DAY 1 CONVECTIVE OUTLOOK CORR 1 NWS STORM PREDICTION CENTER NORMAN OK 0110 AM CDT WED APR 27 2011 VALID 271200Z - 281200Z ...THERE IS A HIGH RISK OF SVR TSTMS OVER PORTIONS OF NRN MS...AL...FAR NWRN GA AND SRN MIDDLE TN... ...THERE IS A MDT RISK OF SVR TSTMS OVER MUCH OF CNTRL AND NRN MS AND AL...NWRN GA...MUCH OF TN AND KY...WRN CAROLINAS... ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE LOWER MS VALLEY/GULF COAST STATES NWD TO THE CANADIAN BORDER... CORRECTED FOR SPELLING ERROR ...SYNOPSIS... AN UPPER TROUGH AXIS WILL BE CENTERED ACROSS THE SRN PLAINS AT 12Z WED...WITH A 100 KT MID LEVEL JET ACROSS N TX. THIS FEATURE WILL STRENGTHEN THROUGH 00Z AS IT EJECTS NEWD ACROSS THE LOWER MS AND INTO THE TN/OH VALLEYS DURING THE DAY. AT THE SURFACE...LOW PRESSURE IS FORECAST TO BE OVER W CNTRL AR AT 12Z...WITH A DEVELOPING COLD FRONT TRAILING SWWD INTO ERN TX. THESE FEATURES WILL MOVE RAPIDLY ENEWD...WITH THE SURFACE LOW NEARING SRN INDIANA BY 00Z AND A SHARP LOW PRESSURE TROUGH EXTENDING SWD INTO CNTRL KY...MIDDLE TN...ERN MS AND WRN AL. AHEAD OF THE FRONT...A VERY WARM AND MOIST AIR MASS WILL ALREADY BE IN PLACE BY MIDDAY WITH 68-72 BOUNDARY LAYER DEWPOINTS LIKELY FROM THE GULF COAST INTO MS/AL...AND MID TO UPPER 60S F OVER TN AND SRN KY WHERE SUBSTANTIAL MORNING CONVECTION WILL LIKELY BE ONGOING. WITH RELATIVELY COOL TEMPERATURE PROFILES ALOFT...AN EXTREMELY UNSTABLE ATMOSPHERE WILL RESULT ACROSS THE WARM SECTOR. WIND FIELDS THROUGHOUT THE TROPOSPHERE WILL STRENGTHEN WITH THE APPROACHING TROUGH/JET MAX...AND THE COMBINATION OF THE TWO IS EXPECTED TO RESULT IN A TORNADO OUTBREAK...WITH LONG-TRACKED STRONG TO VIOLENT TORNADOES POSSIBLE OVER THE HIGH RISK AREA. TO THE E...THE BROAD SLY FLOW ACROSS THE WARM SECTOR WILL EXTEND INTO THE MID ATLANTIC REGION...WITH A SECONDARY MOIST PLUME OFF THE ATLANTIC NWD INTO THE CAROLINAS AND WRN VA BY AFTERNOON. --- AN OUTBREAK OF TORNADOES AND DAMAGING WINDS IS EXPECTED TODAY THROUGH EVENING OVER PORTIONS OF NRN MS...NRN AL...TN AND KY. --- ...LOWER MS VALLEY INTO TN/OH VALLEYS... A COMPLICATED FORECAST SCENARIO WILL UNFOLD TODAY...BEGINNING RATHER EARLY IN THE PERIOD OVER SRN AND ERN AR AND NRN LA. MODELS ARE IN RELATIVELY GOOD AGREEMENT WITH THE PLACEMENT OF THE SURFACE LOW OVER AR BETWEEN 12-15Z...THEN DEVELOPING IT NEWD ACROSS TN/KY BY 00Z. NUMEROUS THUNDERSTORMS WILL BE ONGOING...AND SOME WILL BE SEVERE...FROM NRN LA/SRN AR EWD ACROSS NRN MS...WRN AND MIDDLE TN AND KY. DESPITE TIME OF DAY...PRESENCE OF RICH LOW LEVEL MOISTURE WILL RESULT IN LITTLE CAPPING AND SURFACE BASED EFFECTIVE PARCELS. THUS...A TORNADO AND DAMAGING WIND THREAT WILL BE PRESENT WITH THIS ACTIVITY. SOUTH OF THE ONGOING ACTIVITY...STRONG DAYTIME HEATING WILL OCCUR. WITH BOUNDARY LAYER DEWPOINTS IN THE LOW 70S F...THIS WILL CREATE STRONG TO EXTREME INSTABILITY OVER MS AND AL NWD TO THE ONGOING CONVECTION. A CAPPING INVERSION WILL LIKELY KEEP MUCH OF THE WARM SECTOR S OF THE EARLY STORMS CAPPED...ALLOWING A BUILD UP OF INSTABILITY TO BE RELEASED WHEN LARGE SCALE FORCING ARRIVES DURING THE AFTERNOON ALONG THE COLD FRONT AND ESPECIALLY NEAR THE FRONT/OUTFLOW BOUNDARY INTERSECTION. THE RESULT WILL BE FAST MOVING TORNADIC SUPERCELLS CAPABLE OF STRONG TO VIOLENT TORNADOES. GIVEN THE FAST STORM MOTIONS AND RELATIVELY WIDE WARM SECTOR...SOME TORNADOES COULD BE LONG LIVED. THE GREATEST THREAT FOR THESE TYPES OF STORMS WILL BE OVER THE HIGH RISK AREA...OVER NRN MS AND AL...INTO EXTREME NWRN GA AND SRN MIDDLE TN. THIS ACTIVITY WILL PERSIST TO THE E...BUT CELLS MAY EVENTUALLY MERGE INTO MORE OF A QLCS STRUCTURE CAPABLE OF PARTICULARLY DAMAGING WINDS AND A FEW TORNADOES. ...WRN NC/VA... A CONDITIONAL SEVERE THREAT WILL EXIST BY LATE AFTERNOON OVER WRN NC/VA. STRONG HEATING WILL RESULT IN STEEP LOW LEVEL LAPSE RATES...BUT FORECAST SOUNDINGS SHOW A CAPPING INVERSION AROUND 700 MB...WHICH SHOULD KEEP THE AIR MASS CAPPED. HOWEVER...MOISTURE ADVECTION...AS WELL AS SELY UPSLOPE FLOW MAY RESULT IN ISOLATED THUNDERSTORMS DURING THE AFTERNOON OVER THE HIGHER TERRAIN. WIND PROFILES WOULD FAVOR SUPERCELLS...CAPABLE OF PRODUCING TORNADOES HAIL AND WIND. WILL MAINTAIN LOW PROBABILITIES FOR THE DAYTIME CONVECTION. ..JEWELL.. 04/27/2011