000
FXUS63 KOAX 211949
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
249 PM CDT THU AUG 21 2008
.DISCUSSION...
MAIN FORECAST CHALLENGE WILL BE THE NEXT FRONTAL BOUNDARY MOVING
INTO THE AREA ON FRIDAY AND ITS IMPACT ON LOCAL WEATHER OVER THE
NEXT FEW DAYS.
IN THE MEANTIME...UPPER TROUGH NOTED ACROSS THE PLAINS CONTINUES
TO SHIFT EAST TODAY WITH LATEST WATER VAPOR IMAGERY/88D MOSAIC
INDICATING ALL MEASURABLE PRECIP REMAINS WELL EAST OF THE CWA.
LINGERING SPOTTY DRIZZLE HAS ALL BUT ENDED WITH JUST SOME CLOUDS
REMAINING ACROSS THE REGION WITH TEMPS IN THE UPPER 60S TO MID
70S. FEEL THAT THESE CLOUDS COULD SCATTER OUT A BIT THIS EVENING...
BUT THEN PROBABLY FILL BACK IN AFTER MIDNIGHT WITH SOME STATUS
DEVELOPING BY DAYBREAK BASED ON LOW LEVEL HUMIDITY PROGS. WAS ALSO
SOMEWHAT CONCERNED WITH FOG DEVELOPMENT GIVEN ONLY A DEGREE OR TWO
TEMP/DEWPOINT SPREADS. HOWEVER...TIGHTENING PRESSURE GRADIENT IN
RESPONSE TO ADVANCING FRONT SHOULD HELP TO KEEP THE BOUNDARY LAYER
MIXED ENOUGH FOR MOST AREAS...EXCEPT SOUTHEAST NEBRASKA AND
SOUTHWEST IOWA WHERE AREAS OF FOG MAY DEVELOP...WHICH COULD BE
LOCALLY DENSE IN AREAS FROM KFNB TO KICL...AND POSSIBLY EVEN
LOCALLY AT KTQE.
MODELS ARE IN PRETTY GOOD AGREEMENT WITH THE FRONT MOVING FROM
NORTHWEST TO SOUTHEAST FRIDAY AFTERNOON AND EVENING. HEALTHY CAP IN
PLACE ALONG AND AHEAD OF THE FRONT SHOULD HOLD OFF DEVELOPMENT
UNTIL MID TO LATE AFTERNOON NORTH OF I80...THEN WITH DECENT PRECIP
CHANCES FRIDAY EVENING AS CAP WEAKENS ALOFT. WHILE INSTABILITY
APPEARS MODEST...BULK SHEAR IS NOT THAT IMPRESSIVE RESULTING IN
SCATTERED MULTI CELLS WITH JUST AN ISOLATED SEVERE THREAT DUE TO
HIGH FREEZING/WET BULB ZERO VALUES. NAM/SREF SUGGESTING UPWARDS OF
60 TO 70 PERCENT POPS WHILE GFS ONLY HINTING AT 20 TO 30 PERCENT
POPS. WILL GO MIDDLE OF THE ROAD WITH A 50/50 CHANCE WITH PRECIP
POSSIBLY LINGERING INTO EARLY SATURDAY SOUTHERN CWFA. TEMPS AHEAD
OF THE FRONT COULD MAKE A RUN AT 90 DUE TO WARM TONGUE ALOFT AND
COMPRESSIONAL HEATING.
BEYOND THEN...THE FORECAST DOESN`T APPEAR AS CLEAN AS PREVIOUSLY
THOUGHT. THE FRONT ESSENTIALLY STALLS JUST TO OUR SOUTH ACROSS
NORTHERN KANSAS/MISSOURI. GIVEN ITS CLOSE PROXIMITY TO OUR
WESTERN/SOUTHERN AREAS WITH POTENTIAL FOR WEAK IMPULSES TO MOVE
THROUGH THE REGION...ALONG WITH 850MB FRONT REMAINING IN THE AREA...
HAVE DECIDED TO MENTION SLIGHT CHANCE POPS SATURDAY NIGHT THROUGH
SUNDAY...BUT TRIED TO KEEP NORTHEAST CWFA DRY DURING THIS TIME.
FOR THE EXTENDED...BASED MOST OF THE FORECAST ON HPC GUIDANCE
WHICH USED A BLEND OF VARIOUS MODELS AND THEIR ENSEMBLES. WENT DRY
FOR TUESDAY...BUT THEN INCLUDED SMALL POPS FOR WEDNESDAY/THURSDAY
AS A COUPLE OF FRONTS MOVE THROUGH THE REGION.
&&
.AVIATION...
FOR TAF SITES KOMA/KLNK/KOFK THROUGH 22/18Z.
LOW LEVEL CLOUDS AND MVFR CONDITIONS WILL EXIST BRIEFLY EARLY THIS
AFTERNOON DUE TO CONTINUING MOISTURE ADVECTION INTO THE REGION.
LATER THIS AFTERNOON AND EVENING...SHOULD SEE CLOUDS BEGIN TO
DISSIPATE AND VFR CEILINGS AT ALL SITES THROUGH THE REST OF THE DAY
INTO THE EARLY MORNING HOURS. A NEW FRONTAL SYSTEM WILL BEGIN TO
MOVE ACROSS OUR AREA EARLY TOMORROW MORNING WITH THE PROSPECT OF 500
FT CEILINGS AND IFR CONDITIONS AT ALL SITES BY 11Z. BY 13Z...VFR
CONDITIONS ARE EXPECTED TO RETURN AT ALL SITES THROUGH THE END OF
THE PERIOD.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$
.FORECAST...DEWALD
.AVIATION...KURTZ
