTED OVER THE CENTRAL
AND SOUTHWEST OVERNIGHT AND MONDAY.
&&
.FIRE WEATHER...
A QUICK HITTING STORM SYSTEM WILL MOVE ACROSS THE AREA TONIGHT
SPREADING A ROUND OF SNOW AND GUSTY WIND. THE HEAVIEST SNOW WILL
CONTINUE OUT WEST THIS EVENING BEFORE DIMINISHING. THE ODDS OF
LIGHT SNOW WILL INCREASE EAST OF THE DIVIDE LATER THIS EVENING
AND INTO THE EARLY MORNING HOURS. BRISK NORTH TO NORTHWEST WINDS
AND COLD CONDITIONS WILL PREVAIL IN MANY AREAS MONDAY WITH SOME
FLURRIES IN THE HIGH COUNTRY. STEEP BASIN AND VALLEY INVERSIONS
WILL DEVELOP MONDAY NIGHT WITH GRADUALLY WARMING TEMPERATURES
IN THE MOUNTAINS THROUGH MIDWEEK.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
SHORT TERM...SKRBAC
LONG TERM...AEM
AVIATION...TWB
FIRE WEATHER...SKRBAC
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000
FXUS63 KUNR 222138 RRA
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
238 PM MST SUN NOV 22 2009
.DISCUSSION...21Z SFC ANALYSIS SHOWS A DEEPENING TROUGH ALONG THE
LEE SIDE OF THE ROCKIES IN RESPONSE TO FAST APPROACHING UPPER
TROUGH. IT LOOKS LIKE THERE WILL BE ENOUGH LIFT AND MOISTURE AS THE
TROUGH MOVES INTO THE AREA FOR A FEW SNOW SHOWERS TO REACH THE
GROUND OVERNIGHT.
ON MONDAY...THE UPPER LOW/UPPER TROUGH WILL CROSS THE FORECAST AREA
LEADING TO A SLIGHT CHANCE OF SNOW SHOWERS OR RAIN SHOWERS. THE BEST
CHANCE OF PRECIPITATION WILL BE OVER SOUTH CENTRAL SOUTH DAKOTA
WHERE THE STRONGEST DYNAMICS AND BEST MOISTURE WILL BE AVAILABLE.
BREEZY/WINDY NORTHWEST WINDS WILL DEVELOP DUE TO A TIGHT SFC
PRESSURE GRADIENT BETWEEN THE SOUTHEAST SHIFTING SFC LOW AND HIGH
PRESSURE BUILDING OVER THE NORTHERN ROCKIES.
UPPER RIDGE AXIS THEN MOVES OVER THE AREA LEADING TO DRY WEATHER ON
TUESDAY...BEFORE ANOTHER UPPER TROUGH DROPS ACROSS NORTH DAKOTA AND
INTO THE UPPER MIDWEST. THE TAIL END OF THE TROUGH WILL CREATE A
SLIGHT CHANCE OF SNOW SHOWERS ACROSS NORTHEASTERN WYOMING AND FAR
WESTERN SOUTH DAKOTA ON TUESDAY NIGHT.
EXTENDED...HIGH PRESSURE WILL BUILD ACROSS THE WESTERN CONUS ON
WEDNESDAY AND PUSH ACROSS THE CWA THROUGH THE END OF THE WEEK. THIS
WILL BRING QUIET WEATHER TO THE AREA. AS THE RIDGE AXIS SLIDES OVER
THE CWA THURSDAY INTO FRIDAY...EXPECT HIGH TEMPERATURES TO CLIMB
INTO THE 50S. COLD FRONT WILL SWEEP ACROSS THE AREA LATE ON FRIDAY
AS A TROUGH SWINGS INTO THE PACIFIC NORTHWEST. TROUGH IS EXPECTED TO
MOVE ACROSS THE CWA ON SATURDAY BRINGING A SLIGHT CHANCE OF RAIN AND
SNOW TO NORTHEAST WYOMING AND FAR WESTERN SOUTH DAKOTA. SEVERAL GFS
ENSEMBLE MEMBERS AGREE WITH THIS SCENARIO...SO WILL INTRODUCE POPS
DURING THIS TIME FRAME.
&&
.AVIATION...A FEW AREAS OF LIGHT SNOW MAY DEVELOP THIS EVENING OVER
NORTHEAST WYOMING AND FAR WESTERN SOUTH DAKOTA AS AN UPPER LEVEL
DISTURBANCE AND WEAK COLD FRONT PUSH INTO THE AREA. MOST LOCATIONS
WILL REMAIN VFR...THOUGH SOME LCL MVFR CIGS WILL BE POSSIBLE TONIGHT
OVER THE BLACK HILLS AND HIGHER TERRAIN OF NERN WY.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&
$$
GR/JW
000
FXUS63 KUNR 222138
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
238 AM MST SUN NOV 22 2009
.DISCUSSION...21Z SFC ANALYSIS SHOWS A DEEPENING TROUGH ALONG THE
LEE SIDE OF THE ROCKIES IN RESPONSE TO FAST APPROACHING UPPER
TROUGH. IT LOOKS LIKE THERE WILL BE ENOUGH LIFT AND MOISTURE AS THE
TROUGH MOVES INTO THE AREA FOR A FEW SNOW SHOWERS TO REACH THE
GROUND OVERNIGHT.
ON MONDAY...THE UPPER LOW/UPPER TROUGH WILL CROSS THE FORECAST AREA
LEADING TO A SLIGHT CHANCE OF SNOW SHOWERS OR RAIN SHOWERS. THE BEST
CHANCE OF PRECIPITATION WILL BE OVER SOUTH CENTRAL SOUTH DAKOTA
WHERE THE STRONGEST DYNAMICS AND BEST MOISTURE WILL BE AVAILABLE.
BREEZY/WINDY NORTHWEST WINDS WILL DEVELOP DUE TO A TIGHT SFC
PRESSURE GRADIENT BETWEEN THE SOUTHEAST SHIFTING SFC LOW AND HIGH
PRESSURE BUILDING OVER THE NORTHERN ROCKIES.
UPPER RIDGE AXIS THEN MOVES OVER THE AREA LEADING TO DRY WEATHER ON
TUESDAY...BEFORE ANOTHER UPPER TROUGH DROPS ACROSS NORTH DAKOTA AND
INTO THE UPPER MIDWEST. THE TAIL END OF THE TROUGH WILL CREATE A
SLIGHT CHANCE OF SNOW SHOWERS ACROSS NORTHEASTERN WYOMING AND FAR
WESTERN SOUTH DAKOTA ON TUESDAY NIGHT.
EXTENDED...HIGH PRESSURE WILL BUILD ACROSS THE WESTERN CONUS ON
WEDNESDAY AND PUSH ACROSS THE CWA THROUGH THE END OF THE WEEK. THIS
WILL BRING QUIET WEATHER TO THE AREA. AS THE RIDGE AXIS SLIDES OVER
THE CWA THURSDAY INTO FRIDAY...EXPECT HIGH TEMPERATURES TO CLIMB
INTO THE 50S. COLD FRONT WILL SWEEP ACROSS THE AREA LATE ON FRIDAY
AS A TROUGH SWINGS INTO THE PACIFIC NORTHWEST. TROUGH IS EXPECTED TO
MOVE ACROSS THE CWA ON SATURDAY BRINGING A SLIGHT CHANCE OF RAIN AND
SNOW TO NORTHEAST WYOMING AND FAR WESTERN SOUTH DAKOTA. SEVERAL GFS
ENSEMBLE MEMBERS AGREE WITH THIS SCENARIO...SO WILL INTRODUCE POPS
DURING THIS TIME FRAME.
&&
.AVIATION...A FEW AREAS OF LIGHT SNOW MAY DEVELOP THIS EVENING OVER
NORTHEAST WYOMING AND FAR WESTERN SOUTH DAKOTA AS AN UPPER LEVEL
DISTURBANCE AND WEAK COLD FRONT PUSH INTO THE AREA. MOST LOCATIONS
WILL REMAIN VFR...THOUGH SOME LCL MVFR CIGS WILL BE POSSIBLE TONIGHT
OVER THE BLACK HILLS AND HIGHER TERRAIN OF NERN WY.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&
$$
GR/JW
000
FXUS63 KUNR 221738
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1038 AM MST SUN NOV 22 2009
.DISCUSSION...17Z SFC ANALYSIS SHOWS HIGH PRESSURE OVER
SOUTHWESTERN AND CENTRAL SOUTH DAKOTA WITH A DEEPENING LEE SIDE
TROUGH EAST OF THE NORTHERN ROCKIES. HAVE UPDATED FORECAST TO
RAISE WIND SPEEDS OVER NORTHEASTERN WYOMING AND TO LOWER CLOUD
COVER.
&&
.AVIATION...A FEW AREAS OF LIGHT SNOW MAY DEVELOP THIS EVENING
OVER NORTHEAST WYOMING AND FAR WESTERN SOUTH DAKOTA AS AN UPPER
LEVEL DISTURBANCE AND WEAK COLD FRONT PUSH INTO THE AREA. MOST
LOCATIONS WILL REMAIN VFR...THOUGH SOME LCL MVFR CIGS WILL BE
POSSIBLE TONIGHT OVER THE BLACK HILLS AND HIGHER TERRAIN OF NERN
WY.
&&
.PREV DISCUSSION... /ISSUED 302 AM MST SUN NOV 22 2009/
DISCUSSION...09Z SURFACE ANALYSIS SHOWED COLD FRONT FROM EASTERN
ND INTO SOUTHWEST KS. WEAK RIDGE PUSHING INTO THE CWA. UPPER
TROUGH SLIPPING ACROSS EASTERN PORTIONS OF MT/WY/CO...WITH 90KT
JET STREAK CREATING SOME RETURNS ON KUDX WSR-88D. GIVEN SURFACE
T/TD SPREADS AND 00Z KUNR SOUNDING...LITTLE IF ANYTHING REACHING
GROUND. FOR TODAY...SHORTWAVE RIDGE MOVES OVER THE AREA AS
SURFACE RIDGE SLIPS EAST ALLOWING FOR RETURN FLOW IN THE WEST.
TONIGHT...SECONDARY UPPER TROUGH RACES INTO THE NORTHERN PLAINS
WITH MAIN JET STREAM STARTING TO FORM MAIN WAVE IN SOUTHERN WY/NE.
COULD BE LIGHT PRECIPITATION IN THE WEST.
MONDAY...MODEL CONSENSUS SHOWS UPPER LOW CLOSING OVER SOUTHERN NE.
THIS WILL BRING A CHANCE OF PRECIPITATION TO THE AREA AS IT MOVES
WEST TO EAST. BEST CHANCES WILL BE OVER SOUTH CENTRAL SD WITH BEST
LIFT/FRONTOGENESIS/UPPER LEVEL DIVERGENCE/MOISTURE COMBINE.
SURFACE LOW MOVES FROM THE BLACK HILLS TO IA/SD/NE BORDER.
GRADIENT WILL SUPPORT WINDY AREAS BEHIND THE LOW.
TUESDAY...UPPER RIDGE BUILDS OVER THE WEST AS YET ANOTHER WAVE
DROPS INTO THE UPPER MIDWEST. TAIL END OF WAVE/TROUGH WILL BRING
SMALL CHANCES FOR -SHSN TO THE AREA TUESDAY NIGHT.
EXTENDED...QUIET WEATHER WILL RETURN FOR THE MIDDLE INTO THE END
OF THE WORK WEEK AS AN UPPER LEVEL RIDGE BUILDS OVER THE AREA.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&
$$
000
FXUS65 KRIW 221035
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
335 AM MST SUN NOV 22 2009
.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
CLOUDS ASSOCIATED WITH SATURDAYS SHORTWAVE ARE EXITING TO THE EAST.
A VERY SHORT RESPITE BETWEEN SYSTEMS IS TAKING PLACE BEFORE SNOWFALL
GETS UNDERWAY BY 18Z TODAY IN WESTERN WY FROM ISENTROPIC LIFT AHEAD
OF THE NEXT DIGGING UPSTREAM WEATHER SYSTEM NOW ALONG 130W OFF THE
PACIFIC COAST WITH A VORT MAX LOCATED AT ABOUT 45N. THE ISENTROPIC
LIFT WILL JUST BE FLEETING BUT Q VECTOR FORCING WILL TAKE OVER ALONG
WITH A STRENGTHENING WESTERLY DIFLUENT FLOW WILL KEEP THE SNOWFALL
GOING IN WESTERN WY UNTIL 00Z THIS EVENING BEFORE SNOWFALL DECREASES
IN INTENSITY. MOST OF THE 3 TO 6 INCHES OF SNOWFALL THAT ACCUMULATES
IN WESTERN AND SOUTHWEST WY SHOULD OCCUR BEFORE 00Z. AROUND 1 TO 3
INCHES OF SNOWFALL SHOULD OCCUR IN THE FAR WESTERN VALLEYS WITH AN
INCH OR TWO IN THE UPPER GREEN RIVER BASIN FOOTHILLS. A DRIER
AIRMASS ALONG WITH 50 TO 60 MPH WESTERLY WIND GUSTS SHOULD OCCUR ON
THE EAST SLOPE OF THE WIND RIVER MTNS AS WELL AS OVER THE EASTERN
ABSAROKA MTNS TODAY AS A LEE SIDE WALL CLOUD DEVELOPS OVER THOSE
AREAS. SOUTHWEST WINDS OF 30 TO 40 MPH SHOULD BE COMMON THIS
AFTERNOON FROM THE GREEN MTNS TO CPR AS THE GRADIENT TIGHTENS. TONIGHT THE
ENERGY FROM THE TROUGH WILL TRANSFER TO AREAS EAST OF THE DIVIDE AS
Q VECTOR FORCING SHIFTS EAST AND A CANADIAN COLD FRONT PLOWS SOUTH
ACROSS AREAS EAST OF THE DIVIDE. INSTABILITY SNOW SHOWERS WILL
CONTINUE IN THE WEST SUNDAY NIGHT CONTINUING THROUGH MONDAY MORNING.
