DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1115 AM CDT WED APR 21 2004 VALID 211630Z - 221200Z THERE IS A MDT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM HRO 35 NW LIT HOT 25 N TXK PRX ADM GAG 40 WSW P28 BVO UMN HRO. THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 40 NNE ART MSV DOV DCA MGW CRW 35 SW HSV MLU GGG DAL 45 SE SPS LBL 40 E LAA 50 SE GLD ICT JEF SLO HUF FWA 15 ESE APN. GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 40 ESE EWN 15 ESE RWI 35 NE LYH 15 W SSU 10 ESE RMG 20 WNW LUL 25 WNW HOU 45 NW NIR 35 SSE JCT 40 NNW MWL 15 ESE LTS 35 WNW RTN FMN 40 WNW 4HV 35 NE U31 55 N SVE 30 S MFR 50 NNW 4BK ...CONT... 65 NNE ISN 45 W BIS MBG 50 WNW RWF 20 W FRM 25 NW FNB 25 S FNB MKC ALN 25 W MTO 20 SSE MTW 20 SE ANJ. ...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON AND TONIGHT OVER MUCH OF OK...WESTERN AR...AND SOUTHWEST MO... ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SOUTHERN PLAINS ACROSS THE TN/OH VALLEYS INTO PARTS OF PA/NY... ...SIGNIFICANT SEVERE WEATHER EPISODE LIKELY TO DEVELOP THIS AFTERNOON AND TONIGHT ACROSS PARTS OF OK/AR... MORNING WATER VAPOR IMAGERY SHOWS A LARGE TROUGH OVER MUCH OF THE UNITED STATES TODAY...WITH A SERIES OF SHORTWAVE TROUGHS MOVING QUICKLY WEST TO EAST ACROSS THE CENTRAL PLAINS INTO THE OH VALLEY. MODEL GUIDANCE SHOWS ONE FEATURE CURRENTLY OVER WEST TX...WHICH WILL AMPLIFY AND ROTATE INTO EASTERN OK BY EVENING. THE AIRMASS OVER THIS REGION IS MORE MOIST AT THE SURFACE THAN YESTERDAY WITH WIDESPREAD LOW 60S DEWPOINTS IN PLACE. ALSO...MID LEVEL LAPSE RATES ARE STEEPER AND 500MB TEMPERATURES ARE COOLER...INDICATIVE OF THE MODERATE-STRONG INSTABILITY THAT WILL DEVELOP BY MID-LATE AFTERNOON. POCKETS OF LOW CLOUDS SHOULD CONTINUE TO DIMINISH...RESULTING IN A RATHER LARGE AREA OF UNCAPPED 2000-3000 J/KG MLCAPE. CONVERGENCE ALONG WEAK/SUBTLE SURFACE BOUNDARIES ACROSS NORTHERN OK IS EXPECTED TO RESULT IN EXPLOSIVE THUNDERSTORM DEVELOPMENT BY MID AFTERNOON...SPREADING SOUTHEASTWARD INTO EASTERN OK BY EARLY EVENING. CONVECTIVE MODE THROUGHOUT THIS REGION WILL LIKELY BE SUPERCELLULAR DUE TO STRONG DEEP LAYER VERTICAL SHEAR. VERY LARGE HAIL WILL BE LIKELY WITH STRONGEST STORMS. GREATEST TORNADO THREAT APPEARS TO EXIST NORTH OF OLD OUTFLOW BOUNDARY WHICH WILL LIKELY EXTEND FROM SOUTH OF END EASTWARD TOWARD FSM/MLC WHERE BACKED LOW LEVEL WINDS WILL BE ENHANCED. ALSO...STRONGER SOUTHERLY LOW LEVEL WINDS WILL DEVELOP BY LATE AFTERNOON OVER SOUTHEASTERN OK...PROVIDING FAVORABLE LOW LEVEL SHEAR PARAMETERS FOR POTENTIALLY TORNADIC SUPERCELLS. DAMAGING TORNADOES ARE POSSIBLE IN BOTH OF THESE AREAS. STORMS WILL LIKELY MAINTAIN INTENSITY THROUGH THE EVENING AS THEY MOVE/DEVELOP EASTWARD INTO WESTERN AR AND SOUTHWEST MO...WITH AN INCREASING THREAT OF DAMAGING WINDS. ...SOUTHWEST KS... SEVERE STORMS OVER OK WILL LIKELY DEVELOP WEST-NORTHWESTWARD INTO PARTS OF SOUTHWEST KS BY EVENING. FULL SUNSHINE TODAY WILL RESULT IN VERY STEEP LOW LEVEL LAPSE RATES AND AID IN THE DEVELOPMENT OF AT LEAST MARGINAL INSTABILITY /MLCAPE VALUES AROUND 1000 J/KG/. THIS ACTIVITY WILL LIKELY POSE A RISK OF LARGE HAIL THROUGH THE EVENING BEFORE WEAKENING. ...IN/OH/MI... BROAD PLUME OF SOUTHWEST LOW LEVEL WINDS HAVE MAINTAINED A RELATIVELY MOIST/MARGINALLY UNSTABLE AIRMASS FROM SOUTHERN IND INTO EASTERN LOWER MI. ALTHOUGH MUCH OF THIS AREA WILL HAVE ONLY LIMITED DIURNAL HEATING DUE TO CLOUDS...POTENTIAL EXISTS FOR ISOLATED THUNDERSTORM DEVELOPMENT BY EARLY AFTERNOON. STRONG WINDS ALOFT SUGGEST A RISK OF DAMAGING WINDS IN STRONGER CELLS. ...MS/AL/TN/KY... BAND OF SHOWERS/THUNDERSTORMS CURRENTLY EXTENDS FROM NORTHWEST MS INTO CENTRAL KY. AIRMASS AHEAD OF THIS ACTIVITY WILL DESTABILIZE BY AFTERNOON WITH POCKETS OF MUCAPE OVER 1500 J/KG...AND SUFFICIENT VERTICAL SHEAR FOR THUNDERSTORM ORGANIZATION. THESE STORMS MAY RE-INTENSIFY BY LATE AFTERNOON...WITH THE POTENTIAL FOR LARGE HAIL AND DAMAGING WINDS IN STRONGER CELLS. ...NY/PA/MD/VA... AIRMASS OVER THE DELMARVA REGION INTO WESTERN NY WILL DESTABILIZE RAPIDLY TODAY DUE TO FULL SUNSHINE AND SURFACE DEWPOINTS IN THE 50S. APPROACHING SHORTWAVE TROUGH AND TAIL END OF STRONGER SOUTHERLY LOW LEVEL WINDS SHOULD AID IN THE DEVELOPMENT OF SCATTERED THUNDERSTORMS BY MID/LATE AFTERNOON. FORECAST SOUNDINGS IN THIS REGION SHOW STRONG LOW LEVEL VEERING WINDS WITH HEIGHT AND SUFFICIENT CAPE FOR THE POSSIBILITY OF SUPERCELLS. ACTIVITY IS EXPECTED TO SPREAD NORTHEASTWARD ACROSS NY/PA DURING THE EVENING AND SLOWLY WEAKEN. ..HART/BANACOS.. 04/21/2004