FXUS63 KOAX 230756
AFDOAX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE OMAHA/VALLEY NE
255 AM CDT TUE AUG 23 2011
...HIGH HEAT INDEXES TODAY A CONCERN WITH THUNDERSTORM CHANCES
RETURNING THURSDAY NIGHT AND BEYOND...
.DISCUSSION...
AN UPPER LEVEL DISTURBANCE IS CURRENTLY CROSSING THE EASTERN DAKOTAS
INTO MINNESOTA WITH AN MCS MOVING SOUTHEAST FROM NORTHERN IOWA.
BESIDES A TRAILING OUTFLOW BOUNDARY REACHING INTO FAR NORTHERN
COUNTIES...CONVECTIVE DEVELOPMENT APPEARS UNLIKELY THE NEXT FEW
HOURS.
NO THUNDERSTORMS FORECAST ACROSS EASTERN NEBRASKA AND SOUTHWEST IOWA
THROUGH TONIGHT. GENERAL SUBSIDENCE WILL RULE THE AREA WITH
CONSIDERABLE DRYING INDICATED IN THE H85 TO H7 LAYER. IN THE LOWER
BOUNDARY LAYER...MOISTURE WILL POOL AND REMAIN HIGH THROUGH THIS
EVENING AS A SURFACE TROUGH SLOWLY ADVANCES EASTWARD FROM CENTRAL
NEBRASKA TODAY. DEWPOINTS...PARTICULARLY IN THE MISSOURI VALLEY AND
SOUTHWEST IOWA WILL REACH INTO THE UPPER 70S. COMBINED WITH HIGHS OF
92 TO 95...THIS WILL BRING HIGH HEAT INDICES OF 100 TO 105 WITH NEAR
107 POSSIBLE ACROSS SOUTHEASTERN COUNTIES.
A WEAK COLD FRONT WILL MOVE IN LATE TONIGHT AND WILL EXIT SOUTHERN
COUNTIES BY 18Z WEDNESDAY. THIS WILL BE A DRY FRONT WITH HIGHS
DROPPING BACK MAINLY INTO THE UPPER 80S. SURFACE HIGH PRESSURE WILL
BUILD IN...GRADUALLY WORKING TOWARD THE LOWER GREAT LAKES BY
THURSDAY EVENING. HIGHS THURSDAY WILL BE A BIT COOLER FROM 83 TO 87
WITH A WEAK SOUTHERLY FLOW RETURNING.
THE GFS HAS BEEN CONSISTENT WITH INDICATING CONVECTION POTENTIAL IN
WARM AIR ADVECTION THURSDAY NIGHT. HAVE INTRODUCED A SLIGHT
CHANCE...AS COVERAGE...IF IT DEVELOPS MAY ONLY BE ISOLATED.
FOR FRIDAY AND SATURDAY...
WILL CARRY A SLIGHT CHANCE FRIDAY FOR NORTHERN ZONES WITH CHANCE
POPS KEPT FRIDAY NIGHT WITH BEST CHANCES ACROSS NORTHERN ZONES NEAR
AND NORTH OF THE FRONT.
WILL NOT MAKE ANY MAJOR CHANGES TO THE FORECAST FORECAST BEYOND
FRIDAY WITH MAINLY A SLIGHT CHANCE GOING THROUGH THE WEEKEND WITH
NORTHWEST FLOW ALOFT AGAIN BECOMING ESTABLISHED.
KAR
&&
.AVIATION...
FOR THE 06Z TAFS...
POTENT UPPER IMPULSE WILL CONTINUE TO PUSH EAST INTO THE UPPER
MIDWEST...SUPPORTING A SLOW MOVING SFC TROUGH INTO THE REGION. ALL
CONVECTION WILL REMAIN WELL NE OF THE FA GIVEN LOCATION OF LARGE
SCALE ASCENT AND THE POSITION OF THE LLJ NOSE AND ASSOCIATED THETA-E
ADV. LL PRESSURE FALLS AHEAD OF THIS IMPULSE WILL CONTINUE TO
SUPPORT TURBULENT MIX DOWN ALLOWING SFC WINDS TO STAY MIXED THROUGH
AM AT MOST PLACES NORTH OF I80...SAVE SOME PROTECTED VALLEY AREAS.
HENCE...VFR CONDITIONS EXPECTED AT MOST TAF SITES THROUGH MID
MORNING...WITH A POSSIBLE PERIOD OF MVFR VIS AT LNK WHERE DECOUPLING
POTENTIAL WILL BE THE HIGHEST. DEEP MIXING IN A HIGHLY CAPPED
ATMOSPHERE...WILL SUPPORT VFR CONDITIONS AT ALL LOCATIONS THROUGH
THE REMAINDER OF THE PERIOD WITH POSSIBLY SOME PASSING CIRRUS AND
MID CLOUD.
JC
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
IA...NONE.
&&
$$