LIGHT SNOW SHOWERS WILL CONTINUE INTO MONDAY MORNING EAST OF THE
DIVIDE AND LINGERING IN NATRONA COUNTY THROUGH MONDAY AFTERNOON AS Q
VECTOR FORCING LINGERS THERE AS DOES BOUNDARY LAYER MSTR. CLEARING
WILL TAKE PLACE MONDAY NIGHT AS A 1037MB SURFACE HIGH BUILDS INTO
THE AREA WITH STRONG RADIATIONAL COOLING TAKING PLACE. SHOULD SEE
SOME SUB ZERO TEMPS IN SOME OF THE WESTERN VALLEYS AS WELL ALONG
WITH SOME PATCHY FOG THERE. FOG SHOULD NOT BE WIDESPREAD HOWEVER
WITH THE LACK OF A DRY LAYER ABOVE THE INVERSION. DRY WEATHER ALONG
WITH SEASONABLY COOL WX WILL PREVAIL TUESDAY. ON TUESDAY NIGHT A
BACKDOOR COLD FRONT WILL GIVE JOHNSON COUNTY A GLANCING BLOW IN THE
FORM OF A NORTHERLY WIND SHIFT WITH AN ASSOCIATED CLIPPER TYPE
SYSTEM GIVING THE NORTHERN MTNS SOME ISOLATED SNOW SHOWERS. THE BULK
OF THE ENERGY FROM THIS SYSTEM SHOULD REMAIN IN THE NORTHERN PLAINS
IF ONE AVERAGES OUT THE OSCILLATING SOLNS OF PREVIOUS MODEL RUNS.
.LONG TERM...WEDNESDAY THROUGH SUNDAY
WEAK BACKDOOR COLD FRONT MAY BRING SOME LOW CLOUDS AND LIGHT/SNOW
FLURRIES DOWN THE INTERSTATE 25 CORRIDOR WEDNESDAY. OTHERWISE DRY
AND MILD CONDITIONS WILL PREVAIL ACROSS MOST OF THE AREA WEDNESDAY
THROUGH FRIDAY. CHANCES OF SNOW INCREASE ACROSS THE FAR WEST
VALLEYS AND WESTERN MOUNTAINS LATE FRIDAY WITH COOLER CONDITIONS
AND CHANCES FOR LIGHT SNOW SPREADING EAST OF THE DIVIDE SATURDAY.
MAINLY DRY AND COOL WEATHER EXPECTED ON SUNDAY.
MEDIUM-RANGE MODELS REVERTING BACK TO STRONGER CLIPPER SYSTEM DIVING
INTO THE NORTHERN PLAINS TUESDAY NIGHT DRIVING SHALLOW BACK DOOR
COLD FRONT ALONG WITH WEAK ISENTROPIC UPGLIDE ACROSS EASTERN
WYOMING. LOW POPS REINTRODUCED DOWN THE INTERSTATE 25 CORRIDOR
WEDNESDAY EXPECTING POSSIBLY SOME LOW CLOUDS/FLURRIES BEHIND FRONT.
OTHERWISE UPPER RIDGE BUILDS ACROSS REGION WEDNESDAY AND THURSDAY
BRINGING MOSTLY CLEAR SKIES WITH ABOVE NORMAL HIGH TEMPERATURES
THOUGH VALLEY INVERSIONS WILL SUPPRESS HIGHS THANKSGIVING DAY AND
FRIDAY...AND LARGE DIURNAL TEMPERATURE RANGES WITH GOOD RADIATIONAL
COOLING AT NIGHT. MODELS SHOW INCREASING SPREAD WITH NEXT INCOMING
PACIFIC TROUGH MAKING LANDFALL ON FRIDAY. RUN-TO-RUN AGREEMENT
BETWEEN ECMWF AND GFS EXISTS ON A TREND TOWARD SLOWER PROGRESSION.
FORECAST FRIDAY NIGHT AND ONWARD A BLEND OF 00Z ECMWF AND GEFS MEAN
WITH SPLIT TROUGH PASSAGE EXPECTED FRIDAY NIGHT AND
SATURDAY...INCREASING CHANCES OF SNOW ACROSS THE WEST LATE FRIDAY
WITH POST-FRONTAL CHANCES OF SNOW EAST OF THE DIVIDE SATURDAY.
HOWEVER...AS SEEN WITH THE LAST FEW SPLIT SYSTEMS...PRECIPITATION
EAST OF THE DIVIDE HAS BEEN HARD TO COME BY. THUS...IMPACTS TO
TRAVEL OVER THE HOLIDAY WEEKEND EXPECTED OVER THE FAR WEST AND
WESTERN MOUNTAINS FRIDAY NIGHT INTO SATURDAY MORNING THOUGH IMPACTS
EXPECTED TO BE MINIMAL WITH SNOW AMOUNTS BELOW ADVISORY CRITERIA.
MAINLY DRY CONDITIONS EXPECTED ON SUNDAY WITH NEAR NORMAL
TEMPERATURES.
&&
.AVIATION...EAST OF THE CONTINENTAL DIVIDE VFR CONDITIONS WILL OCCUR TODAY AND
INTO THIS EVENING. WINDY AREAS WILL OCCUR IN EAST CENTRAL WY
INCLUDING THE KCPR AIRPORT WHERE WIND SPEEDS OF 20 TO 30 KNOTS CAN
BE EXPECTED WITH GUSTS TO 40 KNOTS. WEST OF THE DIVIDE CLOUDS WILL
BE INCREASING AND LOWERING FROM 12Z TO 18Z WITH SOME SNOW DEVELOPING
OVER THE WESTERN MOUNTAINS AROUND 18Z. VFR CONDITIONS WILL GIVE WAY
TO MVFR AND IFR CONDITIONS FROM 18Z TO 00Z AS SNOW INCREASES IN
COVERAGE IN WESTERN WY. MOUNTAINS WILL BE OBSCURED. AFTER 00Z MVFR
CONDITIONS WILL PREVAIL IN FAR WEST WY WITH SNOW SHOWERS AND MOUNTAIN
OBSCURATION.
&&
.FIRE WEATHER...SNOWFALL WILL OCCUR IN WESTERN WY TODAY ALONG WITH 3
TO 6 INCHES EXPECTED IN THE MOUNTAINS AND 1 TO 3 INCHES IN THE
VALLEYS. WEST TO SOUTHWEST WINDS WILL INCREASE EAST OF THE DIVIDE
TODAY WITH BRISK WEST WINDS EXPECTED IN SWEETWATER COUNTY TONIGHT.
SOME SNOW WILL SPREAD TO AREAS EAST OF THE DIVIDE TONIGHT AND MONDAY
WITH SNOW SHOWERS CONTINUING IN WESTERN WYOMING TONIGHT AND MONDAY
MORNING. THE AIRMASS WILL BE UNSTABLE TONIGHT. ON MONDAY NIGHT
EXPECT A STRONG NOCTURNAL INVERSION TO FORM.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...LIPSON
LONG TERM...AEM
AVIATION...AR
FIRE WEATHER...LIPSON
000
FXUS65 KCYS 221031
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
331 AM MST SUN NOV 22 2009
.SHORT TERM...TODAY THROUGH MONDAY NIGHT...
CLOUDS HAVE BEEN DECREASING OVER THE EASTERN PART OF THE CWA SINCE
06Z WITH THE PASSAGE OF THE SHORTWAVE TROUGH. AREAS OF LOWER CLOUDS
WITH BASES BETWEEN 3 AND 4 THOUSAND FEET AGL WERE NOTED IN SATELLITE
IMAGERY AND SURFACE OBSERVATIONS EARLY THIS MORNING. MOST OF TODAY
WILL BE QUIET WITH WINDY AREAS NEAR THE MOUNTAINS...SEASONAL
TEMPERATURES AND INCREASING MID AND HIGH CLOUDS. THE NEXT SHORTWAVE
TROUGH WAS LOCATED OVER THE PACIFIC NORTHWEST EARLY THIS MORNING.
THE TIMING OF THE MOVEMENT OF THE FEATURE IS HANDLED SLIGHTLY
DIFFERNTLY BY THE MODELS. THE FEATURE DIGS AND DEEPENS SUNDAY NIGHT
AND MONDAY WITH MODELS CLOSING OFF AN UPPER LOW AND PLACING IT OVER
THE CENTRAL HIGH PLAINS BY 00Z TUESDAY. FOR THIS PART OF THE
FORECAST WILL CONTINUE TO LEAN MORE TOWARD THE ECMWF WHICH HAS BEEN
CONSISTENT AND PREFERED BY HPC. THE 00Z ECMWF IS STILL A BIT
SLOWER THAN THE OTHER MODELS AND IS TRENDING SLIGHTLY SLOWER. THAT
MODEL MOVES THE DEVELOPING UPPER LOW FROM NORTHWEST MONTANA AT 00Z
MONDAY TO NORTHWEST KANSAS AT 00Z TUESDAY. THE UPPER LOW THEN MOVES
EAST MONDAY NIGHT AND DEEPENS OVER THE PLAINS. THE ASSOCIATED
PACIFIC COLD FRONT IS STILL ON TRACK TO MOVE ACROSS THE CWA TONIGHT
WITH A SURFACE LOW FORMING OVER SOUTHEAST COLORADO BETWEEN 06Z AND
12Z MONDAY. BEHIND THE FRONT AND SHORTWAVE TROUGH WILL BE COOLER
TEMPERATURES AND FAIRLY STRONG NORTHERLY WINDS WHICH WILL CONTINUE
THROUGH EARLY MONDAY NIGHT. SNOW WILL ALSO DEVELOP OVER THE CWA
BEHIND THE FRONT AS MID LEVEL FRONTOGENESIS AND UPPER LEVEL
DIVERGENCE INCREASE ALONG WITH THE LEFT EXIT REGION OF THE 300 MB
JET. FORECAST RAOBS ALSO INDICATE A FAIRLY STEEP LAPSE RATE TONIGHT
AND MONDAY OVER THE CWA. THE MORE WIDESPREAD SNOW WILL LIKELY BE
OVER THE MOUNTAINS AND SOUTH PART OF THE CWA. AT THIS TIME...THE
BEST PERIOD FOR THE SNOWFALL WILL BE FROM LATE THIS EVENING THROUGH
12Z MONDAY. FOR NOW WILL PLACE 4 TO 7 INCHES OF SNOW FOR THE SNOWY
RANGE FOR TONIGHT AND MONDAY MORNING...WITH 1 TO 2 INCHES IN THE
LOWER ELEVATIONS ALONG AND WEST OF INTERSTATE 25 AND A DUSTING IN
PLACES FURTHER EAST. EXPECTED AMOUNTS WILL BE JUST BELOW ADVISORY
CRITERIA IN THE MOUNTAINS. AM CONCERNED THAT WITH THE STEEP LAPSE
RATES THE SNOWFALL RATES COULD AN INCH OR SO PER HOUR OVER MAINLY
THE MOUNTAINS FOR LATE THIS EVENING THROUGH THE REST OF TONIGHT.
MONDAY WILL BE CHILLY AND WINDY OVER MUCH OF THE AREA WITH SNOW
SHOWERS IN BANDS IN FAVORED MID LEVEL WIND CONVERGENT AREAS. AT
THIS TIME...HAVE KEPT WINDS JUST BELOW ADVISORY LEVELS IN THE
PANHANDLE FOR MONDAY BUT LATER SHIFTS WILL NEED TO MONITOR. THE
SHOWERS WILL DECREASE AND END AND CLOUDS DIMINISH MONDAY NIGHT AS
THE STORM SYSTEM MOVES FURTHER EAST AND ENDING THE CYCLONIC FLOW
ALOFT.
.LONG TERM...TUESDAY THROUGH SATURDAY...
LEANED TOWARDS THE GFS SERIES D+8-11 MEANS FOR THE LONG TERM
FORECAST...WHICH INDICATES DRY CONDITIONS FOR THE CWA THROUGH MUCH
OF THE WEEK. MODELS ALL SEEM TO DISAGREE WITH STRENGTH AND TIMING
OF THE UPPER TROUGH TOWARDS THE END OF THE PERIOD. NORTH TO NW FLOW
WILL BE OVER THE CWA AS AN UPPER RIDGE MOVES OVER THE WESTERN U.S.
