000
FXUS63 KDMX 051821 AAB
AFDDMX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE DES MOINES IA
1250 PM CDT FRI SEP 5 2008

UPDATED AVIATION DISCUSSION

.SHORT TERM.../TODAY/
CENTRAL IOWA...CLEAR AND CALM...THIS MORNING IS EXPERIENCING AREAS
OF FOG...SOME OF WHICH ARE DENSE. WILL ISSUE A DENSE FOG ADVISORY
FOR THE EASTERN HALF OR SO OF THE CWA EARLY THIS MORNING SINCE
MORE AND MORE OBS ARE COMING IN WITH VSBY ONE HALF MILE OR LESS.
OTHERWISE...A WEAK SURFACE LOW PRESSURE CENTER NEAR FARGO AT
06Z...WITH A WARM FRONT EXTENDING SOUTH NEAR THE NEB/IA BORDER AND
COLD FRONT WEST ACROSS SOUTH DAKOTA...WILL ALL MOVE SLOWLY EAST
TODAY. RAIN HAS BROKEN OUT OVER THE CENTRAL HIGH PLAINS AS A
RESULT OF SYNOPTIC SCALE FORCING AHEAD OF DIGGING SHORTWAVE.
SURFACE CONVERGENCE WILL BE WEAK TO NIL AND AIRMASS BELOW 5000 FT
WILL BE RATHER DRY TODAY...SO WILL NEED TO RELY ON QG FORCING WITH
UPPER LEVEL WAVE TO GENERATE SHOWERS. FORCING IS STRONGEST ACROSS
WESTERN IOWA...BUT WEAKENS AS IT MOVES EAST. SO WILL GO WITH
LIKELY SHOWERS AFTER NOON IN THE WEST...TAPERING TO SLIGHT CHANCES
IN THE EAST. DESPITE THE COOL START...A FAIR AMOUNT OF SUNSHINE
AND WEAK WARM ADVECTION THIS MORNING SHOULD HELP BOOST TEMPS
QUICKLY BEFORE CLOUDS INCREASE FOR THE LATE IN THE MORNING AND
EARLY AFTERNOON. MODEL SOUNDINGS INDICATE A MODESTLY DEEP
ADIABATIC LAPSE RATE BY EARLY AFTERNOON...SO WENT A LITTLE WARMER
THAN COOLER MET GUIDANCE.

.LONG TERM.../TONIGHT THROUGH THURSDAY/
COOL AND CLOUDY PATTERN WILL CONTINUE THROUGH THE WEEKEND AS WE
REMAIN WITHIN BROAD CYCLONIC FLOW ALOFT. SHORTWAVE PULSES ROTATING
THROUGH THIS FLOW WILL PRODUCE PERIODS OF SHOWERS OVER THE NEXT
SEVERAL DAYS...HOWEVER PINNING DOWN LOCATIONS OF HIGHEST RAIN
CHANCES IS PROBLEMATIC DUE TO POOR FORECAST MODEL RESOLUTION OF
SUCH SMALL FEATURES. THERE IS A CHANCE OF SHOWERS MAINLY IN THE
NORTHEAST THIS EVENING AS THE FIRST SHORTWAVE DEPARTS. NEXT WEAK
IMPULSE SHOULD COME THROUGH SATURDAY NIGHT AND SUNDAY...WITH A
SURFACE TROUGH STALLING OUT OVER NORTHERN MISSOURI AND BRINGING
ENHANCED RAIN CHANCES IN THE SOUTH LATE SUNDAY AND SUNDAY NIGHT. A
STRONGER WAVE WILL PUSH A REINFORCING COLD FRONT THROUGH THE STATE
ON MONDAY...CLEARING US OUT MONDAY NIGHT THROUGH TUESDAY. WITH
CLEARING SKIES BEHIND THIS FRONT AND THERMAL TROUGH OVERHEAD
MONDAY NIGHT...THERE IS A POTENTIAL FOR FROSTING CONDITIONS
PARTICULARLY IN THE NORTHWEST. HAVE MAINTAINED A FEW UPPER 30S
TEMPS IN THIS AREA...AND GIVEN MODEL TRENDS THESE NUMBERS COULD
COME DOWN FURTHER YET. ANOTHER STORM SYSTEM WILL APPROACH ON
WEDNESDAY...PROVIDING RENEWED CHANCES FOR PRECIPITATION WITH
HEAVIER RAIN POSSIBLE GIVEN GOOD RETURN FLOW AHEAD OF THE SYSTEM.

&&

.AVIATION...05/18Z
UPSTREAM SYSTEM WILL MOVE ACROSS TAF SITES BETWEEN 19Z AND 02Z.
MAINLY VFR CLOUD COVER AND VSBYS WITH THIS SYSTEM.  HOWEVER...LOCAL
MVFR CONDITIONS ARE POSSIBLE IF THE SHOWERS BECOME A LITTLE HEAVIER
THAN CURRENT RADAR TRENDS ARE INDICATING.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...FAB
LONG TERM...LEE
AVIATION...FAB