SWODY1
SPC AC 291220
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0720 AM CDT THU MAY 29 2008
VALID 291300Z - 301200Z
...THERE IS A HIGH RISK OF SVR TSTMS THIS AFTERNOON AND EVENING OVER
PORTIONS OF EASTERN NEB...WESTERN IA...AND EXTREME SOUTHEAST SD...
...THERE IS A MDT RISK OF SVR TSTMS OVER PARTS OF NORTHERN
KS...CENTRAL NEB...CENTRAL IA...SOUTHEAST SD...AND SOUTHWEST MN...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE TX PANHANDLE TO
SOUTHERN WI...
...REGIONAL OUTBREAK OF SEVERE THUNDERSTORMS AND TORNADOES EXPECTED
TODAY OVER PARTS OF NEB/IA/SD...
MORNING WATER VAPOR IMAGERY SHOWS A BROAD UPPER TROUGH OVER THE
WESTERN STATES...WITH A BAND OF MODERATELY STRONG SOUTHWESTERLY MID
LEVEL WINDS EXTENDING FROM THE FOUR-CORNERS INTO THE CENTRAL PLAINS.
A WELL-DEFINED SHORTWAVE TROUGH IS NOTED OVER WESTERN CO. THIS
FEATURE WILL EMERGE INTO THE CENTRAL HIGH PLAINS BY EARLY AFTERNOON
AND AID IN THE DEVELOPMENT OF INTENSE CONVECTION ACROSS PARTS OF
KS/NEB/SD/IA. STRONG SOUTHERLY LOW LEVEL WINDS ACROSS THE
SOUTHERN/CENTRAL PLAINS ARE TRANSPORTING GULF MOISTURE RAPIDLY
NORTHWARD AT AND ABOVE THE SURFACE. DEWPOINTS APPEAR LIKELY TO
CLIMB INTO THE MID-UPPER 60S OVER EASTERN NEB/WESTERN IA BY LATE
AFTERNOON. STRONG DAYTIME HEATING AND VERY STEEP MID LEVEL LAPSE
RATES WILL COMBINE TO YIELD MLCAPE VALUES OF 2500-3500 J/KG.
THUNDERSTORMS ARE EXPECTED TO INITIATE FIRST ALONG THE SURFACE
DRYLINE OVER WESTERN NEB/KS BY MID AFTERNOON. THESE STORMS WILL BE
RATHER HIGH-BASED...BUT WILL LIKELY BE SUPERCELLULAR DUE TO STRONG
DEEP LAYER VERTICAL SHEAR. MORE STORMS ARE EXPECTED TO DEVELOP OVER
THE WARM SECTOR IN EASTERN NEB/WESTERN IA DURING THE LATE AFTERNOON
AND EARLY EVENING IN REGION OF RELATIVELY WEAK CINH AND STRONG CAPE.
THESE STORMS WILL BE IN AN ENVIRONMENT OF LOWER LCLS...STRONGER LOW
LEVEL VERTICAL SHEAR/HELICITY...AND MORE SUBTLE FORCING. THESE
FACTORS ARE EXPECTED TO RESULT IN A SEVERAL HOUR PERIOD OF DISCRETE
SUPERCELLS CAPABLE OF VERY LARGE HAIL AND POTENTIALLY STRONG
TORNADOES. MODELS DIFFER ON PLACEMENT OF SURFACE WARM FRONT AND
MOST LIKELY CORRIDOR OF SIG TORNADO THREAT. HOWEVER...IT APPEARS AT
THIS TIME TO EXTEND FROM ONL/GRI THROUGH THE SUX AREA INTO WESTERN
IA. LOW LEVEL WINDS AND VERTICAL SHEAR CONTINUE TO STRENGTHEN AFTER
DARK IN THIS AREA WITH A SUSTAINED THREAT OF STRONG TORNADOES.
EVENTUALLY...ACTIVITY THAT DEVELOPED ALONG THE DRYLINE WILL SURGE
INTO THIS AREA AND LIKELY ORGANIZE CONVECTION INTO A FAST-MOVING
MCS. AN ENHANCED THREAT OF WIDESPREAD DAMAGING WINDS IS EXPECTED TO
DEVELOP ACROSS WESTERN/CENTRAL IA DURING THE EVENING.
THE THREAT OF SIGNIFICANT SEVERE WEATHER APPEARS TO DIMINISH RAPIDLY
SOUTH OF I-70 DUE TO WARMER MID LEVEL TEMPERATURES AND WEAKER DEEP
LAYER SHEAR. NEVERTHELESS...A FEW ISOLATED SEVERE STORMS WILL BE
POSSIBLE ALONG SURFACE DRYLINE ACROSS THE OK/TX PANHANDLES INTO
PARTS OF EASTERN NM,
..HART/JEWELL.. 05/29/2008
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