SKIES WILL BE MOSTLY SUNNY OVER THE FORECAST AREA ON TUES WITH COOL
TEMPS. FOR WED...NW FLOW WILL CONT ALOFT AND TEMPERATURES WILL
BEGIN TO MODERATE. A WEAK SHORT WAVE WILL MOVE SE ACROSS THE
CENTRAL PLAINS ON THUR WHICH WILL INCREASE CLOUDS ACROSS THE EASTERN
HALF OF THE FORECAST AREA. SW FLOW WILL DEVELOP ALOFT FRI AS THE
UPPER RIDGE AXIS MOVES EAST OF THE AREA AND AN UPPER TROUGH
APPROACHES THE CWA. THANKSGIVING DAY AND FRIDAY LOOK LIKE THEY WILL
BE DRY AND VERY MILD. THE UPPER TROUGH WILL MOVE ACROSS THE
FORECAST AREA FRI NIGHT...BUT NOT MUCH MOISTURE SEEMS TO BE
ASSOCIATED WITH THIS SYSTEM. IN ADDITION...IT MOVES ACROSS THE CWA
QUICKLY AND WEAKENS. THE ASSOCIATED COLD FRONT WILL MOVE ACROSS THE
AREA FRI NIGHT OR SAT MORNING...RESULTING IN COLDER TEMPS FOR SAT.
JUST WENT WITH A SLIGHT CHANCE OF SNOW FOR THE MOUNTAINS WITH THIS
UPPER TROUGH. HIGH TEMPERATURES WILL BE AROUND NORMAL TUES AND
WED...10 TO 15 DEGREES ABOVE NORMAL FOR THANKSGIVING DAY AND
FRIDAY...AND AROUND NORMAL FOR SAT.
&&
.AVIATION...AREAS OF MVFR CEILINGS WILL PERSIST UNTIL MID MORNING
MAINLY IN SOUTHEAST WYOMING. OTHERWISE VFR CONDITIONS WILL BE OVER
THE CWA TODAY WITH WESTERLY SURFACE WINDS GUSTING AS HIGH AS 35
KNOTS OVER AND NEAR THE MOUNTAINS. CLOUD BASES WILL LOWER OVER THE
CWA TONIGHT WITH MVFR CEILINGS AND VISIBILITIES IN LIGHT SNOW
COMMON OVER THE SOUTH PART OF THE CWA FROM LATE EVENING THROUGH
SUNRISE MONDAY. THE SNOWY RANGE WILL BE OBSCURED TONIGHT AND FOR
MUCH OF MONDAY. A COLD FRONT WILL MOVE ACROSS THE CWA EARLY
TONIGHT WITH MORE NORTHERLY SURFACE WINDS GUSTING AS HIGH AS 35 KNOTS
AFTER ITS PASSAGE AND CONTINUING THROUGH MONDAY. ALONG WITH THE
WINDS ON MONDAY...AREAS OF MVFR CEILINGS AND VISIBILITIES IN SNOW
SHOWERS WILL OCCUR. WINDS WILL DECREASE MONDAY NIGHT. IN ADDITION
THE SNOW SHOWERS WILL END IN THE EVENING AND VFR CONDITIONS WILL
RETURN TO THE CWA BY LATE EVENING.
&&
.FIRE WEATHER...TEMPERATURES WILL BE NEAR NORMAL FOR TODAY AND THEN
COOLER ON MONDAY. LIGHT SNOW WILL BE OVER MUCH OF THE CWA TONIGHT
WITH SNOW SHOWERS ON MONDAY. THE RESULT WILL BE NO FIRE WEATHER
CONCERNS THROUGH MONDAY NIGHT. SURFACE WINDS WILL GUST AS HIGH AS
40 MPH OVER AND NEAR THE MOUNTAINS TODAY AND OVER AND EAST OF THE
LARAMIE RANGE LATER TONIGHT AND MONDAY.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&
$$
WEILAND/KMD
000
FXUS63 KUNR 221002
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
302 AM MST SUN NOV 22 2009
.DISCUSSION...09Z SURFACE ANALYSIS SHOWED COLD FRONT FROM EASTERN
ND INTO SOUTHWEST KS. WEAK RIDGE PUSHING INTO THE CWA. UPPER
TROUGH SLIPPING ACROSS EASTERN PORTIONS OF MT/WY/CO...WITH 90KT
JET STREAK CREATING SOME RETURNS ON KUDX WSR-88D. GIVEN SURFACE
T/TD SPREADS AND 00Z KUNR SOUNDING...LITTLE IF ANYTHING REACHING
GROUND. FOR TODAY...SHORTWAVE RIDGE MOVES OVER THE AREA AS
SURFACE RIDGE SLIPS EAST ALLOWING FOR RETURN FLOW IN THE WEST.
TONIGHT...SECONDARY UPPER TROUGH RACES INTO THE NORTHERN PLAINS
WITH MAIN JET STREAM STARTING TO FORM MAIN WAVE IN SOUTHERN WY/NE.
COULD BE LIGHT PRECIPITATION IN THE WEST.
MONDAY...MODEL CONSENSUS SHOWS UPPER LOW CLOSING OVER SOUTHERN NE.
THIS WILL BRING A CHANCE OF PRECIPITATION TO THE AREA AS IT MOVES
WEST TO EAST. BEST CHANCES WILL BE OVER SOUTH CENTRAL SD WITH BEST
LIFT/FRONTOGENESIS/UPPER LEVEL DIVERGENCE/MOISTURE COMBINE.
SURFACE LOW MOVES FROM THE BLACK HILLS TO IA/SD/NE BORDER.
GRADIENT WILL SUPPORT WINDY AREAS BEHIND THE LOW.
TUESDAY...UPPER RIDGE BUILDS OVER THE WEST AS YET ANOTHER WAVE
DROPS INTO THE UPPER MIDWEST. TAIL END OF WAVE/TROUGH WILL BRING
SMALL CHANCES FOR -SHSN TO THE AREA TUESDAY NIGHT.
EXTENDED...QUIET WEATHER WILL RETURN FOR THE MIDDLE INTO THE END
OF THE WORK WEEK AS AN UPPER LEVEL RIDGE BUILDS OVER THE AREA.
&&
.AVIATION...A FEW AREAS OF LIGHT SNOW MAY DEVELOP THIS EVENING
OVER NORTHEAST WYOMING AND FAR WESTERN SOUTH DAKOTA AS AN UPPER
LEVEL DISTURBANCE AND WEAK COLD FRONT PUSH INTO THE AREA. MOST
LOCATIONS WILL REMAIN VFR...THOUGH SOME LCL MVFR CIGS WILL BE
POSSIBLE TONIGHT OVER THE BLACK HILLS AND HIGHER TERRAIN OF NERN
WY.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&
$$
HELGESON/SCHILD
000
FXUS65 KCYS 220350
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
850 PM MST SAT NOV 21 2009
.UPDATE...MINOR GRIDDED FORECAST CHANGES FOR THE REST OF THE
NIGHT FOR SOME MODIFICATIONS TO TEMPERATURES...DEWPOINTS...
WINDS...CLOUD COVER AND SNOWFALL COVERAGE. RUBIN
&&
.PREV DISCUSSION... /ISSUED 346 PM MST SAT NOV 21 2009/
SHORT TERM...TONIGHT THROUGH MONDAY...UPPER TROUGH MOVING OUT OF
UT AND EASTERN ID CURRENTLY. MODELS SEEM TO BE HANDLING IT WELL
AND PROGRESS IT ACROSS WY TONIGHT TO NEAR EASTERN WY BORDER JUST
AFTER 12Z SUNDAY EXITING OUR EASTERN CWA BEFORE 18Z. PACIFIC COLD
FRONT HAS ADVANCED OUT OF SE WY NOW AND WILL PASS THROUGH NEBRASKA
PANHANDLE NEXT COUPLE HOURS. GUSTY WINDS THAT ACCOMPANIED THE
FRONT EARLIER HAVE DECREASED THROUGH AFTERNOON. THERE WILL BE LOTS
OF CLOUDS OVER THE CWA TONIGHT WITH SOME SNOW SHOWERS OVER THE
MOUNTAINS ACCUMULATING TO PERHAPS AN INCH OR SO. A FEW SNOW
SHOWERS ARE ALSO POSSIBLE KLAR-KCYS PER GFS SO INCLUDED A LOW POP
THERE AS WELL TONIGHT. IMPROVEMENT FROM WEST TO EAST BEHIND UPPER
TROUGH LATE TONIGHT THEN SHORTWAVE RIDGE WILL PREVAIL OVER THE CWA
SUNDAY BRINGING DRY CONDITIONS. NEXT UPPER TROUGH IN THE
PROGRESSIVE UPPER AIR PATTERN WILL MOVE IN SUNDAY NIGHT... WITH A
TIMING NOT ALL THAT UNLIKE THE ONE TONIGHT. DIFFERENCE IS THE
LATTER UPPER TROUGH IS MUCH STRONGER WITH VEERING UPPER FLOW AND
AN UPPER LOW DEVELOPS WITH IT TO OUR EAST. IT ALSO IS SLOWER TO
MOVE OUT. MODELS ARE GETTING CLOSER TO A CONVERGENT SOLUTION ON
THIS LATTER TROUGH BUT STILL SHOW SOME DIFFERENCES...UPPER LOW
DOES NOT REALLY GET CRANKED UP UNTIL IT GETS TOO FAR EAST OF US.
GFS HAS SLOWED DOWN AND ECMWF IS NOT QUITE AS DEEP AS FAST AS IT
WAS ON THE 12Z FRIDAY RUN. STILL...THERE WILL BE WIND AND SNOW FOR
MOST AREAS WITH THIS FEATURE AND ITS ASSOCIATED COLD FRONT...WITH
A FEW INCHES FALLING IN THE MOUNTAINS. AN ADVISORY MAY END UP
BEING NECESSARY FOR THE SOUTH CENTRAL WY MOUNTAINS SUNDAY NIGHT
AND MONDAY MORNING WHILE A WIND ADVISORY IS LIKELY FOR THE
NEBRASKA PANHANDLE MONDAY. BOTH ARE TOO EARLY FOR NOW. TEMPS WILL
BE COLDER BOTH DAYS.
LONG TERM...MONDAY NIGHT THROUGH SATURDAY...MODELS IN GOOD
AGREEMENT EARLIER IN THE WEEK...AND THEN SHOW DIVERGING SOLUTIONS
LATE IN THE WEEK AND EARLY NEXT WEEK. GFS...GEM...AND ECMWF SHOW
MAINLY NORTHERLY FLOW ACROSS THE FRONT RANGE THROUGH THURSDAY AS AN
UPPER LEVEL TROUGH EXITS EAST OF THE REGION ON TUESDAY...AND A
BACKDOOR POLAR FRONT MOVES INTO THE HIGH PLAINS ON WEDNESDAY. THIS
WILL KEEP TEMPS ON THE COLD SIDE THROUGH THE MIDDLE OF NEXT WEEK
WITH MODELS HINTING AT HIGHS IN THE 30S ACROSS MOST OF THE AREA AND
LOWS IN THE TEENS AND TWENTIES. DID NOT GO QUITE THAT LOW IN THE
FORECAST WITH THE ECMWF SHOWING THE BULK OF THE COLDER AIR FURTHER
TO THE EAST. DO NOT EXPECT MUCH PRECIP AS THE MAIN JET ENERGY WILL
BE EAST OF THE AREA AND MODELS SHOW LITTLE MOISTURE WITH THE FRONT.
KEPT LOW POP ACROSS THE AREA THROUGH THE WEEK WITH 20 PCT POP ACROSS
THE NRN RIDGES OF THE NEBRASKA PANHANDLE AND ERN WYOMING. BY LATE IN
THE WEEK...00Z GFS AND GFS ENSEMBLE SHOW AN UPPER LEVEL RIDGE
DRIFTING EAST OVER THE AREA RESULTING IN WARMER TEMPS AND CLEARING
SKIES. IN CONTRAST...THE ECMWF SHOWS AN UPPER LEVEL TROUGH FROM THE
NRN PACIFIC PUSHING ACROSS THE NORTHWEST COAST ON FRIDAY AND INTO
THE ROCKY MOUNTAIN REGION FOR NEXT SATURDAY...WITH SOME SNOW OVER
THE AREA AND A CONTINUATION OF COLD TEMPS. WITH POOR MODEL
AGREEMENT...LIMITED CONFIDENCE IN THE FORECAST AFTER THANKSGIVING
DAY. INCREASED POP TOWARDS CLIMO FOR FRIDAY NIGHT AND NEXT SATURDAY
AND KEPT TEMPS NEAR OR SLIGHTLY BELOW NORMAL NORMAL.
