The SPC is forecasting ...widespread severe thunderstorms expected over the western half of the southern and central plains this afternoon and tonight.... Please read the latest public statement about this event.
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SPC AC 280544 DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1244 AM CDT WED MAR 28 2007 VALID 281200Z - 291200Z ...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF THE GREAT PLAINS FROM NWRN TEXAS AND THE EASTERN TEXAS PANHANDLE...WESTERN OKLAHOMA...KANSAS AND SOUTH-CENTRAL NEBRASKA... ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK AREA FROM THE RIO GRANDE VALLEY OF TX NWD TO EXTREME ERN WY AND MUCH OF SD... ...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE CNTRL APPALACHIANS...PARTS OF SRN VA...AND MUCH OF NC...NWRN SC... ...LATEST INDICATIONS SHOW INCREASING CHANCES FOR AN EXTENSIVE SWATH OF SEVERE STORMS ACROSS THE GREAT PLAINS LATER TODAY AND TONIGHT... ...SYNOPSIS... LARGE DEEP-LAYER CYCLONE CONTINUES TO EVOLVE ACROSS THE INTERMOUNTAIN WEST LATE TONIGHT WITH 110KT MID LEVEL JET MAX TRANSLATING THROUGH THE BASE OF THE TROUGH OVER THE LOWER CO RIVER VALLEY. EXTENSIVE AREA OF PRONOUNCED MID AND UPPER LEVEL DIFFLUENCE AHEAD OF STRONG DPVA WILL OVERSPREAD THE HIGH PLAINS THROUGH LATE TODAY COINCIDENT WITH PACIFIC COLD FRONT DEVELOPING EAST OF THE ROCKIES. ASSOCIATED LEE-SIDE SURFACE LOW WILL BEGIN THE DAY OVER ERN CO/WY AND THEN TRACK ENEWD ACROSS THE NEB PNHDL AND WRN SD AS MID/UPPER LEVEL CIRCULATION CLOSES OFF ACROSS WY/CO THROUGH EARLY THURSDAY. IN THE EAST...A LOW AMPLITUDE SHORT WAVE TROUGH WILL CREST RAPIDLY AMPLIFYING LARGE SCALE UPPER RIDGE AND SPREAD SEWD ACROSS THE CNTRL APPALACHIANS THROUGH TONIGHT. ALTHOUGH HEIGHT FALLS WITH THIS IMPULSE ARE MEAGER...A BACK-DOOR FRONT SPREADING SWWD ACROSS VA/NC WILL ACT AS A FOCUS FOR STRONGER ASCENT AND SHEAR COINCIDENT WITH PEAK IN DIURNAL DESTABILIZATION ACROSS THESE AREAS. ...CNTRL/NRN GREAT PLAINS... AS THE STRONG PACIFIC FRONT SURGES EAST ACROSS THE HIGH PLAINS LATER TODAY IT APPEARS THAT IT WILL PROBABLY OVERTAKE DRYLINE FORMATION ACROSS PARTS OF NRN KS/SRN NEB. A WEAK QUASI-STATIONARY BOUNDARY ALONG THE KS/NEB BORDER MAY ACT AS A WARM FRONT WHERE STRONGER FORCING AND SHEAR CAN DEVELOP NEAR THE INTERSECTION WITH THE COLD FRONT. TRUE WARM FRONT WITH LARGER SCALE SYSTEM IS HARDER TO DEFINE BASED ON RAPID INTENSIFICATION AND EXTENSIVE NATURE OF THE LOW LEVEL SLY FLOW DEVELOPING ACROSS THE