SWODY1
SPC AC 231600
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1100 AM CDT SUN SEP 23 2007
VALID 231630Z - 241200Z
..THERE IS A SLGT RISK OF SVR TSTMS LATER THIS AFTERNOON AND
EVENING OVER PORTIONS OF CENTRAL AND NORTHERN PLAINS...
..SYNOPSIS...
UPPER LOW OFF CA COAST LAST FEW DAYS HAS OPENED INTO A TROUGH AND
CURRENTLY ACCELERATING NEWD ACROSS THE GREAT BASIN AS UPSTREAM
SYSTEM DIGS SEWD FROM PAC NW. TROUGH IS PRECEEDED BY STRONG SWLY
FLOW AT ALL LEVELS THAT WILL BE SPREADING EWD INTO NRN/CENTRAL HIGH
PLAINS DURING THE AFTERNOON. IN CONCERT WITH ARRIVAL OF THE COLD
FRONT NOW CROSSING THE NRN/CENTRAL ROCKIES...DEVELOPMENT OF SEVERE
THUNDERSTORMS ARE EXPECTED BY LATER THIS AFTERNOON AS FRONT
ENCOUNTERS PLUME OF MOIST/UNSTABLE AIR AVAILABLE OVER THE PLAINS.
..CENTRAL/NORTHERN PLAINS...
SKIES ARE GENERALLY CLEAR THIS MORNING OVER THE CENTRAL AND NORTHERN
PLAINS...WITH STRONG SOUTHERLY LOW LEVEL WINDS AND SURFACE DEWPOINTS
IN THE LOWER/MID 60S. FULL SUNSHINE WILL HELP TO STEEPEN LOW LEVEL
LAPSE RATES AND DESTABILIZE AIR MASS BY MID AFTERNOON FROM WESTERN
KS INTO ND. FORECAST SOUNDINGS SHOW MLCAPE VALUES FROM 1000-1500
J/KG OVER ERN CO/WRN KS/NEB...INCREASING TO NEAR 2000 J/KG OVER
PORTIONS OF THE EASTERN DAKOTAS. LARGE SCALE FORCING FOR ASCENT IS
EXPECTED TO INCREASE RAPIDLY DURING THE AFTERNOON AS COLD FRONT
SWEEPS EASTWARD INTO PARTS OF WESTERN SD/NEB AND NORTHEAST CO.
CONVERGENCE/LIFT ALONG FRONT WILL HELP TO INITIATE SCATTERED
THUNDERSTORMS. THESE STORMS WILL LIKELY BE RATHER HIGH-BASED AND
FAST-MOVING WITH A THREAT OF HAIL AND GUSTY/DAMAGING WINDS. MODEL
GUIDANCE IS IN GENERAL AGREEMENT THAT PLUME OF HIGHER LOW LEVEL
THETA-E WILL BE RATHER NARROW... CONSTRAINING PRIMARY REGION OF
SEVERE THREAT TO A BELT EXTENDING FROM WESTERN NEB INTO EASTERN ND.
LOW LEVEL AND DEEP LAYER VERTICAL SHEAR VECTORS SHOULD BE FAVORABLE
FOR THE POTENTIAL OF ORGANIZED BOW/LEWP STRUCTURES ALONG THIS ZONE
WITH AN ENHANCED THREAT OF DAMAGING WINDS. STORMS WILL LIKELY
WEAKEN OVER MOST REGIONS BY 03Z...EXCEPT FOR PARTS OF EASTERN ND
WHERE SEVERE POTENTIAL MIGHT CONTINUE AFTER MIDNIGHT.
..ERN MT...
A FEW STRONG STORMS ARE LIKELY BY LATER THIS AFTERNOON AS MID LEVEL
COOLING AND LARGE SCALE ASCENT SPREAD ACROSS ERN MT. WITH
STEEPENING LAPSE RATES AND MLCAPE TO 500 J/KG THUNDERSTORMS SHOULD
DEVELOP EWD FROM HIGHER TERRAIN CENTRAL MT WITH PRIMARY THREAT
MARGINALLY SEVERE HAIL AND GUSTY WINDS.
.HALES/GUYER.. 09/23/2007
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