AVIATION...MAINLY VFR CONDITIONS EXPECTED THROUGH TONIGHT WITH
WESTERLY WINDS BETWEEN 15 TO 25 KTS AND GUSTS UP TO 35 KTS EARLY
THIS EVENING...DIMINISHING TO 10 TO 15 KTS AFTER SUNSET. THERE IS A
10 PCT CHANCE OF MVFR CONDITIONS AND BRIEF LIGHT SNOW THIS EVENING AT
KRWL...KCYS AND KLAR AS A WEAK COLD FRONT PUSHES ACROSS THE AREA
TONIGHT...OTHERWISE...EXPECT CIGS TO REMAIN ABOVE 3K FEET AGL
TONIGHT THROUGH TOMORROW WITH ANY SNOW MAINLY CONFINED TO THE
MOUNTAINS.
FIRE WEATHER...NO CONCERNS THROUGH MONDAY.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&
$$
SHORT TERM/FIRE WEATHER...JLH
LONG TERM/AVIATION...TJT
000
FXUS63 KUNR 212251
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
248 PM MST SAT NOV 21 2009
.DISCUSSION...21Z SFC ANALYSIS SHOWS LOW PRESSURE CENTERED OVER THE
SASKATCHEWAN/MANITOBA BORDER WITH A LEADING N/S ORIENTED TROUGH
ACROSS THE CENTRAL DAKOTAS...AND A TRAILING COLD FRONT CURRENTLY
CROSSING WESTERN SOUTH DAKOTA.
FOR TONIGHT...WINDS WILL DIMINISH EARLY THIS EVENING AS A WEAK SFC
HIGH SLIDES INTO THE AREA. TEMPERATURES WILL FALL TO NEAR NORMAL.
ON SUNDAY...A WEAK SHORTWAVE RIDGE WILL QUICKLY CROSS THE AREA IN
ADVANCE OF A FAST MOVING SHORTWAVE ON SUNDAY NIGHT. THE SURFACE HIGH
WILL QUICKLY SHIFT SOUTH WITH SOUTHERLY RETURN FLOW DEVELOPING OVER
WESTERN PORTIONS OF THE CWA. THERE WILL BE ENOUGH FORCING/MOISTURE
PRESENT TO INCLUDE LOW POPS ON SUNDAY NIGHT. TEMPERATURES WILL
CONTINUE NEAR GUIDANCE.
ON MONDAY...SOME DIFFERENCES REMAIN IN MODEL HANDLING OF SHORTWAVE
TROUGH. 00Z NAM/ECMWF/GEM CONTINUE TO TREND SOUTH AND EAST...WITH
THE GFS CONTINUING TO INDICATE A MORE NORTHERLY TRACK. WILL GO WITH
MODEL TRENDS AT THIS POINT...WHICH WILL KEEP BEST PRECIPITATION AWAY
FROM THE CWA...BUT WILL STILL INCLUDE A CHANCE OF SNOW OR RAIN WITH
THE BEST CHANCE OF PRECIPITATION OVER OUR SOUTH CENTRAL SOUTH DAKOTA
ZONES.
EXTENDED...UPPER LOW IS EXPECTED TO BE LOCATED OVER EASTERN NEBRASKA
INTO WESTERN IOWA ON TUESDAY...BRINGING A CHANCE OF RAIN AND SNOW TO
PORTIONS OF SOUTH CENTRAL SOUTH DAKOTA. SEVERAL GFS ENSEMBLE MEMBERS
INDICATING AN UPPER LOW DEVELOPING ACROSS THIS AREA. GEM AND ECMWF
ALSO LEANING TOWARD THIS SOLUTION. SYSTEM WILL EXIT THE AREA
TUESDAY AFTERNOON. SHORTWAVE WILL SWEEP ACROSS THE CWA EARLY
WEDNESDAY MORNING. ATTM IT APPEARS CWA WILL REMAIN DRY THROUGH
MIDWEEK. EXPECT RIDGE TO BUILD ACROSS THE WESTERN CONUS LATE NEXT
WEEK. RMOP INDICATES HIGH PREDICTABILITY WITH THIS SCENARIO...SO
WILL KEEP FORECAST DRY THROUGH LATE NEXT WEEK.
&&
.AVIATION...VFR CONDITIONS CAN BE EXPECTED THROUGH THE FORECAST
PERIOD.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&
$$
000
FXUS65 KCYS 212246
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
346 PM MST SAT NOV 21 2009
.SHORT TERM...TONIGHT THROUGH MONDAY...UPPER TROUGH MOVING OUT OF
UT AND EASTERN ID CURRENTLY. MODELS SEEM TO BE HANDLING IT WELL
AND PROGRESS IT ACROSS WY TONIGHT TO NEAR EASTERN WY BORDER JUST
AFTER 12Z SUNDAY EXITING OUR EASTERN CWA BEFORE 18Z. PACIFIC COLD
FRONT HAS ADVANCED OUT OF SE WY NOW AND WILL PASS THROUGH NEBRASKA
PANHANDLE NEXT COUPLE HOURS. GUSTY WINDS THAT ACCOMPANIED THE
FRONT EARLIER HAVE DECREASED THROUGH AFTERNOON. THERE WILL BE LOTS
OF CLOUDS OVER THE CWA TONIGHT WITH SOME SNOW SHOWERS OVER THE
MOUNTAINS ACCUMULATING TO PERHAPS AN INCH OR SO. A FEW SNOW
SHOWERS ARE ALSO POSSIBLE KLAR-KCYS PER GFS SO INCLUDED A LOW POP
THERE AS WELL TONIGHT. IMPROVEMENT FROM WEST TO EAST BEHIND UPPER
TROUGH LATE TONIGHT THEN SHORTWAVE RIDGE WILL PREVAIL OVER THE CWA
SUNDAY BRINGING DRY CONDITIONS. NEXT UPPER TROUGH IN THE
PROGRESSIVE UPPER AIR PATTERN WILL MOVE IN SUNDAY NIGHT... WITH A
TIMING NOT ALL THAT UNLIKE THE ONE TONIGHT. DIFFERENCE IS THE
LATTER UPPER TROUGH IS MUCH STRONGER WITH VEERING UPPER FLOW AND
AN UPPER LOW DEVELOPS WITH IT TO OUR EAST. IT ALSO IS SLOWER TO
MOVE OUT. MODELS ARE GETTING CLOSER TO A CONVERGENT SOLUTION ON
THIS LATTER TROUGH BUT STILL SHOW SOME DIFFERENCES...UPPER LOW
DOES NOT REALLY GET CRANKED UP UNTIL IT GETS TOO FAR EAST OF US.
GFS HAS SLOWED DOWN AND ECMWF IS NOT QUITE AS DEEP AS FAST AS IT
WAS ON THE 12Z FRIDAY RUN. STILL...THERE WILL BE WIND AND SNOW FOR
MOST AREAS WITH THIS FEATURE AND ITS ASSOCIATED COLD FRONT...WITH
A FEW INCHES FALLING IN THE MOUNTAINS. AN ADVISORY MAY END UP
BEING NECESSARY FOR THE SOUTH CENTRAL WY MOUNTAINS SUNDAY NIGHT
AND MONDAY MORNING WHILE A WIND ADVISORY IS LIKELY FOR THE
NEBRASKA PANHANDLE MONDAY. BOTH ARE TOO EARLY FOR NOW. TEMPS WILL
BE COLDER BOTH DAYS.
.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...MODELS IN GOOD
AGREEMENT EARLIER IN THE WEEK...AND THEN SHOW DIVERGING SOLUTIONS
LATE IN THE WEEK AND EARLY NEXT WEEK. GFS...GEM...AND ECMWF SHOW
MAINLY NORTHERLY FLOW ACROSS THE FRONT RANGE THROUGH THURSDAY AS AN
UPPER LEVEL TROUGH EXITS EAST OF THE REGION ON TUESDAY...AND A
BACKDOOR POLAR FRONT MOVES INTO THE HIGH PLAINS ON WEDNESDAY. THIS
WILL KEEP TEMPS ON THE COLD SIDE THROUGH THE MIDDLE OF NEXT WEEK
WITH MODELS HINTING AT HIGHS IN THE 30S ACROSS MOST OF THE AREA AND
LOWS IN THE TEENS AND TWENTIES. DID NOT GO QUITE THAT LOW IN THE
FORECAST WITH THE ECMWF SHOWING THE BULK OF THE COLDER AIR FURTHER
TO THE EAST. DO NOT EXPECT MUCH PRECIP AS THE MAIN JET ENERGY WILL
BE EAST OF THE AREA AND MODELS SHOW LITTLE MOISTURE WITH THE FRONT.
KEPT LOW POP ACROSS THE AREA THROUGH THE WEEK WITH 20 PCT POP ACROSS
THE NRN RIDGES OF THE NEBRASKA PANHANDLE AND ERN WYOMING. BY LATE IN
THE WEEK...00Z GFS AND GFS ENSEMBLE SHOW AN UPPER LEVEL RIDGE
DRIFTING EAST OVER THE AREA RESULTING IN WARMER TEMPS AND CLEARING
SKIES. IN CONTRAST...THE ECMWF SHOWS AN UPPER LEVEL TROUGH FROM THE
NRN PACIFIC PUSHING ACROSS THE NORTHWEST COAST ON FRIDAY AND INTO
THE ROCKY MOUNTAIN REGION FOR NEXT SATURDAY...WITH SOME SNOW OVER
THE AREA AND A CONTINUATION OF COLD TEMPS. WITH POOR MODEL
AGREEMENT...LIMITED CONFIDENCE IN THE FORECAST AFTER THANKSGIVING
DAY. INCREASED POP TOWARDS CLIMO FOR FRIDAY NIGHT AND NEXT SATURDAY
AND KEPT TEMPS NEAR OR SLIGHTLY BELOW NORMAL NORMAL.
&&
.AVIATION...MAINLY VFR CONDITIONS EXPECTED THROUGH TONIGHT WITH
WESTERLY WINDS BETWEEN 15 TO 25 KTS AND GUSTS UP TO 35 KTS EARLY
THIS EVENING...DIMINISHING TO 10 TO 15 KTS AFTER SUNSET. THERE IS A
10 PCT CHANCE OF MVFR CONDITIONS AND BRIEF LIGHT SNOW THIS EVENING AT
KRWL...KCYS AND KLAR AS A WEAK COLD FRONT PUSHES ACROSS THE AREA
TONIGHT...OTHERWISE...EXPECT CIGS TO REMAIN ABOVE 3K FEET AGL
TONIGHT THROUGH TOMORROW WITH ANY SNOW MAINLY CONFINED TO THE
MOUNTAINS.
&&
.FIRE WEATHER...NO CONCERNS THROUGH MONDAY.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&
$$
SHORT TERM...JLH
LONG TERM...TJT
AVIATION...TJT
000
FXUS65 KRIW 212214
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
314 PM MST SAT NOV 21 2009
.SHORT TERM...TONIGHT THROUGH TUESDAY
FIRST WAVE OF THE SPLIT TROUGH MOVED THROUGH BY MID MORNING WITH AN
INCH OR TWO OF SNOWFALL OVER THE FAR WEST MOUNTAINS AND VALLEYS.
SECOND SHORTWAVE MOVING ACROSS LATE THIS MORNING AND MID AFTERNOON
WITH SOME LIGHT SNOW FALLING MAINLY IN THE WESTERN MOUNTAINS. THE
SNOW WILL BE ENDING HERE IN THE EARLY TO MID EVENING HOURS AS THE
WAVE MOVES THROUGH AND SHORTWAVE RIDGE BUILDS IN. HAD SOME
BORDERLINE HIGH WINDS AROUND CASPER AND SOUTHEAST FREMONT COUNTY.
WINDS ARE STILL QUITE WINDY OVER NATRONA AND SOUTHEAST FREMONT. THE
WINDS WILL TAPER SOME IN THE EVENING AND IN THE OVERNIGHT HOURS
BEFORE PICKING BACK UP AGAIN AS THE NEXT SYSTEM APPROACHES. THIS
NEXT SYSTEM CURRENTLY MOVING QUICKLY TOWARDS THE PAC NW. THIS
SYSTEM WILL MOVE ON SHORE AFTER MIDNIGHT AND BEGIN TO SPREAD
MOISTURE INTO THE WEST SHORTLY BEFORE NOON. THIS AS THE NOSE OF
CYCLONICALLY CURVED JET MOVES ACROSS SOUTHERN IDAHO AND INTO WESTERN
WYOMING. THE JET DIGS SOUTHEAST INTO SW WY AND INTO NE UT AND NW CO
IN THE AFTERNOON AND EVENING. COLD FRONT MOVES THROUGH IN THE LATE
AFTERNOON AND EARLY EVENING...WITH THE SNOWFALL WINDING DOWN TO
MAINLY THE MOUNTAINS. THIS WILL BRING A 6 TO 9 HOUR PERIOD OF
SNOWFALL OF PERHAPS 0.5 INCH PER HOUR SNOWFALL RATES IN THE WESTERN
MOUNTAINS. LIGHT SNOW SHOWERS WILL LIKELY PERSIST IN THE WESTERN
MOUNTAINS...POSSIBLY IN THE VALLEYS. MEANWHILE NORTHWEST WINDS WILL
INCREASE IN THE EVENING OVER AREAS EAST OF THE DIVIDE...AND EVEN THE
UPPER GREEN BASIN. H7 WAVE MOVES THROUGH NORTH CENTRAL WYOMING
SUNDAY NIGHT AS WELL...BRINGING A DECENT CHANCE OF SNOW TO THE NORTH
AND EASTERN BIGHORNS AND TO JOHNSON COUNTY. THE NORTHWEST FLOW
CONTINUES OVER THE CWA MONDAY...WITH SOME LINGERING SNOW SHOWERS.