PLAINS...AND LIMITED N-S AIR MASS DISCONTINUITY. HOWEVER...A SECONDARY AREA OF ENHANCED FORCING WILL LIKELY OCCUR NEAR AND SE OF THE CENTER OF THE OCCLUDING SURFACE LOW...FROM EXTREME ERN WY/MT ACROSS WRN PARTS OF SD/NEB LATER THIS AFTERNOON THROUGH THIS EVENING. SURFACE DEWPOINTS ARE FORECAST TO RANGE FROM THE 50S NORTH TO LOWER 60S ACROSS NCNTRL KS. SLIGHTLY COOLER TEMPERATURES ALOFT ACROSS NRN PARTS OF THE PLAINS WILL OFFSET MORE LIMITED MOISTURE. A FAIRLY UNIFORM PLUME OF SURFACE-BASED DESTABILIZATION /MLCAPE 1000-1500 J PER KG/ IS EXPECTED TO DEVELOP IN ADVANCE OF THE COLD FRONT FROM SWRN SD TO NRN KS BY LATE AFTERNOON. GIVEN MAGNITUDE OF LARGE SCALE FORCING FOCUSED ALONG THE FRONT...AND ENHANCED MESOSCALE FORCING NEAR AFOREMENTIONED FEATURES...RAPID TSTM DEVELOPMENT IS INDICATED IN ALL AVAILABLE GUIDANCE BY ABOUT 21Z. AMBIENT DEEP-LAYER SHEAR WILL SUPPORT RAPIDLY MOVING STORMS WITH PERSISTENT/ORGANIZED UPDRAFTS CAPABLE OF PRODUCING VERY LARGE HAIL...DAMAGING WINDS...AND POSSIBLY A COUPLE OF STRONG TORNADOES. INCREASING MERIDIONAL COMPONENT OF MEAN WIND AND DEEP-LAYER SHEAR VECTORS ORIENTED ALONG THE LINE OF FRONTAL FORCING SUGGEST THAT CONVECTION MAY EVOLVE RATHER RAPIDLY INTO QLCS WITH BOWING LINE SEGMENTS MOVING AT AROUND 50KT SPREADING DAMAGING WINDS EWD/NEWD ACROSS CNTRL NEB AND NCNTRL KS THROUGH THE NIGHT. CONVECTION WILL ALSO DEVELOP EWD INTO STRONGLY BACKED SURFACE FLOW WHERE EFFECTIVE SRH AROUND 300 M2/S2 WILL PROVIDE MORE THAN AN ADEQUATE ENVIRONMENT FOR A COUPLE OF POTENTIALLY STRONG TORNADOES. GREATER TORNADIC POTENTIAL WILL OCCUR WITH ANY DISCRETE CELLS...OR LINE BREAKS...IN PROXIMITY TO BOUNDARY INTERSECTIONS AND OTHER MESOSCALE FEATURES WHERE STORM SCALE INFLOW/DYNAMICS WILL BE LOCALLY ENHANCED. ...SRN GREAT PLAINS... FARTHER SOUTH...SEPARATION BETWEEN DRYLINE AND COLD FRONT MAY BE GREATER FROM SWRN KS ACROSS OK/TX. SITUATION APPEARS FAVORABLE FOR DRYLINE SUPERCELL INITIATION ACROSS THESE AREAS PRIOR TO COLD FRONT ADVANCING EAST AND MERGING WITH THE DRYLINE...MOST LIKELY AFTER DARK. HERE TOO...ENVIRONMENT APPEARS VERY SUPPORTIVE OF MYRIAD OF SEVERE WEATHER THREATS AS EFFECTIVE BULK SHEAR INCREASES TO OVER 40KT ACROSS STRONGLY UNSTABLE AIR MASS CHARACTERIZED BY MLCAPE OF AT LEAST 2000 J/KG. OTHER THAN CONFLUENCE ZONE NEAR THE DRYLINE...LACK OF STRONGLY DEFINED MESOSCALE BOUNDARIES IN THE WARM SECTOR SUGGEST CELLS MAY REMAIN DISCRETE IN NATURE AS EFFECTIVE SRH LOCALLY INCREASES TO OVER 300 M2/S2 THROUGH 00Z. SPC