MESOSCALE DISCUSSION 0640 NWS STORM PREDICTION CENTER NORMAN OK 0639 PM CDT WED APR 27 2011 AREAS AFFECTED...MUCH OF AL/NORTHWEST GA CONCERNING...TORNADO WATCH 235... VALID 272339Z - 280045Z THE SEVERE WEATHER THREAT FOR TORNADO WATCH 235 CONTINUES. PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCH 235 CONTINUES UNTIL 03Z. A HIGH-END TORNADO OUTBREAK WILL CONTINUE INTO THIS EVENING ACROSS A LARGE PART OF CENTRAL/NORTHEAST AL AND NORTHWEST GA. THIS IS AN EXTREMELY DANGEROUS AND LIFE-THREATENING SITUATION! CITIES AND AREAS AT GREATEST RISK INCLUDE BIRMINGHAM...THE I-59 CORRIDOR OF WESTERN/NORTHEAST AL...I-65 ACROSS NORTHERN/CENTRAL AL...AND I-20. 23Z SURFACE ANALYSIS CONTINUES TO REFLECT A HIGHLY FAVORABLE ENVIRONMENT FOR TORNADIC SUPERCELLS...WITH RELATIVELY STRONG SOUTHERLY LOW LEVEL WINDS COINCIDENT WITH NEAR 70F SURFACE DEWPOINTS ESPECIALLY WITHIN AN AXIS FROM EAST-CENTRAL MS INTO WEST-CENTRAL TO NORTHEAST AL/NORTHWEST GA. IN PROXIMITY TO DESTRUCTIVE TORNADIC SUPERCELL NEAR/NORTH OF BIRMINGHAM...WSR-88D VWP DATA NOW REFLECTS 0-1 KM SRH IN EXCESS OF 600 M2/S2. A SEMI-DISCRETE/SUSTAINED SUPERCELLULAR MODE...COINCIDENT WITH THE GREATEST INGREDIENTS FOR STRONG/VIOLENT TORNADOES...IS EXPECTED TO REMAIN ACROSS WEST-CENTRAL TO NORTHEAST/EAST-CENTRAL AL AND NORTHWEST GA THROUGH EARLY EVENING. A CORRIDOR OF ROUGHLY 50 MILES EITHER SIDE OF I-59...AS WELL AS THE GENERAL VICINITY OF I-20...REMAINS OF PARTICULARLY HIGH CONCERN FOR LONG-LIVED/DESTRUCTIVE TORNADIC SUPERCELLS. ANOTHER RELATIVELY CONCENTRATED AREA OF HIGH SHORT-TERM CONCERN WILL REMAIN ACROSS FAR NORTHERN AL IN VICINITY OF A RECOVERING OUTFLOW BOUNDARY...WHILE STORMS ALONG THE EASTWARD-ADVANCING PRE-FRONTAL TROUGH/DRYLINE OTHERWISE INCREASE AND GROW UPSCALE/MERGE WITH LEADING SEMI-DISCRETE STORMS. THIS MORE LINEAR EVOLUTION WILL LIKELY TEMPER THE HIGH-END TORNADO POTENTIAL WITH TIME ACROSS NORTHERN AL...BUT THE RISK FOR DAMAGING WINDS/ISOLATED TORNADOES WILL NONETHELESS PERSIST THIS EVENING. ..GUYER.. 04/27/2011