THINGS STABILIZE AND DRY OUT IN THE AFTERNOON. NORTHWEST WINDS TO
PERSIST MONDAY AS WELL THEN TAPERING IN THE EVENING AS THE TROUGH
DEPARTS. LARGE RIDGE BUILDS IN OVER THE GREAT BASIN TUESDAY WITH A
CLIPPER MOVING SOUTHEAST FROM THE ALBERTA/SASKATCHEWAN REGION OF
CANADA. SOME LIGHT SNOW WILL APPROACH FAR NORTHERN WYOMING. AS A
STRONG JET ON THE BASE OF THE CLIPPER DIGS INTO CENTRAL MONTANA. H7
TEMPERATURES OF -15C MOVES INTO THE WEST TONIGHT AND -10C OR SO OVER
THE CENTRAL. WITH CLEAR PATCHES OVERNIGHT THE FAR WEST VALLEYS SUCH
AS THE UPPER GREEN COULD DROP INTO THE SINGLE DIGITS AND CLOSE TO
ZERO. EXPECT THESE NEAR ZERO TEMPERATURES TO BE MORE LIKELY SUNDAY
NIGHT WITH EVEN SOME SUB ZERO TEMPERATURES.
.LONG TERM...TUESDAY NIGHT THROUGH SATURDAY
DRY CONDITIONS WITH A WARMING TREND ARE EXPECTED TUESDAY NIGHT THROUGH
THANKSGIVING DAY. THE NEXT PACIFIC STORM SYSTEM WILL BRING A
CHANCE OF SNOW TO THE WEST FRIDAY AND COOLER CONDITIONS WITH
CHANCES OF SNOW ACROSS CENTRAL WYOMING FRIDAY NIGHT AND SATURDAY.
LATEST ECMWF SHOWING A SOLUTION SIMILAR TO LAST FEW GEM RUNS WITH A
CLIPPER DIVING DOWN FRONT SIDE OF INTERMOUNTAIN WEST UPPER RIDGE
INTO BACKSIDE OF UPPER LOW OVER UPPER MISSISSIPPI VALLEY TUESDAY AND
TUESDAY NIGHT...KEEPING SYSTEM WELL NORTH AND EAST OF WYOMING.
GFS...SHOWING A STRONGER CLIPPER DIVING INTO THE NORTHERN
PLAINS...IS ALSO TRENDING IN THIS DIRECTION. FORECAST SIDES WITH
ECMWF AND GEM RESULTING IN A DRY FORECAST TUESDAY WITH HIGH
TEMPERATURES AROUND 10F WARMER THAN MONDAY...OR UPPER 30S TO NEAR 50
MOST BASINS AND VALLEYS. UPPER RIDGE EXPANDS ACROSS AREA WEDNESDAY
AND THANKSGIVING DAY WITH DRY AND UNSEASONABLY MILD HIGH
TEMPERATURES THOUGH VALLEY INVERSIONS WILL CONTINUE TO KEEP
TEMPERATURES 10F-15F BELOW FULL MIXING POTENTIAL AS HAS BEEN THE
CASE WITH THE LAST FEW DAYS OF CLEAR SKIES/LIGHT WIND. NIGHTTIME
LOWS WILL BE MORE NEAR NORMAL WITH GOOD RADIATIONAL COOLING. MODEL
SPREAD INCREASES FRIDAY AND SATURDAY WITH GFS CONTINUING TO HANDLE
SPLIT FLOW OF LAST FEW WEEKS POORLY...TOO FAR NORTH AND TOO
PROGRESSIVE WITH INCOMING PACIFIC ENERGY. ECMWF SPLITS NEXT PACIFIC
SYSTEM ALONG WEST COAST FRIDAY MORNING WITH MOST OF THIS ENERGY
DIVING INTO THE GREAT BASIN FRIDAY NIGHT. ECMWF IS LIKELY NOT
PROGRESSIVE ENOUGH...HOLDING A CLOSED LOW BACK OVER AZ/NM INTO
SUNDAY. FORECAST BRINGS IN CHANCES OF PRECIPITATION INTO THE WEST
FRIDAY...SPREADING EAST OF THE DIVIDE FRIDAY NIGHT AND SATURDAY
ALONG WITH COOLER TEMPERATURES MORE NEAR SEASONAL NORMALS.
&&
.AVIATION...
VFR TO MVFR CONDITIONS ARE EXPECTED WEST OF THE DIVIDE WITH ISOLATED
SNOW SHOWERS CONTINUING THROUGH APPROXIMATELY 06Z SUN. EXPECT MAINLY
LOCAL MOUNTAIN TOP OBSCURATION THROUGH THIS SAME TIME. EAST OF THE
CONTINENTAL DIVIDE...VFR CONDITIONS CONTINUE THROUGH 18Z SUNDAY.
LOCALLY STRONG SOUTHWEST WIND FROM 20 TO 30KTS WITH GUSTS TO 50KTS
IS POSSIBLE BTWN 09Z-14Z SUNDAY VCNTY OF KCOD.
&&
.FIRE WEATHER...
ANOTHER TROUGH WILL APPROACH FOR SUNDAY BRINGING ANOTHER ROUND OF
SNOW IN THE WEST IN THE AFTERNOON AND EVENING. WINDS WILL ALSO BE
ON THE INCREASE WITH AREAS OF STRONG WINDS IN THE TYPICAL SPOTS.
NORTHWEST WINDS WILL INCREASE IN THE EVENING EAST OF THE DIVIDE AND
THE UPPER GREEN BASIN SUNDAY EVENING AND PERSIST THROUGH MONDAY.
LIGHT SNOW SHOWERS WILL DISSIPATE MONDAY AS HIGH PRESSURE BUILDS
IN. ANOTHER SYSTEM COULD CLIP THE NORTHEAST TUESDAY NIGHT WITH SOME
LIGHT SNOW. OTHERWISE DRY AND MILDER CONDITIONS EXPECTED THROUGH THE
UPCOMING WEEK.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...TWB
LONG TERM...AEM
AVIATION...CHURCH
FIRE WEATHER...TWB
000
FXUS63 KUNR 212148
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
248 PM MST SAT NOV 21 2009
.DISCUSSION...21Z SFC ANALYSIS SHOWS LOW PRESSURE CENTERED OVER THE
SASKATCHEWAN/MANITOBA BORDER WITH A LEADING N/S ORIENTED TROUGH
ACROSS THE CENTRAL DAKOTAS...AND A TRAILING COLD FRONT CURRENTLY
CROSSING WESTERN SOUTH DAKOTA.
FOR TONIGHT...WINDS WILL DIMINISH EARLY THIS EVENING AS A WEAK SFC
HIGH SLIDES INTO THE AREA. TEMPERATURES WILL FALL TO NEAR NORMAL.
ON SUNDAY...A WEAK SHORTWAVE RIDGE WILL QUICKLY CROSS THE AREA IN
ADVANCE OF A FAST MOVING SHORTWAVE ON SUNDAY NIGHT. THE SURFACE HIGH
WILL QUICKLY SHIFT SOUTH WITH SOUTHERLY RETURN FLOW DEVELOPING OVER
WESTERN PORTIONS OF THE CWA. THERE WILL BE ENOUGH FORCING/MOISTURE
PRESENT TO INCLUDE LOW POPS ON SUNDAY NIGHT. TEMPERATURES WILL
CONTINUE NEAR GUIDANCE.
ON MONDAY...SOME DIFFERENCES REMAIN IN MODEL HANDLING OF SHORTWAVE
TROUGH. 00Z NAM/ECMWF/GEM CONTINUE TO TREND SOUTH AND EAST...WITH
THE GFS CONTINUING TO INDICATE A MORE NORTHERLY TRACK. WILL GO WITH
MODEL TRENDS AT THIS POINT...WHICH WILL KEEP BEST PRECIPITATION AWAY
FROM THE CWA...BUT WILL STILL INCLUDE A CHANCE OF SNOW OR RAIN WITH
THE BEST CHANCE OF PRECIPITATION OVER OUR SOUTH CENTRAL SOUTH DAKOTA
ZONES.
EXTENDED...UPPER LOW IS EXPECTED TO BE LOCATED OVER EASTERN NEBRASKA
INTO WESTERN IOWA ON TUESDAY...BRINGING A CHANCE OF RAN AND SNOW TO
PORTIONS OF SOUTH CENTRAL SOUTH DAKOTA. SEVERAL GFS ENSEMBLE MEMBERS
INDICATING AN UPPER LOW DEVELOPING ACROSS THIS AREA. GEM AND ECMWF
ALSO LEANING TOWARD THIS SOLUTION. SYSTEM WILL EXIT THE AREA
TUESDAY AFTERNOON. SHORTWAVE WILL SWEEP ACROSS THE CWA EARLY
WEDNESDAY MORNING. ATTM IT APPEARS CWA WILL REMAIN DRY THROUGH
MIDWEEK. EXPECT RIDGE TO BUILD ACROSS THE WESTERN CONUS LATE NEXT
WEEK. RMOP INDICATES HIGH PREDICTABILITY WITH THIS SCENARIO...SO
WILL KEEP FORECAST DRY THROUGH LATE NEXT WEEK.
&&
.AVIATION...VFR CONDITIONS CAN BE EXPECTED THROUGH THE FORECAST
PERIOD.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&
$$
000
FXUS65 KCYS 211905
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1205 PM MST SAT NOV 21 2009
.UPDATE...HAVE ALLOWED HI WIND WARNING FOR KARL TO EXPIRE AT 19Z AS
WINDS THERE HAVE DECREASED QUITE A BIT SINCE 1815Z. JLH
&&
.PREV DISCUSSION... /ISSUED 926 AM MST SAT NOV 21 2009/
UPDATE...HAVE ISSUED LOCAL HIGH WIND WARNING FOR ARLINGTON AREA OF
SOUTH CENTRAL WY UNTIL 19Z. SUSTAINED SPEEDS OF 40 MPH HAVE BEEN
OCCURRING THERE SINCE 1430Z WITH ONE GUST TO 60 MPH AROUND THEN AND
MORE TO 65 MPH CURRENTLY. WINDS SHOULD SLOWLY DECREASE BEHIND A
COLD FRONT BY MID AFTERNOON. JLH
PREV DISCUSSION... /ISSUED 300 AM MST SAT NOV 21 2009/
SHORT TERM...TODAY THROUGH SUNDAY NIGHT
AN ACTIVE PERIOD WILL BE IN STORE FOR THE CWA THROUGH 12Z MONDAY.
A SHORTWAVE TROUGH CURRENTLY OVER THE PACIFIC NORTHWEST WILL MOVE
EAST AND ACROSS THE CWA THROUGH 18Z SUNDAY. MODELS HAVE BEEN
TRENDING A BIT SLOWER WITH THE FEATURE THE PAST FEW RUNS BUT ARE
NOW FAIRLY CLOSE WITH THE AXIS OVER FAR EASTERN WYOMING AT 12Z
SUNDAY. THE ASSOCIATED PACIFIC COLD FRONT WAS LOCATED FROM
WESTERN MONTANA TO IDAHO EARLY THIS MORNING WITH 2 TO 3 MB THREE
HOURLY SURFACE PRESSURE RISES BEHIND THE FRONT. THE FRONT WILL
MOVE ACROSS THIS AFTERNOON AND EARLY EVENING. CONSIDERABLE MID
AND HIGH CLOUDS WILL BE OVER THE CWA TODAY AND TONIGHT PRIOR TO
THE PASSAGE OF THE SHORTWAVE TROUGH. IT WILL ALSO BE WINDY OVER
AND NEAR THE MOUNTAINS TODAY WITH THE SURFACE LOW PRESSURE TROUGH
OVER FAR EASTERN WYOMING. WIND GUSTS SINCE 06Z HAVE BEEN AS HIGH
AS 52 MPH AT KCPR...KARL AND KRWL. THE WIND SPEEDS MAY BE THE
HIGHEST THROUGH THE MORNING WITH THE TEMPERATURE INVERSION
PRESENT AND BASED AROUND 750 MB. TEMPERATURES ARE CURRENTLY FAIRLY
MILD IN MANY LOCATIONS AND WILL HELP TO PRODUCE ANOTHER DAY WITH
ABOVE NORMAL TEMPERATURES OVER THE EASTERN PART OF THE CWA AHEAD
OF THE FRONT. THERE IS CURRENTLY BANDS OF PRECIPITATION ON THE
KMTX AND KSFX RADARS ASSOCIATED WITH THE BAROCLINIC CLOUD BAND NOW
OVER EASTERN IDAHO AND NORTHERN UTAH. THE MAIN THREAT OF LIGHT
SNOW WILL BE OVER AND NEAR THE SNOWY RANGE TONIGHT WITH THE
PASSAGE OF THE SHORTWAVE TROUGH. OTHERWISE EXPECT MOST OF THE CWA
TO REMAIN DRY. MODELS DIFFER ON THE TIMING AND AMPLITUDE OF THE
NEXT SHORTWAVE TROUGH. THE FEATURE WILL DEEPEN OVER THE ROCKIES
SUNDAY NIGHT WITH THE ASSOCIATED SURFACE COLD FRONT MOVING ACROSS
THE CWA SUNDAY NIGHT. THE 00Z ECMWF CONTINUES TO BE SLOWER THAN
MOST OF THE OTHER MODELS WITH THE SHORTWAVE TROUGH BUT HAS TRENDED
FASTER AND WITH LESS AMPLITUDE THAN ITS 12Z RUN. THE 00Z ECMWF IS
FAVORED BY HPC AND SO WILL USE THAT MODEL AGAIN FOR THIS
FORECAST... ESPECIALLY SUNDAY NIGHT. THE LEFT EXIT REGION OF THE
300 MB JET WILL AFFECT MAINLY THE SOUTH PART OF THE CWA SUNDAY
NIGHT AND MOISTURE WILL INCREASE. FOR NOW WILL CONTINUE THE TREND
OF INCREASING POPS AND SNOW AMOUNTS OVER THE CWA FOR SUNDAY NIGHT.
