DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0107 AM CDT WED APR 21 2004 VALID 211200Z - 221200Z THERE IS A MDT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 30 NE DUA 45 NNE ADM 25 NNE OKC 25 WSW PNC 25 N PNC 35 NW BVO 35 NE BVO 20 WSW UMN 20 SSE HRO 45 NW LIT 10 S HOT 35 NNE TXK 40 ENE PRX 30 NE DUA. THERE IS A SLGT RISK OF SVR TSTMS TO THE RIGHT OF A LINE FROM 50 NNE BUF 25 NNE PIT 30 SW CRW 45 ESE LOZ 40 WNW CHA 15 ENE GWO 30 SSE GLH 40 SSW ELD 30 NNW GGG 30 NE DAL 25 ENE SPS CSM 15 NE GAG 30 SE DDC 35 S RSL 20 ESE SLN 40 E EMP 50 NNE JLN 35 ENE SGF 50 ESE TBN 40 WNW MDH 25 W HUF 40 WSW FWA 25 E APN. GEN TSTMS ARE FCST TO THE RIGHT OF A LINE FROM 15 NNW HSE 35 NE DAN 35 ENE TRI 45 ENE HSV 20 ESE CBM 20 NNE JAN 45 SSE LFK 20 SE NIR 45 W NIR 35 NNE COT 20 ESE BWD 40 SW SPS 10 NE CDS 40 NNW TCC 30 WNW 4BL 50 NE ELY 10 NE 4LW 40 ESE EUG 45 SSE AST 10 NE SEA 4OM 15 E CTB 25 WNW OLF 40 NNW BIS 35 NNW ABR 40 SSW OTG 45 SW FOD 20 E DSM 20 WNW CID 20 ENE AUW 45 ENE MQT. ...THERE IS A MDT RISK OF SVR TSTMS ACROSS NCNTRL OK...ERN OK...WRN AR...FAR SW MO AND FAR SRN KS... ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF KS...OK...NE TX...AR...SRN MO...FAR NRN LA...NRN MS...TN...SRN IL...IND...KY...OH...ERN LOWER MI...FAR WRN WV...FAR WRN TN AND FAR WRN NY... ...SRN PLAINS/CNTRL PLAINS/OZARKS... A WELL-DEFINED MOIST AXIS CURRENTLY EXISTS ACROSS ERN AND NRN OK WHERE LOWER TO MID 60S F SFC DEWPOINTS ARE IN PLACE. A WELL-DEFINED SHORTWAVE TROUGH IS LOCATED ACROSS THE TX PANHANDLE AND THIS SYSTEM WILL MOVE EWD TODAY LIKELY RESULTING IN A WIDESPREAD SEVERE WEATHER EVENT. WLY FLOW ALOFT WILL TAKE RESIDUAL CLOUD COVER FROM YESTERDAYS CONVECTION EWD INTO THE LOWER MS VALLEY THIS MORNING. THIS WILL LEAVE MOSTLY CLEAR SKIES ACROSS THE SRN AND CNTRL PLAINS FOR STRONG SFC HEATING THIS AFTERNOON. FOR THIS REASON...BELIEVE THE MODELS ARE UNDERESTIMATING THE AMOUNT OF INSTABILITY ACROSS OK AND NE TX THIS AFTERNOON. FORECAST SFC TEMPS IN THE MID 70S F SHOULD YIELD MODERATE INSTABILITY WITH 2000 TO 2500 J/KG ACROSS THE MODERATE RISK AREA. A STATIONARY FRONT IS CURRENTLY POSITIONED FROM SWRN OK EXTENDING NEWD ACROSS SRN MO AND THIS BOUNDARY WILL BE THE FOCUS FOR CONVECTIVE DEVELOPMENT THIS AFTERNOON. THE ETA/ETAKF AND GFS ARE ALL CONSISTENT DEVELOPING A STRONG VORTICITY MAX AND MOVING IT EWD ACROSS THE TX PANHANDLE INTO OK THIS AFTERNOON.. THIS WILL SPREAD STRONG LARGE-SCALE ASCENT ACROSS REGION WHICH SHOULD COINCIDE WELL WITH PEAK HEATING AND THE STRONGEST INSTABILITY. IN ADDITION...THE EXIT REGION OF A MID TO UPPER-LEVEL JET WILL BE IN PLACE ACROSS OK AND THIS WILL PROVIDE STRONG DIVERGENCE ALOFT. AS A RESULT...EXPECT