MESOSCALE DISCUSSION 0449
   NWS STORM PREDICTION CENTER NORMAN OK
   0506 PM CDT THU APR 11 2013
   
   AREAS AFFECTED...EASTERN TN AND IMMEDIATELY ADJACENT PORTIONS OF
   NC/KY/VA
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 112206Z - 112330Z
   
   PROBABILITY OF WATCH ISSUANCE...60 PERCENT
   
   SUMMARY...A WATCH MAY BE NEEDED FOR EASTERN TN AND PERHAPS
   IMMEDIATELY ADJACENT PARTS OF NC/KY/VA FOR AN INCREASING SEVERE
   THREAT THIS EVENING...WITH DAMAGING WINDS AND SOME TORNADO THREAT.
   
   DISCUSSION...A RELATIVELY WELL-ORGANIZED QUASI-LINEAR CONVECTIVE
   SYSTEM CONTINUES TO STEADILY PROGRESS EAST-NORTHEASTWARD /GENERALLY
   35-40 KT/ ACROSS NORTH-CENTRAL/NORTHEAST AL...NOW EAST OF I-65 AND
   NEAR THE HUNTSVILLE AREA AS OF 2145Z...AND EAST-CENTRAL TN. THIS
   INCLUDES SOME SEMI-DISCRETE STORMS/POSSIBLE SUPERCELLS IMMEDIATELY
   AHEAD OF THE QLCS. THIS ACTIVITY...THE QLCS AND POSSIBLE
   LINE-LEADING SUPERCELLS...IS EXPECTED TO CONTINUE TO PROGRESS INTO
   EASTERN TN/FAR WESTERN NC AND SURROUNDING AREAS THROUGH EARLY
   EVENING. SCENARIO MAY BE INFLUENCED ON THE LARGE SCALE BY A
   NORTHEAST-ADVANCING SHORTWAVE TROUGH/JET STREAK APPROACHING THE TN
   VALLEY TONIGHT AND CORRESPONDING OHIO VALLEY SURFACE
   CYCLOGENESIS...ALONG WITH SOME EASTWARD ACCELERATION OF THE UPSTREAM
   COLD FRONT.
   
   THE BOUNDARY LAYER IMMEDIATELY AHEAD OF THE QLCS IS CHARACTERIZED BY
   MODESTLY HIGH TEMP-DEWPOINT SPREADS AS MUCH AS 15-20 F AS OF
   22Z...WITH RELATIVELY WEAK LOW-LEVEL SHEAR CURRENTLY NOTED PER THE
   MORRISTOWN WSR-88D VWP. HOWEVER...SURFACE T-TD SPREADS SHOULD
   CONTINUE TO LOWER TOWARD/AFTER SUNSET...AND LOW-LEVEL SHEAR IS
   LIKELY TO MARKEDLY INCREASE OVER THE NEXT FEW HOURS VIA A
   STRENGTHENING SOUTHERLY LOW LEVEL JET...A TREND WELL NOTED IN
   UPSTREAM OBSERVATIONS SUCH AS THE HUNTSVILLE WSR-88D VWP /AROUND 350
   M2 PER S2 0-1 KM SRH/. IN ALL...BOUTS OF DAMAGING WINDS AND PERHAPS
   A TORNADO OR TWO WILL BE A POSSIBILITY IN A SOUTHWEST-NORTHEASTWARD
   CORRIDOR ACROSS EASTERN TN AND PERHAPS IMMEDIATELY SURROUNDING AREAS
   INTO THIS EVENING.
   
   ..GUYER/CORFIDI.. 04/11/2013
   
   
   ATTN...WFO...GSP...MRX...JKL...OHX...HUN...
   
   LAT...LON   35068347 35028432 35098564 35188605 35948552 36458468
               36658332 35998261 35188288 35068347