ANALOG SOUNDING SYSTEM REVEALS A FEW SIGNIFICANT TORNADO MATCHES BASED ON NAM-WRF FORECAST SOUNDINGS FROM NWRN TX/WRN OK VALID AROUND 00Z. PRESENT INDICATIONS BASED ON A VARIETY OF MODEL GUIDANCE SUGGEST MOST SUPPORTIVE ENVIRONMENT FOR A STRONG TORNADO OR TWO MAY EVOLVE IN A RELATIVELY NARROW CORRIDOR FROM NWRN TX TO SWRN KS THROUGH EARLY EVENING. PROXIMITY TO GREATER LOW LEVEL MOISTURE ACROSS SRN PARTS OF THIS AREA COULD SUPPORT A COUPLE OF LONGER-TRACK DANGEROUS STORMS. ADDITIONALLY...SPC HAIL MODEL BASED ON NAM-WRF INPUT SOUNDINGS GENERATES HAILSTONE DIAMETERS OF 1-3 INCHES ACROSS MUCH OF THE SRN PLAINS AREA WHERE STORM INITIATION IS ANTICIPATED LATER THIS AFTERNOON. TENDENCY FOR STORM MERGERS AND INCREASING FORCING ALONG THE ADVANCING COLD FRONT WILL LEAD TO QLCS DEVELOPMENT AFTER DARK. SLOW EWD TRANSITION OF THE LARGE SCALE TROUGH BY THIS TIME SUGGESTS THAT CONVECTIVE SYSTEM WILL ALSO BE SLOW TO DEVELOP EWD. THIS MAY RESULT IN A CONTINUING THREAT FOR DAMAGING WINDS.... HAIL...AND HEAVY RAIN OVER THE SAME AREAS THROUGH LATE TONIGHT. ...SW TX... STORM COVERAGE MAY BE LESS ACROSS PARTS OF SWRN TX DUE TO THIS AREA BEING FARTHER REMOVED FROM STRONGER LARGE SCALE FORCING. HOWEVER...MIXING ALONG THE DRYLINE COUPLED WITH WEAK HEIGHT FALLS AND VERY STRONG INSTABILITY COULD LEAD TO EXPLOSIVE TSTM DEVELOPMENT BY EVENING. MODELS INDICATE SOME POTENTIAL FOR SUPERCELL TORNADOES AND VERY LARGE HAIL AS FAR SOUTH AS THE RIO GRANDE. HOWEVER...POTENTIALLY FEWER STORMS DICTATE LOWER PROBABILITIES ALONG THE TRAILING PORTION OF THE DRYLINE/FRONT. ...CNTRL APPALACHIANS ACROSS PARTS OF THE CAROLINAS... STRONG HEATING AND MOISTURE FOCUS IN ADVANCE OF BACK-DOOR FRONT WILL RESULT IN THE DEVELOPMENT OF MODEST INSTABILITY FROM SWRN VA ACROSS WRN/NRN NC THROUGH THE AFTERNOON. LIFT AND SHEAR ALONG THIS BOUNDARY WILL BE REINFORCED FURTHER AS MID LEVEL IMPULSE AND ASSOCIATED 40-50KT SPEED MAX SPREAD SEWD ACROSS THE REGION. THERE IS GOOD AGREEMENT IN LATEST GUIDANCE THAT STORMS WILL INCREASE IN COVERAGE ACROSS THE APPALACHIANS...AND TRACK ESEWD ALONG THE FRONT THROUGH THE AFTERNOON. CELLS CROSSING THE FRONT FROM N TO S COULD ACQUIRE LOW LEVEL ROTATION BEFORE BECOMING ELEVATED IN STABLE POST-FRONTAL REGIME. PRIMARY THREAT APPEARS TO BE THE POTENTIAL FOR NUMEROUS HAIL EVENTS. CONVECTIVE VIGOR SHOULD DIMINISH WITHIN A COUPLE HOURS AFTER SUNSET. ..CARBIN/BOTHWELL.. 03/28/2007 CLICK TO GET WUUS01 PTSDY1 PRODUCT NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z