CONVECTIVE INITIATION DURING THE AFTERNOON TO BEGIN ACROSS CNTRL OK AND SPREAD EWD ACROSS THE MODERATE RISK AREA DURING THE LATE AFTERNOON AND EVENING HOURS. THE MID-LEVEL FLOW WILL INCREASE DURING THE DAY AND THIS WILL PROVIDE STRONG DEEP LAYER SHEAR OF 50 TO 60 KT FAVORABLE FOR SUPERCELL CLUSTERS. A PLUME OF STEEP LAPSE RATES ASSOCIATED WITH THE EXIT REGION OF THE MID-LEVEL JET WILL MAKE LARGE HAIL A THREAT WITH THE STORMS. FORECAST SOUNDINGS FOR ERN OK SHOW STRONG LOW-LEVEL VEERING WITH 0-3 STORM RELATIVE HELICITY ABOVE 400 M2/S2 THIS AFTERNOON. AS THE LOW-LEVEL JET INCREASES BETWEEN 22Z-02Z...CONDITIONS WILL BE FAVORABLE FOR TORNADOES WITH A FEW SIGNIFICANT TORNADOES POSSIBLE. THE MOST FAVORABLE AREA FOR STRONG TORNADOES SHOULD BE ACROSS THE ERN HALF OF OK AND IN WRN AR ALONG THE NW EDGE OF THE LOW-LEVEL JET AXIS. THE COMBINATIONS OF STEEP LAPSE RATES...STRONG DEEP LAYER SHEAR AND STRENGTHENING LOW-LEVEL FLOW WILL CONTINUE TO PRODUCE A LARGE HAIL AND WIND DAMAGE THREAT AS THE SUPERCELL CLUSTERS TRACK EWD ACROSS AR OVERNIGHT. ...OH AND TN VALLEYS/UPPER OH VALLEY... A COLD FRONT WILL MOVE SEWD ACROSS IL/IND AND OH TODAY. CONVECTION WILL LIKELY BE ONGOING ALONG THE FRONT THIS MORNING AND WILL GRADUALLY MOVE INTO THE WARM SECTOR DURING THE DAY. AS THE LINE INTERACTS WITH THE LOW-LEVEL JET ACROSS OH...KY AND TN DURING THE AFTERNOON...ISOLATED WIND DAMAGE WILL BE POSSIBLE ESPECIALLY NEAR PEAK HEATING WITH BOWING SEGMENTS. PARTIAL CLEARING SHOULD OCCUR BEHIND THE LINE NEAR THE FRONTAL BOUNDARY AND THIS WILL FOCUS AN AXIS OF INSTABILITY FROM IND SWD ALONG THE MID MS RIVER VALLEY. AS SFC HEATING OCCURS...STRONG INSTABILITY SHOULD DEVELOP ALONG THE WRN EDGE OF THE SLIGHT RISK AREA. IN ADDITION...MID-LEVEL LAPSE RATES WILL BE BETTER IN THIS CORRIDOR AND A THREAT FOR LARGE HAIL SHOULD EXIST WITH THE STRONGER UPDRAFTS. ...MID-ATLANTIC STATES... SFC ANALYSIS CURRENTLY SHOWS A MOIST AXIS IN PLACE ACROSS ERN VA AND MD WITH SFC DEWPOINTS IN THE UPPER 50S AND LOWER 60S F. LOW-LEVEL FLOW WILL INCREASE TODAY AS AN UPPER-TROUGH APPROACHING THE GREAT LAKES...SHIFTING THE LOW-LEVEL JET NEWD ACROSS THE NEW ENGLAND STATES. THIS WILL LIKELY ADVECT THE LOW-LEVEL MOISTURE INTO ACROSS MD AND SRN PA THIS AFTERNOON. A WARM FRONTAL BOUNDARY EXISTS EAST OF THE MOIST AXIS AND THIS WILL BE A FOCUS FOR STORM INITIATION. STORMS SHOULD DEVELOP ALONG THE BOUNDARY AND SPREAD NEWD INTO THE NEW ENGLAND STATES. FORECAST SOUNDINGS SHOW 30 TO 35 KT OF DEEP LAYER SHEAR AND THIS SHOULD SUPPORT MULTICELL STORMS. THIS COMBINED WITH COLD MID-LEVEL TEMPS MAY BE ENOUGH FOR MARGINAL HAIL OR STRONG WIND WITH THE CONVECTION. ..BROYLES/CROSBIE.. 04/21/2004