SWODY1
SPC AC 231237
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0737 AM CDT SUN SEP 23 2007
VALID 231300Z - 241200Z
..THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING OVER
PARTS OF THE CENTRAL AND NORTHERN PLAINS...
MORNING SATELLITE IMAGERY LOOPS SHOW A HIGH-AMPLITUDE LARGE SCALE
TROUGH OVER NV/CA...WITH STRONG MID/HIGH LEVEL JET EXTENDING ALONG
AN AXIS FROM AZ INTO WY/MT. THE LARGE SCALE TROUGH IS FORECAST TO
BECOME MORE PROGRESSIVE AND LIFT NORTHEASTWARD THROUGH THE FORECAST
PERIOD WITH JET AXIS SHIFTING EASTWARD INTO THE CENTRAL/NORTHERN
PLAINS. MEANWHILE...STRONG PACIFIC COLD FRONT WILL SURGE EASTWARD
INTO THE PLAINS PROVIDING THE FOCUS FOR STRONG/SEVERE STORMS THIS
AFTERNOON AND EVENING.
..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 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 OF 500-1000 J/KG
OVER KS/CO/NEB...INCREASING TO 1000-1500 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.
..EASTERN MT...
LEFT EXIT REGION OF MID/UPPER LEVEL JET IS FORECAST TO AFFECT PARTS
OF EASTERN MT THIS AFTERNOON AND EVENING. MODEL GUIDANCE SUGGESTS
THE LIKELIHOOD OF LOW LEVEL CYCLOGENESIS AND STRONG FORCING FOR
UPWARD MOTION OVER THIS AREA. FORECAST SOUNDINGS ALSO SUGGEST THE
PRESENCE OF AT LEAST MARGINAL INSTABILITY DUE TO COOL TEMPERATURES
ALOFT AND STEEP MID LEVEL LAPSE RATES. IF THUNDERSTORMS CAN DEVELOP
IN THIS SMALL AREA...THEY WILL BE CAPABLE OF LOCALLY GUSTY WINDS AND
HAIL. OVERALL THREAT DOES NOT APPEAR TO WARRANT A SLIGHT RISK AT
THIS TIME.
.HART/GRAMS.. 09/23/2007
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