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Feb 20, 2014 1630 UTC Day 1 Convective Outlook

February 20, 2014

Feb 20, 2014 1630 UTC Day 1 Convective Outlook

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DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1030 AM CST THU FEB 20 2014

VALID 201630Z – 211200Z

…THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON/EVENING FROM NRN MS ACROSS NW AL…WRN/MIDDLE TN…AND WRN/CENTRAL KY…

…THERE IS A SLGT RISK OF SVR TSTMS FROM THE NRN GULF COAST TO THE OH VALLEY…

…WIDESPREAD DAMAGING WINDS AND A FEW TORNADOES POSSIBLE LATER THIS AFTERNOON THROUGH EARLY TONIGHT FOR PARTS OF THE MID SOUTH AND TN/OH VALLEYS…

…MS/OH/TN VALLEY REGION THROUGH TONIGHT…
A STRONG MIDLEVEL SHORTWAVE TROUGH WILL PROGRESS EWD/NEWD FROM THE CENTRAL PLAINS TO THE MID MS VALLEY AND GREAT LAKES BY LATER TONIGHT. AT THE SURFACE…A RAPIDLY DEEPENING CYCLONE WILL TRANSLATE FROM THE KANSAS CITY AREA THIS MORNING TO WI/UPPER MI OVERNIGHT. S OF THE LOW…A COLD FRONT WILL SWEEP QUICKLY EWD TO THE MS RIVER BY THIS EVENING…AND THE TN/OH VALLEYS OVERNIGHT. SEASONABLY RICH MOISTURE IS SPREADING NWD/NEWD IN THE WARM SECTOR OF THE CYCLONE…BENEATH A STEEP LAPSE RATE PLUME PER REGIONAL 12Z SOUNDINGS. THE RELATIVELY WARM ELEVATED MIXED LAYER WILL ACT TO CAP THE BOUNDARY LAYER UNTIL EARLY-MID AFTERNOON…AND RELATIVELY WIDESPREAD CLOUDS WILL SLOW SURFACE HEATING SOMEWHAT. STILL…ASCENT IN ADVANCE OF THE MIDLEVEL WAVE AND ALONG THE FRONT WILL WEAKEN THE CAP FROM BELOW AND LIKELY SUPPORT THUNDERSTORM DEVELOPMENT BY 19-21Z.

THERE APPEAR TO BE TWO POTENTIAL CORRIDORS FOR CONVECTIVE INITIATION…THE IMMEDIATE COLD FRONT FROM THE SAINT LOUIS VICINITY SWD INTO NE AR BY MID AFTERNOON…AND A SLIGHTLY PRE-FRONTAL CONFLUENCE BAND ALONG THE AXIS OF RICHEST LOW-LEVEL MOISTURE FROM E CENTRAL TX ACROSS NW LA TO THE MEMPHIS AREA BY 21Z. STRONG CROSS-FRONTAL FLOW/SHEAR VECTORS AND A CORRIDOR OF STRONGER SURFACE HEATING WILL SUPPORT A RISK FOR SUPERCELL DEVELOPMENT INITIALLY ALONG THE COLD FRONT FROM SAINT LOUIS INTO NE AR THIS AFTERNOON IN A ZONE OF MLCAPE OF 500-1000 J/KG AND VERY STRONG DEEP-LAYER VERTICAL SHEAR. DAMAGING WINDS AND A COUPLE OF TORNADOES WILL BE POSSIBLE S OF THE MORE STABLE BOUNDARY LAYER AND EXISTING SNOW PACK. THE SRN PRE-FRONTAL CONVECTION WILL POTENTIALLY INCLUDE EMBEDDED SUPERCELLS THIS AFTERNOON/EVENING…THOUGH CONVECTIVE MODE IS A BIT IN QUESTION GIVEN THE OBSERVED AND FORECAST VEER-BACK PROFILE AROUND 700 MB ACROSS THE ARKLAMISS/MID SOUTH.

EVEN WITH POTENTIALLY TWO MODES/ZONES OF INITIAL CONVECTION…
CONSOLIDATION INTO A SQUALL LINE IS EXPECTED BY THIS EVENING/EARLY TONIGHT…WITH A MORE WIDESPREAD DAMAGING WIND RISK IN THE MDT RISK AREA. THE NRN PORTIONS OF THE SQUALL LINE WILL LIKELY WEAKEN LATE TONIGHT TOWARD THE UPPER OH VALLEY AND JUST W OF THE APPALACHIANS…WHILE THE DAMAGING WIND/ISOLATED TORNADO RISK WILL PERSIST THROUGH THE NIGHT FROM SE LA ACROSS MS/AL TO NW GA IN THE CORRIDOR OF RICHEST LOW-LEVEL MOISTURE AND CONTINUING STRONG VERTICAL SHEAR.

…NRN MO TO SRN WI THROUGH THIS AFTERNOON…
CLUSTERS OF ELEVATED THUNDERSTORMS WILL LIKELY PERSIST IN THE ZONE OF ASCENT/ELEVATED BUOYANCY PRECEDING THE DEEPENING SURFACE LOW THROUGH THE AFTERNOON. MARGINALLY SEVERE HAIL WILL BE POSSIBLE…REFERENCE MD 119 FOR ADDITIONAL DETAILS.

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