DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0102 AM CDT WED MAY 19 2004 VALID 191200Z - 201200Z THERE IS A MDT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 50 WSW YKN 45 N ATY 20 NW AXN 30 NW RWF 25 NNW FRM 10 SSE MCW 15 SW ALO 35 SW OTM 40 NNE FNB 20 SW LNK 20 NNE GRI 50 WSW YKN. THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 40 NE ORF 15 W BLF 25 NE BWG 10 ESE MDH JEF 25 ENE MKC 20 NNE MHK 40 SSW EAR 10 SW LBF 20 ENE PHP 40 NE Y22 50 NNW MOT ...CONT... 35 NNW TVC GRR 45 NNE FWA 35 SSE FDY 20 SSE AOO 25 S JFK. GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 15 SE BPT 15 NNE ESF 35 S GWO 40 N TUP 15 NNE MKL 20 ESE POF 20 NE JLN 40 SSW EMP 20 WNW HUT 35 WNW GAG 50 SE LBB 20 ESE P07 ...CONT... 40 S DMN 45 SE GNT 20 E RTN 35 SSE LIC 35 WSW AKO 10 WNW FCL 15 NNE SLC 60 NW ELY 45 SSE NFL 30 WSW TVL 30 NW SAC 50 SW MHS 35 NE MFR 35 N SEA 20 NE BLI. GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 40 NNW SYR 10 NNE ELM 15 S AVP 15 S BDR. ...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING ACROSS PORTIONS OF ERN NEB/ERN SD/SWRN MN AND MUCH OF CENTRAL/WRN IA... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE NRN/CENTRAL PLAINS EWD TO THE WRN GREAT LAKES REGION...AND MID MS/OH VALLEYS TO MID ATLANTIC REGION... ...ACTIVE SEVERE WEATHER DAY IS EXPECTED ACROSS PORTIONS OF THE ERN PLAINS INTO THE UPPER MS VALLEY... ...SYNOPSIS... NERN PACIFIC UPPER RIDGE WILL CONTINUE TO BUILD NWD TODAY ACROSS ALASKA...RESULTING IN DOWNSTREAM PACIFIC NW TROUGH TO RETROGRADE SWWD ALONG THE U.S. WEST COAST AS HEIGHTS RISE ACROSS THE CENTRAL/ SRN PLAINS. SHORT WAVE TROUGH...NOW OVER CENTRAL MT...WILL MOVE ENEWD ACROSS ND/FAR SRN CANADA AS AN OPEN...POSITIVELY TILTED TROUGH...REACHING CENTRAL ONTARIO/UPPER GREAT LAKES BY 12Z THURSDAY. AN INCREASE IN WLY MID-LEVEL FLOW IS EXPECTED ACROSS THE NORTH CENTRAL STATES THIS FORECAST PERIOD AS THE HEIGHT GRADIENT TIGHTENS BETWEEN THE BUILDING RIDGE OVER THE CENTRAL/SRN PLAINS AND A TROUGH MOVING SWD ACROSS THE CENTRAL CANADIAN PROVINCES. AT THE SURFACE... A LEE LOW OVER THE WRN DAKOTAS WILL DEEPEN AS IT MOVES ENEWD ACROSS NRN MN...AND THEN ACCELERATE TOWARD JAMES BAY BY 12Z THURSDAY. SURFACE BOUNDARY INITIALLY OVER THE LOWER MO VALLEY WILL MOVE NEWD AS A WARM FRONT ACROSS THE UPPER MS VALLEY REACHING MI/OH BY THE END OF THE PERIOD. THIS BOUNDARY COMBINED WITH A COLD FRONT MOVING EWD ACROSS THE NRN PLAINS TO THE UPPER MS VALLEY BY THE END OF THE PERIOD WILL BE THE FOCI FOR AN ACTIVE SEVERE WEATHER DAY... PARTICULARLY IN THE PLAINS/UPPER MS VALLEY. IN THE EAST...UPPER TROUGH INITIALLY OVER THE NERN STATES TO UPPER OH VALLEY WILL MOVE EWD AND BE REPLACED BY SHORT WAVE RIDGING. ...LOWER MO/UPPER MS VALLEYS EWD TO THE GREAT LAKES REGION... THUNDERSTORMS...SOME SEVERE...MAY BE ONGOING AT THE START OF THE PERIOD ACROSS NRN SD INTO ND WITHIN MOIST/WAA REGIME TO THE EAST OF THE SURFACE LOW...SUPPORTING ISOLATED HAIL. NOCTURNAL SLY LLJ OVER THE DAKOTAS...AND SECOND SLY LLJ OVER THE SRN PLAINS WILL MAINTAIN THEIR INTENSITY AS THEY TRANSLATE EWD THROUGH THE DAY. THIS SLY LOW-LEVEL FLOW WILL ADVECT MOISTURE NWD AS THE WARM FRONT RETREATS NNEWD. AXIS OF SURFACE DEWPOINTS IN THE 60S