DAY 1 CONVECTIVE OUTLOOKNWS STORM PREDICTION CENTER NORMAN OK0729 AM CDT SUN MAY 03 2009 VALID 031300Z - 041200Z …THERE IS A MDT RISK OF SVR TSTMS FROM PARTS OF CENTRAL/NRN LAACROSS CENTRAL MS INTO CENTRAL AL… …THERE IS A SLGT RISK OF SVR TSTMS FROM ERN TX INTO THE SOUTHERNAPPALACHIANS… …THERE IS A SLGT RISK OF SVR TSTMS ACROSS SERN VA/NRN NC… …ERN TX/LOWER MS RIVER VALLEY INTO THE SRN APPALACHIANS…WELL DEFINED SHORTWAVE TROUGH NOW OVER TX WILL CONTINUE EJECTINGENEWD ACROSS THE LOWER MS RIVER VALLEY/MID SOUTH TODAY. AT THESURFACE…COMPOSITE OUTFLOW BOUNDARY/FRONT FROM THE LOWER TN RIVERVALLEY INTO CENTRAL LA AT 12Z WILL LIKELY REMAIN STALLED OR SAGSLOWLY SSEWD THROUGH THE AFTERNOON. SURFACE DEW POINTS IN THE UPPER60S/LOWER 70S F WILL PERSIST AHEAD OF THE FRONT AND SUPPORT MODERATETO STRONG INSTABILITY ACROSS THE WARM SECTOR WITH AFTERNOON HEATING.THIS WILL ALSO ALL BUT ELIMINATE CAPPING BY THE EARLY TO MIDAFTERNOON NEAR THE FRONT. ONGOING CLUSTERS OF ELEVATED STORMS MAY CONTINUE THROUGH THE MORNINGFROM NRN LA INTO NRN/CENTRAL MS. SMALL LEADING LINE OF STORMS OVERCENTRAL MS THIS MORNING MAY CONTINUE TO BE FED BY RESERVOIR OFMODERATE INSTABILITY IN PLACE ACROSS WARM SECTOR. ISOLATED SEVEREMAY ACCOMPANY THIS CLUSTER OF STORMS INTO WRN AL THIS MORNING.HOWEVER…PRIMARY SEVERE THREAT IS EXPECTED TO EVOLVE AS A POSSIBLEDERECHO MCS FROM ACTIVITY MOVING OUT OF ERN TX AT 12Z. PRIMARY AXISOF WIND DAMAGE THREAT SHOULD EXTEND ENEWD ACROSS THE LOWER MS RIVERVALLEY AND INTO PORTIONS OF AL THROUGH THE AFTERNOON INVOF EFFECTIVESURFACE FRONT. AT SOME POINT THIS MCS MAY RACE ENEWD ACROSS LAFASTER THAN PRECEEDING AIR MASS CAN DESTABILIZE. HOWEVER…WITHSTRONG/DEEP ASCENT AND CONTINUED DESTABILIZATION THIS AFTERNOONACTIVITY SHOULD CYCLE UPWARDS OR REGENERATE NEARER THE UPPER SYSTEMBY THE EARLY AFTERNOON. IN ADDITION TO POSSIBLE WIDESPREAD WINDDAMAGE…LOW LEVEL SHEAR WILL REMAIN QUITE STRONG UNDER 40-50 KTWSWLY H85 FLOW SUPPORTING A THREAT OF TORNADOES BOTH FROM LEADINGSUPERCELLS AND FROM EMBEDDED SUPERCELLS WITHIN THE DERECHO MCS.SECONDARY BOWING MCS/CLUSTER OF SUPERCELLS MAY EVOLVE SW OF THELEADING SYSTEM DURING THE AFTERNOON AS CAP WEAKENS/BREAKS ALONGSURFACE COLD FRONT ADVANCING SEWD ACROSS THE LOWER MS RIVER VALLEY.THIS ACTIVITY WOULD THEN TRACK QUICKLY ENEWD POSSIBLY INTO NRN GABEFORE WEAKENING THIS EVENING. MID/UPPER TROUGH AXIS IS FORECAST TOREMAIN ACROSS THE LOWER MS RIVER VALLEY/CENTRAL GULF COAST STATESOVERNIGHT…SUGGESTING SUFFICIENT LIFT/SHEAR WILL REMAIN IN PLACEACROSS THE SRN APPALACHIANS FOR CONTINUED SEVERE THREAT INTO MONDAYMORNING…DEPENDANT ON QUALITY OF INSTABILITY LATE IN THE PERIOD. …NRN NC/SRN VA…AT THE SFC…A LOW WILL MOVE QUICKLY EWD ACROSS TN VALLEY INTO THESRN APPALACHIANS AS A WARM FRONT MOVES SLOWLY NWD ACROSS NRN NC INTOSRN VA BY MID-AFTERNOON. THUNDERSTORMS SHOULD DEVELOP ALONG THEBOUNDARY IN THE HIGHER TERRAIN OF NRN NC AND INVOF THE FRONT DURINGTHE MID TO LATE AFTERNOON AS CAP WEAKENS AND AIR MASS BECOMESMODERATELY UNSTABLE. MODEST DEEP LAYER SHEAR WILL REMAIN IN PLACEACROSS THIS REGION UNDER 35-45 KT SWLY H5 FLOW. THIS SHOULD BESUFFICIENT FOR ORGANIZED CLUSTERS AND POSSIBLY ISOLATED SUPERCELLSAS INSTABILITY IS MAXIMIZED THIS AFTERNOON. THE MOST FAVORABLESEVERE THREAT MAY BE DAMAGING WIND GUSTS DUE TO UNIDIRECTIONAL WINDPROFILES AND STRONG LOW-LEVEL FLOW. IF ENOUGH INSTABILITY CANMATERIALIZE…THEN A CLUSTER OF STORMS WITH HAIL POTENTIAL WOULDALSO BE POSSIBLE. …SRN ID/NRN UT/SW WY…ZONAL FLOW WILL BE IN PLACE TODAY ACROSS THE INTERMOUNTAIN WEST AS AMID-LEVEL JET MOVES INLAND ACROSS THE NRN COAST OF CA. AS SFC TEMPSWARM…THUNDERSTORMS SHOULD INITIATE THIS AFTERNOON ACROSS PARTS OFTHE INTERMOUNTAIN WEST. THE EXIT REGION OF THE MID-LEVEL JET ISFORECAST TO SPREAD EWD ACROSS SRN ID AND NRN UT LATE THIS AFTERNOONRESULTING IN STRONG VERTICAL SHEAR PROFILES. THIS COMBINED WITHSTEEP MID-LEVEL LAPSE RATES SHOULD BE ENOUGH FOR A MARGINAL SEVERETHREAT WITH THE STRONGER CELLS. ..EVANS/GARNER.. 05/03/2009
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