TWO TO FIVE INCHES OF NEW SNOW ARE POSSIBLE IN THE SNOWY RANGE
SUNDAY NIGHT...WITH AN INCH OR LESS OVER MOST OF THE REST OF THE
SOUTH PART OF THE CWA.
LONG TERM...MONDAY THROUGH FRIDAY
LEANED TOWARDS THE 00Z ECMWF AS IT SEEMS TO BE HANDLING THE SPLIT
FLOW BETTER THAN THE GFS...GEMS OR UKMET. THE UPPER TROUGH WILL
MOVE ACROSS THE CWA ON MON...WITH THE AXIS MOVING EAST OF THE
FORECAST AREA BY EVENING. AN UPPER LOW WILL FORM OVER THE CENTRAL
PLAINS MON NIGHT. COLD TEMPERATURES CAN BE EXPECTED ACROSS THE AREA
MON WITH BRISK WINDS IN THE MORNING. SOME LIGHT SNOW WILL FALL
ACROSS THE AREA...WITH THE BEST CHANCES IN THE MOUNTAINS...BUT
LOWERED POPS DUE TO BEST DYNAMICS SHIFTING EAST AS THE TROUGH AXIS
MOVES FAIRLY QUICK ACROSS THE CWA DURING THE DAY. AN INCH OR TWO
ADDITIONAL SNOW WILL FALL IN THE MOUNTAINS...WITH LESS THAN AN INCH
AT THE LOWER ELEVATIONS. ON TUES...NW FLOW WILL SET UP ALOFT AS AN
UPPER RIDGE BUILD OVER THE WESTERN U.S. DRY CONDITIONS WILL PERSIST
FROM TUES THROUGH FRIDAY. TEMPERATURES WILL MODERATE A FEW DEGREES
ON TUESDAY UNDER PARTLY CLOUDY SKIES. FOR WED...MILD CONDITIONS
WILL OCCUR AND THEN VERY MILD FOR THUR AND FRI WITH DOWNSLOPE WINDS
AND SUNNY SKIES. THE NW UPPER FLOW WILL FLATTEN OUT FRI AS AN UPPER
TROUGH MOVES INLAND FROM THE WEST COAST. A COLD FRONT WILL MOVE
ACROSS THE CWA LATE FRI NIGHT/EARLY SAT MORNING. HIGH TEMPERATURES
WILL BE FROM 5 TO 8 DEGREES BELOW NORMAL MON...AROUND NORMAL TUES
AND WED...AND 5 TO 8 DEGREES ABOVE NORMAL FOR THANKSGIVING DAY AND
THE FRIDAY HOLIDAY SHOPPING DAY.
AVIATION...
VFR CONDITIONS WILL CONTINUE OVER THE CWA TODAY. CLOUD BASES WILL
LOWER TONIGHT BUT SHOULD STILL REMAIN VFR. THE SNOWY RANGE WILL BE
OBSCURED TONIGHT. WEST WINDS WILL GUST AS HIGH AS 50 MPH THROUGH
MID MORNING OVER AND NEAR THE MOUNTAINS. THOSE WINDS WILL PRODUCE
TURBULENT CONDITIONS AT AIRPORTS SUCH AS KRWL...KLAR...KDGW...KEAN
AND KCYS. CLOUDS WILL ONCE AGAIN LOWER SUNDAY NIGHT OVER THE CWA
WITH AT LEAST PERIODS OF MVFR CEILINGS AND VISIBILITIES IN SNOW
OVER THE SOUTH PART OF THE CWA. THE SNOWY RANGE WILL BE OBSCURED
AGAIN SUNDAY NIGHT. ICING WILL BE A CONCERN WITH COOLER
TEMPERATURES AND INCREASED MOISTURE.
FIRE WEATHER...
WESTERLY SURFACE WINDS WILL GUST AS HIGH AS 50 MPH OVER AND NEAR THE
MOUNTAINS THROUGH MID MORNING. LOWER WIND SPEEDS ARE THEN EXPECTED
THROUGH SUNDAY. MINIMUM RELATIVE HUMIDITIES WILL BE BETWEEN 23
AND 30 PERCENT THIS AFTERNOON AND AGAIN SUNDAY AFTERNOON. EVEN
WITH THE GUSTY WINDS...FIRE WEATHER CONCERNS WILL BE MINIMAL FOR
THIS WEEKEND.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&
$$
SHORT TERM/AVIATION...WEILAND
LONG TERM...KMD
000
FXUS63 KUNR 211746
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1046 AM MST SAT NOV 21 2009
.DISCUSSION...17Z SFC ANALYSIS SHOWS LOW PRESSURE OVER CENTRAL
SASKATCHEWAN WITH A LEADING TROUGH EXTENDING ACROSS WESTERN NORTH
DAKOTA AND CENTRAL SOUTH DAKOTA...WITH A COOL FRONT EXTENDING FROM
WESTERN NORTH DAKOTA TO NEAR KGCC IN NORTHEASTERN WYOMING. A BAND
OF CIRRUS WAS LOCATED OVER WESTERN SOUTH DAKOTA MOVING SLOWLY
EAST. THE TIGHT PRESSURE GRADIENT ASSOCIATED WITH THE TROUGH AND
FRONT HAS CREATED WINDY CONDITIONS ACROSS MUCH OF THE FORECAST
AREA THIS MORNING. HAVE UPDATED FORECAST TO RAISE WINDS AND HIGH
TEMPERATURES AND TO ADJUST THE CLOUD COVER.
&&
.AVIATION...GUSTY SOUTHWEST WINDS WILL BECOME NORTHWEST TODAY. VFR
CONDITIONS WILL PREVAIL THROUGH THE FORECAST PERIOD.
&&
.PREV DISCUSSION... /ISSUED 243 AM MST SAT NOV 21 2009/
DISCUSSION...09Z SURFACE ANALYSIS HAD WEAK LOW OVER NORTHEASTERN
WY. FAIRLY TIGHT GRADIENT NEAR LOW WITH GUSTY WINDS IN WY AND
PORTIONS OF THE BLACK HILLS ABOVE THE INVERSION. WILL LEAVE
ADVISORY IN PLACE UNTIL 600 AM. FOR TODAY...UPPER TROUGH OVER THE
ROCKIES MOVES EAST DRAGGING COLD FRONT THROUGH THE CWA...WASHING
OUT LATE. MOST HIGHS WILL OCCUR THIS MORNING WITH WEAK COLD AIR
ADVECTION IN THE AFTERNOON. FOR TONIGHT...WEAK HIGH SLIPS THROUGH.
HAVE DROPPED POPS GIVEN DRY NATURE OF LOWER TROPOSPHERE.
SUNDAY...VERY TRANSIENT SHORTWAVE RIDGE OVER THE CWA WILL GIVE WAY
TO FAST MOVING SHORTWAVE SUNDAY NIGHT. SURFACE HIGH QUICKLY SHIFTS
SOUTH WITH RETURN FLOW OVER WESTERN PORTIONS OF THE CWA. DRY
DURING THE DAY...BUT ENOUGH FORCING/MOISTURE PRESENT FOR LOW POPS
SUNDAY NIGHT. TEMPERATURES NEAR GUIDANCE.
MONDAY...SOME DIFFERENCES IN MODEL HANDLING OF SHORTWAVE TROUGH.
00Z NAM/ECMWF/GEM TRENDING SOUTH AND EAST. 00Z GFS MORE NORTHERLY
TRACK. WILL GO WITH MODEL TRENDS AT THIS POINT...WHICH WILL KEEP
BEST PRECIPITATION AWAY FROM THE CWA.
EXTENDED...AFOREMENTIONED SYSTEM WILL CONTINUE ITS DEPARTURE ON
TUESDAY...WITH SOME PRECIP POSSIBLY LINGERING OVER SOUTH CENTRAL
SOUTH DAKOTA. GFS BRINGS NEXT WAVE THROUGH THE REGION TUESDAY
NIGHT...THOUGH HAS HAD SOME TROUBLE WITH THE PLACEMENT OF THIS
SYSTEM OVER THE PAST FEW RUNS. THEREFORE...HAVE LIMITED LOW POPS
TO THE EASTERN/NRN CWFA. RIDGE STARTS BUILDING IN FOR MID-WEEK
BRINGING A RETURN TO DRY CONDITIONS.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&
$$
000
FXUS65 KCYS 211626
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
926 AM MST SAT NOV 21 2009
.UPDATE...HAVE ISSUED LOCAL HIGH WIND WARNING FOR ARLINGTON AREA OF
SOUTH CENTRAL WY UNTIL 19Z. SUSTAINED SPEEDS OF 40 MPH HAVE BEEN
OCCURRING THERE SINCE 1430Z WITH ONE GUST TO 60 MPH AROUND THEN AND
MORE TO 65 MPH CURRENTLY. WINDS SHOULD SLOWLY DECREASE BEHIND A
COLD FRONT BY MID AFTERNOON. JLH
&&
.PREV DISCUSSION... /ISSUED 300 AM MST SAT NOV 21 2009/
SHORT TERM...TODAY THROUGH SUNDAY NIGHT
AN ACTIVE PERIOD WILL BE IN STORE FOR THE CWA THROUGH 12Z MONDAY.
A SHORTWAVE TROUGH CURRENTLY OVER THE PACIFIC NORTHWEST WILL MOVE
EAST AND ACROSS THE CWA THROUGH 18Z SUNDAY. MODELS HAVE BEEN
TRENDING A BIT SLOWER WITH THE FEATURE THE PAST FEW RUNS BUT ARE
NOW FAIRLY CLOSE WITH THE AXIS OVER FAR EASTERN WYOMING AT 12Z
SUNDAY. THE ASSOCIATED PACIFIC COLD FRONT WAS LOCATED FROM
WESTERN MONTANA TO IDAHO EARLY THIS MORNING WITH 2 TO 3 MB THREE
HOURLY SURFACE PRESSURE RISES BEHIND THE FRONT. THE FRONT WILL
MOVE ACROSS THIS AFTERNOON AND EARLY EVENING. CONSIDERABLE MID
AND HIGH CLOUDS WILL BE OVER THE CWA TODAY AND TONIGHT PRIOR TO
THE PASSAGE OF THE SHORTWAVE TROUGH. IT WILL ALSO BE WINDY OVER
AND NEAR THE MOUNTAINS TODAY WITH THE SURFACE LOW PRESSURE TROUGH
OVER FAR EASTERN WYOMING. WIND GUSTS SINCE 06Z HAVE BEEN AS HIGH
AS 52 MPH AT KCPR...KARL AND KRWL. THE WIND SPEEDS MAY BE THE
HIGHEST THROUGH THE MORNING WITH THE TEMPERATURE INVERSION
PRESENT AND BASED AROUND 750 MB. TEMPERATURES ARE CURRENTLY FAIRLY
MILD IN MANY LOCATIONS AND WILL HELP TO PRODUCE ANOTHER DAY WITH
ABOVE NORMAL TEMPERATURES OVER THE EASTERN PART OF THE CWA AHEAD
OF THE FRONT. THERE IS CURRENTLY BANDS OF PRECIPITATION ON THE
KMTX AND KSFX RADARS ASSOCIATED WITH THE BAROCLINIC CLOUD BAND NOW
OVER EASTERN IDAHO AND NORTHERN UTAH. THE MAIN THREAT OF LIGHT
SNOW WILL BE OVER AND NEAR THE SNOWY RANGE TONIGHT WITH THE
PASSAGE OF THE SHORTWAVE TROUGH. OTHERWISE EXPECT MOST OF THE CWA
TO REMAIN DRY. MODELS DIFFER ON THE TIMING AND AMPLITUDE OF THE
NEXT SHORTWAVE TROUGH. THE FEATURE WILL DEEPEN OVER THE ROCKIES
SUNDAY NIGHT WITH THE ASSOCIATED SURFACE COLD FRONT MOVING ACROSS
THE CWA SUNDAY NIGHT. THE 00Z ECMWF CONTINUES TO BE SLOWER THAN
MOST OF THE OTHER MODELS WITH THE SHORTWAVE TROUGH BUT HAS TRENDED
FASTER AND WITH LESS AMPLITUDE THAN ITS 12Z RUN. THE 00Z ECMWF IS
FAVORED BY HPC AND SO WILL USE THAT MODEL AGAIN FOR THIS
FORECAST... ESPECIALLY SUNDAY NIGHT. THE LEFT EXIT REGION OF THE
300 MB JET WILL AFFECT MAINLY THE SOUTH PART OF THE CWA SUNDAY
NIGHT AND MOISTURE WILL INCREASE. FOR NOW WILL CONTINUE THE TREND
OF INCREASING POPS AND SNOW AMOUNTS OVER THE CWA FOR SUNDAY NIGHT.