WILL EXTEND ACROSS THE ERN DAKOTAS/WRN MN BY MID-LATE AFTERNOON WITH VALUES IN THE LOWER 70S ACROSS ERN NEB/WRN IA. SUFFICIENT MOISTURE /850 MB DEWPOINTS 16-18C BY 00Z ACROSS ERN NEB/...SURFACE HEATING AND STEEP LAPSE RATES WILL RESULT IN A VERY UNSTABLE AIR MASS FROM ERN SD/ERN NEB INTO IA WITH EXTREME INSTABILITY /MLCAPE AOA 4000 J/KG/ OVER ERN NEB/FAR WRN IA. NNELY RETURN OF MOISTURE WILL ALSO SUPPORT A MODERATELY UNSTABLE AIR MASS NWD ACROSS NWRN MN AND EWD INTO WI THIS EVENING AND NRN IL OVERNIGHT. INCREASING MID-LEVEL FLOW WITH THE SHORT WAVE TROUGH MOVING ACROSS THE DAKOTAS/NRN MN WILL RESULT IN STRONG WLY ORIENTED DEEP LAYER SHEAR VECTORS OF 45-60 KT TO SUPPORT WIDESPREAD SEVERE STORMS... ESPECIALLY WITHIN THE MODERATE RISK AREA BY LATE AFTERNOON. MODELS SUGGEST ONGOING STORMS OVER THE DAKOTAS THIS MORNING WILL REDEVELOP AND/OR INTENSIFY AS THEY MOVE EWD ACROSS NRN/CENTRAL MN THIS AFTERNOON. ADDITIONAL STORMS WILL LIKELY DEVELOP SWD ALONG THE WARM FRONT FROM ERN SD/NERN NEB/WRN IA...WHERE THE AIR MASS WILL BE EXTREMELY UNSTABLE AND SUPPORT POTENTIALLY LONG-LIVED SUPERCELLS/SUPERCELL CLUSTERS WITH TORNADOES...LARGE HAIL AND DAMAGING WINDS. THE GREATEST POTENTIAL FOR SIGNIFICANT TORNADOES SHOULD BE ACROSS ERN NEB/FAR SERN SD/FAR SWRN MN AND WRN/SRN IA WHERE SHEAR VECTORS FAVOR STORMS REMAINING ALONG THE WARM FRONT. THIS ACTIVITY WILL MOVE EWD ACROSS SRN MN/IA THIS EVENING/ OVERNIGHT IN THE FORM OF ONE OR TWO SEVERE MCS/S WITH THE THREAT TRANSITIONING INTO PRIMARILY A WIND THREAT AS THESE COMPLEXES MOVE INTO WI/ERN IA/NRN IL. ACTIVITY MAY REACH FAR WRN LOWER MI BY 12Z THURSDAY. ADDITIONAL SEVERE STORMS WILL ALSO LIKELY DEVELOP ALONG THE COLD FRONT AS IT MOVES EWD ACROSS THE ERN DAKOTAS/ERN NEB AND UPPER MS VALLEY AFTER 00Z. ...MID ATLANTIC REGION WWD TO THE MIDWEST/MID MS VALLEY... SURFACE BAROCLINIC ZONE WILL SAG SWD ACROSS THE DELMARVA REGION WWD TO THE OH/MID MS VALLEYS...WITH ABUNDANT MOISTURE REMAINING ALONG AND SOUTH OF THIS BOUNDARY. ADDITIONAL MOISTURE SHOULD ADVECT NEWD ALONG TROUGH IN LEE OF THE SRN/CENTRAL APPALACHIANS INTO THE DELMARVA REGION. LONG-LIVED MCV/SHORT WAVE TROUGH...CURRENTLY LOCATED ACROSS ERN IND/WRN OH...WILL MOVE ESEWD ACROSS THE MID ATLANTIC REGION TODAY ENHANCING WIND FIELDS/DEEP LAYER SHEAR AND LARGE SCALE ASCENT FOR THUNDERSTORMS ALONG THE SURFACE BOUNDARY WITHIN MARGINALLY TO MODERATELY UNSTABLE AIR MASS. DEEP WLY FLOW WITH 30-35 KT OF DEEP LAYER SHEAR WILL SUPPORT LINES/BOW SEGMENTS WITH THIS ACTIVITY ALONG WITH HAIL. FARTHER WEST ALONG THE QUASI-STATIONARY BOUNDARY...SCATTERED STORMS SHOULD DEVELOP FROM SRN OH WWD TO THE MID MS VALLEY...WITH A CLUSTER OF STORMS POTENTIALLY ONGOING AT THE START OF THE PERIOD OVER THE NRN HALF OF MO INTO WRN IL. DESPITE WEAK LAPSE RATES...A MOIST AIR MASS WITH SURFACE DEWPOINTS IN THE MID-UPPER 60S WILL CONTRIBUTE TO MLCAPE VALUES RANGING FROM 500-1000 J/KG ALONG THE BAROCLINIC ZONE. THIS COMBINED WITH WEAK DEEP LAYER SHEAR VALUES WILL RESULT IN PULSE-TYPE MULTI-CELL STORMS WITH STRONG WIND GUSTS AND HAIL THE MAIN THREATS THROUGH THE DAY. SEVERE ACTIVITY IS EXPECTED TO WEAKEN DURING THE EVENING WITH THE LOSS OF DAY TIME HEATING. ..PETERS/TAYLOR.. 05/19/2004