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Mesoscale Discussion 820
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   MESOSCALE DISCUSSION 0820
   NWS STORM PREDICTION CENTER NORMAN OK
   1007 AM CDT THU MAY 08 2008
   
   AREAS AFFECTED...NRN MS...CNTRL/NRN AL INTO MIDDLE/ERN TN
   
   CONCERNING...TORNADO WATCH 277...
   
   VALID 081507Z - 081630Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 277 CONTINUES.
   
   AN ADDITIONAL WW MAY BE NEEDED BY EARLY AFTERNOON TO INCLUDE MUCH OF
   CENTRAL AND THE REMAINDER OF NORTHERN ALABAMA.
   
   AS WEAKENING MID-LEVEL CIRCULATION CONTINUES TO LIFT EAST NORTHEAST
   OF THE OZARK PLATEAU INTO THE LOWER OHIO VALLEY...THE TENDENCY WILL
   BE FOR ASSOCIATED STRONGER MID-LEVEL FORCING TO SPREAD ACROSS THE
   TENNESSEE VALLEY TOWARD THE SOUTHERN APPALACHIANS.  LOW-LEVEL
   ENVIRONMENT ACROSS NORTHWEST GEORGIA/NORTHEAST ALABAMA INTO EASTERN
   TENNESSEE REMAINS DRY...AND INCREASING PRECIPITATION NEXT FEW HOURS
   MAY MAINTAIN A STABLE BOUNDARY LAYER ACROSS THIS REGION.
   
   AT THE SAME TIME...A WARMING...SUBSIDENT MID-LEVEL REGIME MAY BECOME
   INCREASINGLY SUPPRESSIVE OF CONVECTIVE DEVELOPMENT TO THE WEST/SOUTH
   OF ONGOING NARROW FRONTAL SQUALL LINE...WHICH MODELS SUGGEST WILL
   ADVANCE INTO AREAS WEST OF FLORENCE AL/COLUMBUS MS BY 17-18Z.  RISK
   FOR LARGE HAIL/DAMAGING WIND GUSTS MAY BECOME THE MOST PROMINENT
   SEVERE THREAT WITH THIS LINE.
   
   LONGER TERM SEVERE THREAT WITH ISOLATED SUPERCELLULAR ACTIVITY IN
   WARM ADVECTION REGIME DOWNSTREAM OF SQUALL LINE IS MORE UNCERTAIN AS
   IT LIFTS EAST NORTHEAST OF FLORENCE/MUSCLE SHOALS...INTO A MORE
   STABLE BOUNDARY LAYER ACROSS SOUTHERN MIDDLE TENNESSEE THE NEXT FEW
   HOURS.  BUT...LATEST RUC GUIDANCE IS SUGGESTIVE THAT INHIBITION MAY
   BECOME WEAK ENOUGH WITH DAYTIME HEATING TO SUPPORT ADDITIONAL
   ISOLATED CONVECTIVE DEVELOPMENT ACROSS CENTRAL/NORTHERN ALABAMA BY
   18-19Z.  IF THIS OCCURS...DEEP LAYER SHEAR IN AN ENVIRONMENT WITH
   MIXED LAYER CAPE IN EXCESS OF 1000 J/KG WILL BE FAVORABLE FOR
   SUPERCELLS.  AND...LOW-LEVEL HODOGRAPHS BENEATH A 40-50 KT
   SOUTHWESTERLY LOW-LEVEL JET AXIS WILL BE LARGE AND SUPPORTIVE OF THE
   POTENTIAL FOR TORNADOES.
   
   ..KERR.. 05/08/2008
   
   
   ATTN...WFO...MRX...FFC...OHX...BMX...HUN...MEG...JAN...
   
   33119057 33578972 34318914 34828876 35038820 35368703
   35438582 35108477 34108474 33048533 32538616 32388733
   32358880 32549003 32859060 32929058 
   
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