TWO TO FIVE INCHES OF NEW SNOW ARE POSSIBLE IN THE SNOWY RANGE
SUNDAY NIGHT...WITH AN INCH OR LESS OVER MOST OF THE REST OF THE
SOUTH PART OF THE CWA.
LONG TERM...MONDAY THROUGH FRIDAY
LEANED TOWARDS THE 00Z ECMWF AS IT SEEMS TO BE HANDLING THE SPLIT
FLOW BETTER THAN THE GFS...GEMS OR UKMET. THE UPPER TROUGH WILL
MOVE ACROSS THE CWA ON MON...WITH THE AXIS MOVING EAST OF THE
FORECAST AREA BY EVENING. AN UPPER LOW WILL FORM OVER THE CENTRAL
PLAINS MON NIGHT. COLD TEMPERATURES CAN BE EXPECTED ACROSS THE AREA
MON WITH BRISK WINDS IN THE MORNING. SOME LIGHT SNOW WILL FALL
ACROSS THE AREA...WITH THE BEST CHANCES IN THE MOUNTAINS...BUT
LOWERED POPS DUE TO BEST DYNAMICS SHIFTING EAST AS THE TROUGH AXIS
MOVES FAIRLY QUICK ACROSS THE CWA DURING THE DAY. AN INCH OR TWO
ADDITIONAL SNOW WILL FALL IN THE MOUNTAINS...WITH LESS THAN AN INCH
AT THE LOWER ELEVATIONS. ON TUES...NW FLOW WILL SET UP ALOFT AS AN
UPPER RIDGE BUILD OVER THE WESTERN U.S. DRY CONDITIONS WILL PERSIST
FROM TUES THROUGH FRIDAY. TEMPERATURES WILL MODERATE A FEW DEGREES
ON TUESDAY UNDER PARTLY CLOUDY SKIES. FOR WED...MILD CONDITIONS
WILL OCCUR AND THEN VERY MILD FOR THUR AND FRI WITH DOWNSLOPE WINDS
AND SUNNY SKIES. THE NW UPPER FLOW WILL FLATTEN OUT FRI AS AN UPPER
TROUGH MOVES INLAND FROM THE WEST COAST. A COLD FRONT WILL MOVE
ACROSS THE CWA LATE FRI NIGHT/EARLY SAT MORNING. HIGH TEMPERATURES
WILL BE FROM 5 TO 8 DEGREES BELOW NORMAL MON...AROUND NORMAL TUES
AND WED...AND 5 TO 8 DEGREES ABOVE NORMAL FOR THANKSGIVING DAY AND
THE FRIDAY HOLIDAY SHOPPING DAY.
AVIATION...
VFR CONDITIONS WILL CONTINUE OVER THE CWA TODAY. CLOUD BASES WILL
LOWER TONIGHT BUT SHOULD STILL REMAIN VFR. THE SNOWY RANGE WILL BE
OBSCURED TONIGHT. WEST WINDS WILL GUST AS HIGH AS 50 MPH THROUGH
MID MORNING OVER AND NEAR THE MOUNTAINS. THOSE WINDS WILL PRODUCE
TURBULENT CONDITIONS AT AIRPORTS SUCH AS KRWL...KLAR...KDGW...KEAN
AND KCYS. CLOUDS WILL ONCE AGAIN LOWER SUNDAY NIGHT OVER THE CWA
WITH AT LEAST PERIODS OF MVFR CEILINGS AND VISIBILITIES IN SNOW
OVER THE SOUTH PART OF THE CWA. THE SNOWY RANGE WILL BE OBSCURED
AGAIN SUNDAY NIGHT. ICING WILL BE A CONCERN WITH COOLER
TEMPERATURES AND INCREASED MOISTURE.
FIRE WEATHER...
WESTERLY SURFACE WINDS WILL GUST AS HIGH AS 50 MPH OVER AND NEAR THE
MOUNTAINS THROUGH MID MORNING. LOWER WIND SPEEDS ARE THEN EXPECTED
THROUGH SUNDAY. MINIMUM RELATIVE HUMIDITIES WILL BE BETWEEN 23
AND 30 PERCENT THIS AFTERNOON AND AGAIN SUNDAY AFTERNOON. EVEN
WITH THE GUSTY WINDS...FIRE WEATHER CONCERNS WILL BE MINIMAL FOR
THIS WEEKEND.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...HIGH WIND WARNING UNTIL NOON SATURDAY FOR WYZ110.
NE...NONE.
&&
$$
SHORT TERM/AVIATION...WEILAND
LONG TERM...KMD
000
FXUS65 KCYS 211000 AAA
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
300 AM MST SAT NOV 21 2009
.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
AN ACTIVE PERIOD WILL BE IN STORE FOR THE CWA THROUGH 12Z MONDAY.
A SHORTWAVE TROUGH CURRENTLY OVER THE PACIFIC NORTHWEST WILL MOVE
EAST AND ACROSS THE CWA THROUGH 18Z SUNDAY. MODELS HAVE BEEN
TRENDING A BIT SLOWER WITH THE FEATURE THE PAST FEW RUNS BUT ARE
NOW FAIRLY CLOSE WITH THE AXIS OVER FAR EASTERN WYOMING AT 12Z
SUNDAY. THE ASSOCIATED PACIFIC COLD FRONT WAS LOCATED FROM
WESTERN MONTANA TO IDAHO EARLY THIS MORNING WITH 2 TO 3 MB THREE
HOURLY SURFACE PRESSURE RISES BEHIND THE FRONT. THE FRONT WILL
MOVE ACROSS THIS AFTERNOON AND EARLY EVENING. CONSIDERABLE MID
AND HIGH CLOUDS WILL BE OVER THE CWA TODAY AND TONIGHT PRIOR TO
THE PASSAGE OF THE SHORTWAVE TROUGH. IT WILL ALSO BE WINDY OVER
AND NEAR THE MOUNTAINS TODAY WITH THE SURFACE LOW PRESSURE TROUGH
OVER FAR EASTERN WYOMING. WIND GUSTS SINCE 06Z HAVE BEEN AS HIGH
AS 52 MPH AT KCPR...KARL AND KRWL. THE WIND SPEEDS MAY BE THE
HIGHEST THROUGH MID MORNING WITH THE TEMPERATURE INVERSION PRESENT
AND BASED AROUND 750 MB. TEMPERATURES ARE CURRENTLY FAIRLY MILD
IN MANY LOCATIONS AND WILL HELP TO PRODUCE ANOTHER DAY WITH ABOVE
NORMAL TEMPERATURES OVER THE EASTERN PART OF THE CWA AHEAD OF THE
FRONT. THERE IS CURRENTLY BANDS OF PRECIPITATION ON THE KMTX AND
KSFX RADARS ASSOCIATED WITH THE BAROCLINIC CLOUD BAND NOW OVER
EASTERN IDAHO AND NORTHERN UTAH. THE MAIN THREAT OF LIGHT SNOW
WILL BE OVER AND NEAR THE SNOWY RANGE TONIGHT WITH THE PASSAGE OF
THE SHORTWAVE TROUGH. OTHERWISE EXPECT MOST OF THE CWA TO REMAIN
DRY. MODELS DIFFER ON THE TIMING AND AMPLITUDE OF THE NEXT
SHORTWAVE TROUGH. THE FEATURE WILL DEEPEN OVER THE ROCKIES SUNDAY
NIGHT WITH THE ASSOCIATED SURFACE COLD FRONT MOVING ACROSS THE CWA
SUNDAY NIGHT. THE 00Z ECMWF CONTINUES TO BE SLOWER THAN MOST OF
THE OTHER MODELS WITH THE SHORTWAVE TROUGH BUT HAS TRENDED FASTER
AND WITH LESS AMPLITUDE THAN ITS 12Z RUN. THE 00Z ECMWF IS FAVORED
BY HPC AND SO WILL USE THAT MODEL AGAIN FOR THIS FORECAST...
ESPECIALLY SUNDAY NIGHT. THE LEFT EXIT REGION OF THE 300 MB JET
WILL AFFECT MAINLY THE SOUTH PART OF THE CWA SUNDAY NIGHT AND
MOISTURE WILL INCREASE. FOR NOW WILL CONTINUE THE TREND OF
INCREASING POPS AND SNOW AMOUNTS OVER THE CWA FOR SUNDAY NIGHT.
TWO TO FIVE INCHES OF NEW SNOW ARE POSSIBLE IN THE SNOWY RANGE
SUNDAY NIGHT...WITH AN INCH OR LESS OVER MOST OF THE REST OF THE
SOUTH PART OF THE CWA.
.LONG TERM...MONDAY THROUGH FRIDAY
LEANED TOWARDS THE 00Z ECMWF AS IT SEEMS TO BE HANDLING THE SPLIT
FLOW BETTER THAN THE GFS...GEMS OR UKMET. THE UPPER TROUGH WILL
MOVE ACROSS THE CWA ON MON...WITH THE AXIS MOVING EAST OF THE
FORECAST AREA BY EVENING. AN UPPER LOW WILL FORM OVER THE CENTRAL
PLAINS MON NIGHT. COLD TEMPERATURES CAN BE EXPECTED ACROSS THE AREA
MON WITH BRISK WINDS IN THE MORNING. SOME LIGHT SNOW WILL FALL
ACROSS THE AREA...WITH THE BEST CHANCES IN THE MOUNTAINS...BUT
LOWERED POPS DUE TO BEST DYNAMICS SHIFTING EAST AS THE TROUGH AXIS
MOVES FAIRLY QUICK ACROSS THE CWA DURING THE DAY. AN INCH OR TWO
ADDITIONAL SNOW WILL FALL IN THE MOUNTAINS...WITH LESS THAN AN INCH
AT THE LOWER ELEVATIONS. ON TUES...NW FLOW WILL SET UP ALOFT AS AN
UPPER RIDGE BUILD OVER THE WESTERN U.S. DRY CONDITIONS WILL PERSIST
FROM TUES THROUGH FRIDAY. TEMPERATURES WILL MODERATE A FEW DEGREES
ON TUESDAY UNDER PARTLY CLOUDY SKIES. FOR WED...MILD CONDITIONS
WILL OCCUR AND THEN VERY MILD FOR THUR AND FRI WITH DOWNSLOPE WINDS
AND SUNNY SKIES. THE NW UPPER FLOW WILL FLATTEN OUT FRI AS AN UPPER
TROUGH MOVES INLAND FROM THE WEST COAST. A COLD FRONT WILL MOVE
ACROSS THE CWA LATE FRI NIGHT/EARLY SAT MORNING. HIGH TEMPERATURES
WILL BE FROM 5 TO 8 DEGREES BELOW NORMAL MON...AROUND NORMAL TUES
AND WED...AND 5 TO 8 DEGREES ABOVE NORMAL FOR THANKSGIVING DAY AND
THE FRIDAY HOLIDAY SHOPPING DAY.
&&
.AVIATION...
VFR CONDITIONS WILL CONTINUE OVER THE CWA TODAY. CLOUD BASES WILL
LOWER TONIGHT BUT SHOULD STILL REMAIN VFR. THE SNOWY RANGE WILL BE
OBSCURED TONIGHT. WEST WINDS WILL GUST AS HIGH AS 50 MPH THROUGH
MID MORNING OVER AND NEAR THE MOUNTAINS. THOSE WINDS WILL PRODUCE
TURBULENT CONDITIONS AT AIRPORTS SUCH AS KRWL...KLAR...KDGW...KEAN
AND KCYS. CLOUDS WILL ONCE AGAIN LOWER SUNDAY NIGHT OVER THE CWA
WITH AT LEAST PERIODS OF MVFR CEILINGS AND VISIBILITIES IN SNOW
OVER THE SOUTH PART OF THE CWA. THE SNOWY RANGE WILL BE OBSCURED
AGAIN SUNDAY NIGHT. ICING WILL BE A CONCERN WITH COOLER
TEMPERATURES AND INCREASED MOISTURE.
&&
.FIRE WEATHER...
