MESOSCALE DISCUSSION 0636 NWS STORM PREDICTION CENTER NORMAN OK 0538 PM CDT WED APR 27 2011 AREAS AFFECTED...MIDDLE/EASTERN TN TO FAR WESTERN NC CONCERNING...TORNADO WATCH 238... VALID 272238Z - 280015Z THE SEVERE WEATHER THREAT FOR TORNADO WATCH 238 CONTINUES. PARTICULARLY DANGEROUS SITUATION /PDS/ TORNADO WATCH 238 CONTINUES UNTIL 05Z ACROSS MIDDLE/EASTERN TN. THE POTENTIAL FOR TORNADOES...INCLUDING STRONG TORNADOES...WILL ONLY INCREASE THROUGH EARLY/MID EVENING. THE RELATIVELY HIGHEST TORNADIC POTENTIAL INVOLVES SOUTHERN MIDDLE TN/SOUTHEAST TN INCLUDING THE CHATTANOOGA VICINITY AND I-24/I-75 CORRIDORS. A COMPLEX CONVECTIVE MODE INCLUDING EMBEDDED TORNADIC SUPERCELLS CONTINUE TO DEVELOP/QUICKLY SPREAD NORTHEASTWARD ACROSS PDS TORNADO WATCH 238. OF CONCERN...THE AIRMASS ALONG A PRIOR OUTFLOW BOUNDARY ALONG THE TN/AL BORDER CONTINUES TO RECOVER...WITH A CONTINUED LIKELY NORTHWARD ADVANCEMENT INTO THE SOUTHERN PART OF MIDDLE TN AS WELL AS MUCH OF EASTERN TN THIS EVENING. ACCORDINGLY...RICHER LOW LEVEL MOISTURE /LOWER-MIDDLE 60S F SURFACE DEWPOINTS/ WILL CONTINUE TO SURGE NORTH-NORTHEASTWARD...HEIGHTENING TORNADO POTENTIAL ESPECIALLY ACROSS SOUTHEAST TN. ADDITIONALLY...RAPID AIRMASS RECOVERY/DESTABILIZATION CONTINUES TO OCCUR UPSTREAM ACROSS WESTERN TN BENEATH THE MID LEVEL DRYSLOT...AND THIS WILL FURTHER AID DESTABILIZATION INTO MIDDLE TN THIS EVENING. WITH SUPERCELLS REMAINING LIKELY INTO THIS EVENING...EXTREME SHEAR/LOW LEVEL SHR WILL BE HIGHLY FAVORABLE FOR TORNADIC SUPERCELLS...INCLUDING THE POSSIBILITY OF STRONG TORNADOES. ..GUYER.. 04/27/2011