MESOSCALE DISCUSSION 0487
   NWS STORM PREDICTION CENTER NORMAN OK
   0319 AM CDT WED APR 20 2011
   
   AREAS AFFECTED...NRN AL
   
   CONCERNING...TORNADO WATCH 160...165...
   
   VALID 200819Z - 200945Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 160...165...CONTINUES.
   
   AN ADDITIONAL WATCH MAY BE NEEDED ACROSS PARTS OF NORTHERN
   ALABAMA...LIKELY REPLACING WW 160...WITHIN THE NEXT HOUR OR SO.
   
   BROAD UPPER TROUGHING IS BEGINNING TO LIFT NORTHEAST OF THE MIDDLE
   MISSISSIPPI VALLEY REGION...BUT FORCING FOR UPWARD VERTICAL MOTION
   REMAINS STRONG ENOUGH TO SUPPORT CONTINUING CONVECTIVE DEVELOPMENT
   AHEAD OF AN ASSOCIATED SURFACE COLD FRONT AS FAR SOUTH AS THE NORTH
   CENTRAL GULF STATES.  THIS FORCING APPEARS LIKELY TO SPREAD ACROSS
   NORTHERN ALABAMA AND MIDDLE/EASTERN TENNESSEE...INTO THE SOUTHERN
   APPALACHIANS...BETWEEN NOW AND 11-13Z...ACCOMPANIED BY STRONG/SEVERE
   STORMS.  MOIST LOW-LEVELS AND STEEP MID-LEVEL LAPSE RATES ARE
   CONTRIBUTING TO MODERATELY LARGE CAPE UP TO AROUND 2000 J/KG ACROSS
   THE REGION...IN THE PRESENCE OF STRONG SHEAR BENEATH 50 KT WESTERLY
   500 MB FLOW.  LARGE HAIL MAY BE THE PRIMARY THREAT ACROSS NORTHERN
   ALABAMA...BUT CONDITIONS COULD STILL REMAIN SUFFICIENT FOR THE
   DEVELOPMENT OF ANOTHER VIGOROUS COLD POOL CAPABLE OF SUPPORTING
   POTENTIALLY DAMAGING WIND GUSTS.
   
   ..KERR.. 04/20/2011
   
   
   ATTN...WFO...FFC...BMX...HUN...MEG...JAN...
   
   LAT...LON   33668832 34858756 34858549 33938548 33358610 33088738
               33668832