WESTERLY SURFACE WINDS WILL GUST AS HIGH AS 50 MPH OVER AND NEAR THE
MOUNTAINS THROUGH MID MORNING. LOWER WIND SPEEDS ARE THEN EXPECTED
THROUGH SUNDAY. MINIMUM RELATIVE HUMIDITIES WILL BE BE BETWEEN 23
AND 30 PERCENT THIS AFTERNOON AND AGAIN SUNDAY AFTERNOON. EVEN
WITH THE GUSTY WINDS...FIRE WEATHER CONCERNS WILL BE MINIMAL FOR
THIS WEEKEND.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...NONE.
NE...NONE.
&&
$$
SHORT TERM...WEILAND
LONG TERM...KMD
000
FXUS65 KRIW 210959
AFDRIW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
259 AM MST SAT NOV 21 2009
.SHORT TERM...TODAY THROUGH MONDAY NIGHT
THE BAROCLINIC LEAF HAS MOVED INTO WESTERN WYOMING THIS
MORNING...THOUGH CLOUD TOPS CONTINUE TO WARM BASED ON CURRENT
SATELLITE IMAGERY. RADAR REFLECTIVITIES NOTED OVER CENTRAL AND
EASTERN IDAHO THIS MORNING...WITH SHOWERS CONTINUING TO PROGRESS
TOWARDS WESTERN WYOMING. EXPECT SNOWFALL TO DEVELOP OVER THE WESTERN
MOUNTAINS AND VALLEYS THIS MORNING...AND CONTINUE THROUGH THE
AFTERNOON HOURS. THE TROUGH ASSOCIATED WITH THE BAROCLINIC LIFT SEES
ITS AXIS MOVE INTO WESTERN WYOMING BY LATE THIS AFTERNOON...WITH
SHOWER ACTIVITY WEAKENING AS THE AXIS PASSES. THE MAJORITY OF
MOISTURE ASSOCIATED WITH THIS FEATURE WILL DRAIN OVER THE WESTERN
VALLEYS AND MOUNTAINS...AS WELL AS A FEW SNOWFLAKES OVER THE BIG
HORN MOUNTAINS. NOT EXPECTING MUCH OF ANY WEATHER FOR AREAS EAST OF
THE CONTINENTAL DIVIDE...OTHER THAN CONTINUED CLOUDINESS.
THE TROUGH AXIS WILL MOVE EAST OF THE CWA LATE SATURDAY NIGHT INTO
EARLY SUNDAY MORNING...WITH A BRIEF TRANSITORY RIDGE BUILDING OVER
THE AREA. ON THE HEELS OF THE EXITING TROUGH WILL BE
ANOTHER...STRONGER AREA OF LOW PRESSURE WHICH WILL MOVE INTO THE
INTERMOUNTAIN WEST BY THE MID MORNING HOURS OF SUNDAY. THIS SECOND
TROUGH HAS TAKEN MORE OF A NEGATIVE TILT IN RECENT MODEL RUNS...THE
INTRODUCTION OF CONVECTIVELY BASED SNOWFALL WILL ALLOW FOR THE
POTENTIALLY FOR BRIEF...HEAVIER SNOW SHOWERS. THIS SYSTEM WILL ALSO
BRING IN CONTINUALLY COOLING H7 TEMPERATURES...WITH COOLING DAYTIME
HIGH TEMPERATURES EXPECTED FOR THE LATTER HALF OF THE WEEKEND AND
INTO THE WORK WEEK. SNOW AND RAIN ASSOCIATED WITH THIS SYSTEM WILL
BECOME MORE WIDESPREAD SUNDAY EVENING...MOVING EAST OF THE DIVIDE TO
POTENTIALLY IMPACT MUCH OF THE STATE WITH AT LEAST BRIEF LIGHT SNOW.
THE AXIS WITH THIS TROUGH WILL MOVE INTO CENTRAL WYOMING LATE
SUNDAY...AND MOVE THROUGH THE CWA BY EARLY MONDAY AFTERNOON. MOIST
NORTHWEST FLOW WILL MOVE OVER THE AREA AS THIS SYSTEM DEPARTS...WITH
SOME WRAPAROUND MOISTURE CONTINUING LIGHT SNOWFALL OVER NORTHERN
WYOMING INTO MONDAY EVENING. AS WRAPAROUND MOVES FURTHER
EAST...ANOTHER RIDGE WILL BUILD OVER THE AREA...HELPING TO WEAKEN
SNOW AND RAIN MONDAY NIGHT.
.LONG TERM...TUESDAY THROUGH SATURDAY
DRY CONDITIONS WITH A WARMING TREND ARE EXPECTED TUESDAY THROUGH
THANKSGIVING DAY. THE NEXT PACIFIC STORM SYSTEM WILL BRING A CHANCE
OF SNOW TO THE WEST FRIDAY AND COOLER CONDITIONS WITH CHANCES OF
SNOW ACROSS CENTRAL WYOMING FRIDAY NIGHT AND SATURDAY.
LATEST ECMWF SHOWING A SOLUTION SIMILAR TO LAST FEW GEM RUNS WITH A
CLIPPER DIVING DOWN FRONT SIDE OF INTERMOUNTAIN WEST UPPER RIDGE
INTO BACKSIDE OF UPPER LOW OVER UPPER MISSISSIPPI VALLEY TUESDAY AND
TUESDAY NIGHT...KEEPING SYSTEM WELL NORTH AND EAST OF WYOMING.
GFS...SHOWING A STRONGER CLIPPER DIVING INTO THE NORTHERN
PLAINS...IS ALSO TRENDING IN THIS DIRECTION. FORECAST SIDES WITH
ECMWF AND GEM RESULTING IN A DRY FORECAST TUESDAY WITH HIGH
TEMPERATURES AROUND 10F WARMER THAN MONDAY...OR UPPER 30S TO NEAR 50
MOST BASINS AND VALLEYS. UPPER RIDGE EXPANDS ACROSS AREA WEDNESDAY
AND THANKSGIVING DAY WITH DRY AND UNSEASONABLY MILD HIGH
TEMPERATURES THOUGH VALLEY INVERSIONS WILL CONTINUE TO KEEP
TEMPERATURES 10F-15F BELOW FULL MIXING POTENTIAL AS HAS BEEN THE
CASE WITH THE LAST FEW DAYS OF CLEAR SKIES/LIGHT WIND. NIGHTTIME
LOWS WILL BE MORE NEAR NORMAL WITH GOOD RADIATIONAL COOLING. MODEL
SPREAD INCREASES FRIDAY AND SATURDAY WITH GFS CONTINUING TO HANDLE
SPLIT FLOW OF LAST FEW WEEKS POORLY...TOO FAR NORTH AND TOO
PROGRESSIVE WITH INCOMING PACIFIC ENERGY. ECMWF SPLITS NEXT PACIFIC
SYSTEM ALONG WEST COAST FRIDAY MORNING WITH MOST OF THIS ENERGY
DIVING INTO THE GREAT BASIN FRIDAY NIGHT. ECMWF IS LIKELY NOT
PROGRESSIVE ENOUGH...HOLDING A CLOSED LOW BACK OVER AZ/NM INTO
SUNDAY. FORECAST BRINGS IN CHANCES OF PRECIPITATION INTO THE WEST
FRIDAY...SPREADING EAST OF THE DIVIDE FRIDAY NIGHT AND SATURDAY
ALONG WITH COOLER TEMPERATURES MORE NEAR SEASONAL NORMALS.
&&
.AVIATION...
A COLD FRONT WILL MOVE THROUGH THE AREA TODAY. WINDY WEATHER WILL BE
COMMON ACROSS MUCH OF THE REGION...WITH SPEEDS OF 20 TO 30 KNOTS
WITH GUSTS TO 35 KNOTS. WIND SPEEDS WILL DIMINISH TO 10 TO 15 KNOTS
AFTER 00Z SUN IN MOST LOCATIONS. SNOW WILL OCCUR IN THE MOUNTAINS
AND PARTS OF THE FAR WEST THROUGH 18Z...THEN COVERAGE WILL DECREASE
AFTER 18Z. MVFR TO IFR CONDITIONS WILL OCCUR IN AREAS OF SNOW IN
WESTERN WY THROUGH 21Z...THEN VFR TO MVFR CONDITIONS ARE EXPECTED
WITH SCATTERED SNOW SHOWERS THROUGH 00Z SUN. EXPECT WIDESPREAD MOUNTAIN
OBSCURATION THROUGH 21Z...THEN MAINLY MOUNTAIN TOP OBSCURATION
THROUGH 00Z SUN. EAST OF THE CONTINENTAL DIVIDE...VFR CONDITIONS
WILL OCCUR TODAY THROUGH 06Z SUN.
&&
.FIRE WEATHER...
SNOWFALL EXPECTED OVER THE WESTERN MOUNTAINS AND VALLEYS TODAY. THE
PASSAGE OF A COLD FRONT THROUGH THE STATE WILL BRING COOLER
TEMPERATURES ACROSS MUCH OF THE AREA TODAY...WITH INCREASED CLOUD
COVER. SNOW AND RAIN ARE EXPECTED TO WEAKEN THIS AFTERNOON...WITH A
VERY BRIEF PERIOD OF HIGH PRESSURE ANTICIPATED TONIGHT. THE NEXT
APPROACHING SYSTEM FOR SUNDAY LOOKS STRONGER THAN THE CURRENT
SYSTEM...WITH FORECAST MODELS INDICATING SOME INSTABILITY AND
POSSIBLY CONVECTIVE SNOW FALL OVER PORTIONS OF THE AREA.
TEMPERATURES WILL CONTINUE TO COOL THROUGH THE WEEKEND AND INTO
EARLY NEXT WEEK. WIND WILL REMAIN ELEVATED TODAY AND ARE EXPECTED TO
WEAKEN TONIGHT. HOWEVER...THE ARRIVAL OF THE SECOND SYSTEM WILL
AGAIN CAUSE A TIGHTENED PRESSURE GRADIENT OVER CENTRAL WYOMING
RESULTING IN INCREASED WIND SUNDAY EVENING.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...BRANHAM
LONG TERM...AEM
AVIATION...AR
FIRE WEATHER...BRANHAM
000
FXUS63 KUNR 210943
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
243 AM MST SAT NOV 21 2009
.DISCUSSION...09Z SURFACE ANALYSIS HAD WEAK LOW OVER NORTHEASTERN
WY. FAIRLY TIGHT GRADIENT NEAR LOW WITH GUSTY WINDS IN WY AND
PORTIONS OF THE BLACK HILLS ABOVE THE INVERSION. WILL LEAVE
ADVISORY IN PLACE UNTIL 600 AM. FOR TODAY...UPPER TROUGH OVER THE
ROCKIES MOVES EAST DRAGGING COLD FRONT THROUGH THE CWA...WASHING
OUT LATE. MOST HIGHS WILL OCCUR THIS MORNING WITH WEAK COLD AIR
ADVECTION IN THE AFTERNOON. FOR TONIGHT...WEAK HIGH SLIPS THROUGH.
HAVE DROPPED POPS GIVEN DRY NATURE OF LOWER TROPOSPHERE.
SUNDAY...VERY TRANSIENT SHORTWAVE RIDGE OVER THE CWA WILL GIVE WAY
TO FAST MOVING SHORTWAVE SUNDAY NIGHT. SURFACE HIGH QUICKLY SHIFTS
SOUTH WITH RETURN FLOW OVER WESTERN PORTIONS OF THE CWA. DRY
DURING THE DAY...BUT ENOUGH FORCING/MOISTURE PRESENT FOR LOW POPS
SUNDAY NIGHT. TEMPERATURES NEAR GUIDANCE.
MONDAY...SOME DIFFERENCES IN MODEL HANDLING OF SHORTWAVE TROUGH.
00Z NAM/ECMWF/GEM TRENDING SOUTH AND EAST. 00Z GFS MORE NORTHERLY
TRACK. WILL GO WITH MODEL TRENDS AT THIS POINT...WHICH WILL KEEP
BEST PRECIPITATION AWAY FROM THE CWA.
EXTENDED...AFOREMENTIONED SYSTEM WILL CONTINUE ITS DEPARTURE ON
TUESDAY...WITH SOME PRECIP POSSIBLY LINGERING OVER SOUTH CENTRAL
SOUTH DAKOTA. GFS BRINGS NEXT WAVE THROUGH THE REGION TUESDAY
NIGHT...THOUGH HAS HAD SOME TROUBLE WITH THE PLACEMENT OF THIS
SYSTEM OVER THE PAST FEW RUNS. THEREFORE...HAVE LIMITED LOW POPS
TO THE EASTERN/NRN CWFA. RIDGE STARTS BUILDING IN FOR MID-WEEK
BRINGING A RETURN TO DRY CONDITIONS.
&&
.AVIATION...GUSTY SOUTHWEST WINDS OVER THE NRN AND NERN FOOTHILLS OF
THE BLKHLS AND OVER NERN WY WILL DIMINISH THIS MORNING. VFR
CONDITIONS WILL PREVAIL THROUGH THE FORECAST PERIOD.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WIND ADVISORY UNTIL 6 AM MST EARLY THIS MORNING FOR NORTHERN
FOOT HILLS-STURGIS/PIEDMONT FOOT HILLS.
WY...NONE.
&&
$$
HELGESON/SCHILD
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