The SPC is forecasting ...a significant severe weather episode is expected over parts of the lower ohio valley...tennessee valley into lower mississippi valley this afternoon and tonight....   Please read the latest public statement about this event.  View What is a Watch? clip.

   SPC AC 201630

   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.

   ..THOMPSON/LEITMAN.. 02/20/2014

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z