SWODY1
SPC AC 181235
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0735 AM CDT TUE SEP 18 2007
VALID 181300Z - 191200Z
..THERE IS A SLGT RISK OF SVR TSTMS FROM THE CENTRAL PLAINS INTO
THE UPPER MS RIVER VALLEY...
..CENTRAL PLAINS INTO THE UPPER MS RIVER VALLEY...
COMPLEX SCENARIO TODAY AS NEUTRAL TO POSITIVELY-TILTED SHORTWAVE
TROUGH CONTINUES TO EJECT ENEWD ACROSS THE CENTRAL/NRN PLAINS...WITH
ASSOCIATED BAND OF MOIST CONVECTION/CLOUDS OVERSPREADING MUCH OF THE
AREA THIS AFTERNOON. SURFACE COLD FRONT EXTENDING FROM N-CENTRAL MN
INTO CENTRAL NEB/ERN CO AT 12Z WILL CONTINUE ESEWD THROUGH THE
PERIOD...WITH 09Z RUC ANALYZING FRONT FROM THE MN ARROWHEAD REGION
INTO S-CENTRAL NEB BY 21Z.
FAIRLY STRONG SSWLY LOW LEVEL FLOW WILL PERSIST AHEAD OF THIS SYSTEM
AND MAINTAIN INFLUX OF LOWER TO MID 60F SURFACE DEW POINTS. DESPITE
THIS...HEATING WILL BE LIMITED DUE TO PERSISTENT AREA OF
PRECIPITATION/THUNDERSTORMS WHICH MODELS DEVELOP STEADILY NEWD AHEAD
OF THE COLD FRONT TODAY. THIS WILL HINDER SURFACE BASED INSTABILITY
ACROSS MUCH OF THE AREA. HOWEVER...MODEST MUCAPE MAY STILL SUPPORT
A FEW STRONGER CORES WITH THIS PREFRONTAL AREA OF THUNDERSTORMS
GIVEN 30-40 KT EFFECTIVE SHEAR UNDER STRONG SWLY MID/UPPER LEVEL
FLOW. SHEAR WILL BE MAXIMIZED ACROSS THE MID MO/UPPER MS RIVER
VALLEYS IN PROXIMITY TO 40-50 KT LLJ AND 60+ KT SWLY H5
WINDS...SUGGESTING A RELATIVE INCREASE IN SEVERE THREAT SHOULD
POCKETS OF HEATING/INSTABILITY DEVELOP.
MORE ROBUST DEVELOPMENT IS MORE LIKELY TO OCCUR NEARER THE COLD
FRONT/SURFACE TROUGH LATER THIS AFTERNOON ALONG WRN PERIPHERY OF
CLOUD SHIELD WHERE HEATING WILL BE STRONGER. RUC AND NAMKF FORECAST
SOUNDINGS INDICATE MLCAPE FROM 1000-1500 J/KG WILL OCCUR ACROSS SRN
AND WRN PARTS OF SLGT RISK AREA BY 21Z...LIKELY SUPPORTING THREAT OF
SEVERE THUNDERSTORMS SPREADING ENEWD INTO THE MID TO LATE EVENING.
FORECAST SOUNDINGS ALSO INDICATE FAVORABLE SHEAR FOR
SUPERCELLS...ALTHOUGH SHEAR VECTORS PARALLELING INITIATING
BOUNDARIES SHOULD FAVOR EVOLUTION INTO SMALL LINES.
.EVANS/BRIGHT.. 09/18/2007
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