DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0801 AM CDT WED MAY 12 2004 VALID 121300Z - 131200Z THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 70 NW ANJ 30 WNW MKE 20 W UMN 15 SW TUL 30 NNE OKC 15 NE FSI 20 WNW LTS 20 WSW GAG 10 WNW LBL 15 SSW LAA 30 E COS 35 ENE DEN 40 NW AKO 30 SSW IML 20 S HSI 35 ENE OMA 25 NW MCW 20 NNE ELO. GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 25 WNW DRT 25 N SJT 40 S CDS 55 NNW CDS 40 SSE EHA 50 SSE LHX 40 NW TAD 10 N DRO 15 SSW CNY 20 W ENV 40 S OWY 60 W OWY 20 SSE BNO 10 NNE PDT 35 W PUW 40 SSW 3DU 20 SSW LVM 20 ENE CPR BFF 10 NE LBF 15 NE BUB YKN 15 N BKX 30 E FAR RRT ...CONT... 25 E MSS 20 NE LEB PSM ...CONT... 40 SSE JAX 45 SE CTY ...CONT... 35 NE CRP 20 S LRD. ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER MS VALLEY / GREAT LAKES SWWD INTO KS / ERN CO / OK... ...SYNOPSIS... MAIN UPPER TROUGH NOW OVER THE ROCKIES WILL MOVE VERY SLOWLY EWD THROUGH THIS PERIOD...WHILE SEVERAL WEAKER FEATURES MOVE NEWD ACROSS THE PLAINS IN BELT OF STRONGER SWLY MID-LEVEL FLOW ALONG ERN PERIPHERY OF MAIN TROUGH. A SECOND SHORT-WAVE TROUGH -- WELL AHEAD OF MAIN TROUGH -- NOW EXTENDING FROM ERN KS SWD TO THE TX / LA BORDER WILL CONTINUE MOVING SLOWLY EWD ACROSS THE MID AND LOWER MS VALLEY THROUGH THE PERIOD. AT THE SURFACE...COLD FRONT ASSOCIATED WITH MAIN UPPER TROUGH NOW EXTENDS FROM LOW PRESSURE OVER MN SWWD INTO OK / NRN TX PANHANDLES AND THEN WWD INTO SRN CO. THIS FRONT IS FORECAST TO MOVE STEADILY EWD ACROSS THE GREAT LAKES...WHILE SEWD SURGE INTO THE SRN PLAINS SLOWS THROUGH THE MORNING. BY AFTERNOON...SURFACE LOW IS FORECAST TO DEEPEN ALONG BOUNDARY ACROSS SERN CO. THIS WILL LIKELY ALLOW BOUNDARY TO RETREAT NWD INTO WRN KS / ERN CO THIS AFTERNOON. BY LATE IN THE PERIOD...BOUNDARY SHOULD CONTINUE ITS SWD PUSH ACROSS THE TX / OK PANHANDLE REGION. ...UPPER MS VALLEY / WRN GREAT LAKES SWWD INTO KS / OK / ERN CO... MID TO UPPER 60S DEWPOINTS EXIST AHEAD OF ADVANCING COLD FRONT ATTM...WHILE CAPPED LOW-LEVEL AIRMASS IS RESULTING IN WIDESPREAD LOW CLOUDINESS OVER THE CENTRAL AND SRN PLAINS. HOWEVER...DAYTIME HEATING / MIXING SHOULD EVENTUALLY ALLOW CLOUDS TO BREAK UP AND HEATING TO COMMENCE...WITH 2000 TO 3000 J/KG MEAN-LAYER CAPE EXPECTED BY AFTERNOON. STORMS ARE FORECAST TO INITIATE INVOF COLD FRONT -- INITIALLY ACROSS WRN KS OR WWD INTO CO IN SELY UPSLOPE FLOW REGIME. ISOLATED STORMS ARE ALSO FORECAST TO DEVELOP SWD ALONG DRYLINE ACROSS OK / TX. STRONGEST INSTABILITY / SHEAR COMBINATION IS FORECAST ACROSS KS...WHERE 40 TO 50 KT 0-6 KM SHEAR IS EXPECTED. STORMS SHOULD THEREFORE BECOME RAPIDLY SUPERCELLULAR...WITH VERY LARGE HAIL AND DAMAGING WINDS EXPECTED. AN ISOLATED TORNADO WILL ALSO BE POSSIBLE...PARTICULARLY FROM ERN CO INTO WRN KS WHERE LOW-LEVEL SHEAR WILL BE MOST FAVORABLE. FURTHER SWD ALONG DRYLINE...SHEAR IS FORECAST TO BE WEAKER -- BUT STILL STRONG ENOUGH FOR MULTICELLS / WEAK UPDRAFT ROTATION. THIS COMBINED WITH STRONG INSTABILITY SUPPORTS A THREAT FOR LARGE HAIL AND LOCALLY DAMAGING WINDS. OVERNIGHT...STORMS WILL LIKELY INCREASE IN COVERAGE AS LOW-LEVEL JET DEVELOPS. SEVERE THREAT SHOULD PERSIST THROUGH MUCH OF THE NIGHT AS ONE OR MORE MCSS LIKELY EVOLVE OVER KS / OK. ...UPPER MS VALLEY INTO THE WRN GREAT LAKES REGION... SHOWERS AND STORMS ARE ONGOING ATTM ALONG COLD FRONT FROM MN SSWWD INTO NERN KS. LOW 60S DEWPOINTS COMBINED WITH DAYTIME HEATING SHOULD ALLOW MARGINAL AIRMASS DESTABILIZATION TO OCCUR. AS A RESULT...EXPECT SOME INCREASE IN STORM INTENSITY BY AFTERNOON ALONG / AHEAD OF FRONT. IN ADDITION TO LIMITED INSTABILITY...STRONGER DEEP-LAYER WIND FIELD IS FORECAST TO REMAIN ON THE COLD SIDE OF SURFACE BOUNDARY. HOWEVER...INSTABILITY / SHEAR IN THE IMMEDIATE VICINITY OF COLD FRONT WILL LIKELY SUPPORT LOCALLY DAMAGING WINDS AND SOME HAIL WITH A FEW OF THE STRONGER STORMS. ALTHOUGH CONVECTION SHOULD SPREAD EWD INTO THE GREAT LAKES REGION OVERNIGHT...SEVERE THREAT SHOULD SLOWLY DECREASE WITH THE LOSS OF DAYTIME HEATING. ...MID AND LOWER MS VALLEY REGION... MOIST LOW-LEVEL AIRMASS IS EVIDENT THIS MORNING ACROSS THE MIDDLE AND LOWER MS VALLEY REGION AHEAD OF WEAK UPPER SHORT-WAVE TROUGH. STORM CLUSTER CONTINUES ACROSS AR / LA / WRN MS WITHIN MESOSCALE CIRCULATION NOW OVER FAR SERN AR ATTM. AS THIS FEATURE AND SECOND / WEAKER CIRCULATION EVIDENT OVER W CENTRAL MO ATTM MOVE EWD THROUGH THIS AFTERNOON...AND INCREASE IN STORMS IS EXPECTED ALTHOUGH INTENSITY IS FORECAST TO BE SOMEWHAT LIMITED DUE TO ONLY MARGINAL INSTABILITY. NONETHELESS...COMBINATION OF MODERATE / 20 TO 30 KT / WINDS THROUGH A DEEP LAYER AND PRESENCE OF MESOSCALE CIRCULATION CENTERS MAY ALLOW SOME STORM ORGANIZATION / PERSISTENCE. ALONG WITH A THREAT FOR A LOCALLY DAMAGING GUST OR TWO...AN ISOLATED TORNADO WILL ALSO BE POSSIBLE GIVEN FAIR DEGREE OF LOW-LEVEL SHEAR AND MOIST LOW-LEVEL AIRMASS. DIURNAL WEAKENING OF CONVECTION THIS EVENING SHOULD ALLOW ANY SEVERE THREAT TO DIMINISH. ..GOSS / TAYLOR.. 05/12/2004