The SPC is forecasting ...severe thunderstorms expected over parts of the gulf coast states this afternoon and tonight.... Please read the latest public statement about this event.
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SPC AC 270055 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0755 PM CDT SAT MAR 26 2011 VALID 270100Z - 271200Z ...THERE IS A MDT RISK OF SVR TSTMS IN AN ARC FROM PORTIONS SERN GA ACROSS CENTRAL/WRN GA TO ERN/NRN AL... ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING MDT RISK FROM PORTIONS E TX TO CENTRAL/SRN GA AND SRN SC.... ...SYNOPSIS... PATTERN ALOFT WILL REMAIN CHARACTERIZED BY SPLIT FLOW OVER NRN CONUS/SRN CANADA...WITH BROAD AND NEARLY ZONAL SRN-STREAM BELT FROM GREAT BASIN ACROSS CENTRAL/SRN ROCKIES TO MIDDLE/SRN ATLANTIC COAST REGION. MID-UPPER CYCLONE NOW MOVING ASHORE PAC NW SHOULD WEAKEN INLAND...HOWEVER NEGATIVELY-TILTED SRN PORTION OF ACCOMPANYING SHORTWAVE TROUGH WILL MOVE EWD TO ID/UT OVERNIGHT. ASSOCIATED CONVECTION MAY YIELD VERY BRIEF/ISOLATED THUNDER...BUT TOO THINLY DISTRIBUTED TO WARRANT GEN TSTM AREA. FARTHER DOWNSTREAM...SHORTWAVE TROUGH THAT WAS OVER CENTRAL ROCKIES LAST NIGHT IS ACCELERATING EWD ACROSS OH VALLEY...KY AND NRN TN..AND LOSING AMPLITUDE AS IT MOVES INTO REGIME OF CONFLUENT MID-UPPER FLOW. THIS PERTURBATION WILL CONTINUE WEAKENING AS IT MOVES OFFSHORE TIDEWATER/DELMARVA REGION OVERNIGHT. ASSOCIATED SFC LOW -- ANALYZED AT 23Z OVER N-CENTRAL AL -- SHOULD MOVE SLOWLY EWD ALONG FOREGOING WARM FRONT THAT NOW EXTENDS SEWD ACROSS CENTRAL GA NEAR MCN. AFTER 06Z...EXPECT WEAK LOW TO DEVELOP OFFSHORE NC ALONG ERN SEGMENT OF SAME FRONT. INVERTED TROUGH WILL CONTINUE TO EXTEND FROM LOW NEWD OVER SRN/CENTRAL APPALACHIANS. SECONDARY SFC LOW OVER SERN AR/NWRN LA AREA OS EXPECTED TOP WEAKEN THROUGH REMAINDER EVENING AS MID-UPPER WAVE MOVES FARTHER AWAY FROM THIS AREA. COLD FRONT -- DRAWN AT 23Z FROM AL LOW SWWD ACROSS NERN/W-CENTRAL MS...EXTREME SRN AR...THROUGH SECONDARY LOW TO NE AND CENTRAL TX -- WILL OVERTAKE DRYLINE NOW ANALYZED OVER SRN HILL COUNTRY REGION OF TX. COLD FRONT SHOULD REACH WRN AL...SRN MS...SERN LA...AND MIDDLE TX COAST BY END OF PERIOD. NRN/ERN GA PORTION OF FRONTAL ZONE -- REINFORCED BY COLD DAMMING REGIME AND PRECIP TO ITS N...MAY NOT RETREAT NWD MUCH...IF AT ALL. ...LOWER MS VALLEY TO SC... ADDITIONAL MESOANALYSIS REVEALS BAROCLINIC BOUNDARY SW OF AND PARALLEL TO GA/AL WARM FRONTAL SEGMENT...EXTENDING AT 00Z FROM NEAR ABY...25 E MGM...20 S BHM...THEN CURVING NWD INTO SFC LOW ABOUT HALFWAY BETWEEN TCL-HSV. BOUNDARY IS RELATED TO COMBINATION OF TSTM OUTFLOW TO ITS NE...AND DIFFERENTIAL HEATING/MIXING ZONE DEMARCATING WELL-MIXED/DRIER BOUNDARY LAYER TO ITS SW FROM MORE MOIST AIR NEARER TO WARM FRONT. 00Z BMX RAOB APPEARED TO SAMPLE PROXIMITY OF THIS BOUNDARY FAIRLY WELL. TRANSITION ZONE FROM DRIER/MIXED AIR FROM THIS BOUNDARY THROUGH WARM FRONTAL ZONE REPRESENTS RELATIVELY MAXIMIZED POTENTIAL FOR SUSTAINED SUPERCELLS AND ACCOMPANYING TORNADOES AND LARGE HAIL. OTHERWISE...ADDITIONAL DEVELOPMENT IS POSSIBLE ALONG SFC COLD FRONT ACROSS MS/AL THAT MAY MOVE SEWD EITHER INTO THAT TRANSITION ZONE...OR INTO DRIER AIR WITH SOMEWHAT MORE VEERED FLOW OVER MS AND WRN AL...BUT STILL FAVORABLE DEEP-LAYER SHEAR. ERN LOBE OF TRANSITIONAL AIR MASS MAY EXTEND EWD ACROSS SRN GA. BUOYANCY SHOULD CONTINUE TO DIMINISHING CONSIDERABLY NEWD INTO SC WHERE PERSISTENT PRECIP WILL REINFORCE BOUNDARY-LAYER STATIC STABILITY. WELL N OF WARM FRONT...OVER MOUNTAINS...MAIN THREAT WILL BE HAIL ATOP RELATIVELY STABLE BOUNDARY LAYER...BUT WITH FAVORABLE ELEVATED BUOYANCY AND EFFECTIVE SHEAR ALOFT. REF SPC WWS 63-65...AND RELATED MESOSCALE DISCUSSIONS...FOR MORE COVERAGE OF NEAR-TERM SVR THREAT ACROSS THIS REGION. ...ARKLATEX REGION TO E TX/WRN LA... 2-3 HOUR WINDOW REMAINS FOR RELATIVELY MAXIMIZED SVR PROBABILITIES ALONG COLD FRONT...WITH ADDITIONAL DEVELOPMENT NOTED IN LAST VIS IMAGERY AND IN RADAR REFLECTIVITY LOOPS OVER PORTIONS E TX. LARGE HAIL AND DAMAGING GUSTS ARE PRIMARY CONCERNS. SVR POTENTIAL WILL DIMINISH ACROSS THIS REGION ALONG/AHEAD OF COLD FRONT AFTER ABOUT 04Z DUE TO COMBINATION OF 1. GREATER SFC DIABATIC COOLING IN WARM SECTOR... 2. PRESENCE OF VEERED FLOW DUE TO ISALLOBARIC FORCING AHEAD OF DEPARTING SFC LOW...LEADING TO REDUCTION IN BOTH SHEAR AND LOW-LEVEL CONVERGENCE...AND 3. LACK OF ANY SIGNIFICANT MID-UPPER LEVEL SUPPORT OTHER THAN STRONG ZONAL FLOW IN 250-500 MB LAYER. ..EDWARDS.. 03/27/2011 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0600Z