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Mesoscale Discussion 634
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   MESOSCALE DISCUSSION 0634
   NWS STORM PREDICTION CENTER NORMAN OK
   0501 PM CDT WED APR 27 2011
   
   AREAS AFFECTED...MUCH OF MS/AL TO NORTHWEST GA
   
   CONCERNING...TORNADO WATCH 232...235...
   
   VALID 272201Z - 272330Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 232...235...CONTINUES.
   
   PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCHES 232/235
   CONTINUE UNTIL 00Z/03Z RESPECTIVELY.
   
   A TORNADO OUTBREAK WILL CONTINUE INTO THIS EVENING ACROSS MUCH OF
   MS/AL INTO NORTHWEST GA. THIS IS AN EXTREMELY
   DANGEROUS/LIFE-THREATENING SITUATION! CITIES AND AREAS AT GREATEST
   RISK INCLUDE BIRMINGHAM...HUNTSVILLE...THE I-59 CORRIDOR OF NORTHERN
   AL...AND I-65 NEAR/NORTH OF BIRMINGHAM.
   
   A NUMBER OF SEMI-DISCRETE/LONG-LIVED TORNADIC SUPERCELLS CONTINUE TO
   FORM WITHIN A PRE-DRYLINE/PRE-COLD FRONTAL WARM SECTOR FROM
   SOUTH-CENTRAL MS NORTHEASTWARD INTO MUCH OF NORTHERN AL. OTHER
   TORNADIC STORMS CONTINUE TO INTERACT WITH A MODIFYING EFFECTIVE WARM
   FRONTAL-TYPE BOUNDARY ACROSS FAR NORTHERN AL IN THE GENERAL
   VICINITIES OF DECATUR/HUNTSVILLE.
   
   THE SPATIALLY WIDE WARM SECTOR IS VERY UNSTABLE AMID MIDDLE-UPPER
   60S F SURFACE DEWPOINTS...WITH LOWER 70S F SURFACE DEWPOINTS ACROSS
   PORTIONS OF SOUTHERN/MS. MLCAPE VALUES ARE AS HIGH AS 2000-4000 J/KG
   WITHIN THE WEAKLY CAPPED WARM SECTOR.
   
   RECENT REGIONAL WSR-88D VWP DATA IS INDICATIVE OF AN INCREASE IN LOW
   LEVEL WIND SPEEDS/HODOGRAPH CURVATURE OVER THE PAST FEW HOURS...WITH
   0-1 KM SRH VALUES NOW ESTIMATED TO BE IN EXCESS OF 300-400 M2/S2 AND
   0-3 KM SRH IN EXCESS OF 600 M2/S2 PER BIRMINGHAM/HUNTSVILLE WSR-88D
   VWPS. THIS WILL REMAIN HIGHLY FAVORABLE FOR LONG-LIVED
   STRONG/POTENTIALLY VIOLENT TORNADOES WITH ANY SUSTAINED SUPERCELLS
   WITHIN THE BROAD/VOLATILE WARM SECTOR INTO THIS EVENING.
   
   WHILE STRONG TORNADOES WILL BE POSSIBLE WITH ANY SUSTAINED
   SUPERCELLS WITHIN PDS TORNADO WATCH 232/235...THE RELATIVELY HIGHEST
   CONCERN OVER THE NEXT FEW HOURS WOULD APPEAR TO BE ACROSS
   WEST-CENTRAL AL AND NORTHERN HALF OF AL INTO FAR NORTHWEST GA.
   HERE...IN ADDITION TO THE AFOREMENTIONED RESIDUAL SURFACE
   BOUNDARY...RELATIVELY STRONG/BACKED LOW LEVEL FLOW IS EVIDENT IN 21Z
   SUBJECTIVE ANALYSIS AMID A RELATIVE MAXIMA OF 2-HR PRESSURE
   FALLS...ESPECIALLY ALONG/NORTH OF I-20 IN NORTHERN AL.
   
   ..GUYER.. 04/27/2011
   
   
   ATTN...WFO...FFC...BMX...HUN...MOB...MEG...JAN...
   
   LAT...LON   32559038 34728873 34398454 31278702 31499023 32559038 
   
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Page last modified: April 27, 2011
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