MESOSCALE DISCUSSION 0620 NWS STORM PREDICTION CENTER NORMAN OK 1045 AM CDT WED APR 27 2011 AREAS AFFECTED...FAR EASTERN LA AND NORTHERN/CENTRAL PORTIONS OF MS INTO AL CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY VALID 271545Z - 271715Z A LONG LEAD-TIME/LONG DURATION PARTICULARLY DANGEROUS /PDS/ TORNADO WATCH WILL LIKELY BE ISSUED SOON...MOST CERTAIN ACROSS NORTHERN/CENTRAL PORTIONS OF MS. VISIBLE SATELLITE/SURFACE OBSERVATIONAL TRENDS IMPLY RELATIVELY QUICK AIRMASS RECOVERY/DESTABILIZATION IS OCCURRING FROM LA INTO MS/AL THROUGH MID/LATE MORNING. THIS IS THE CASE NOT ONLY FOR IN THE VICINITY OF EARLY MORNING WEST-EAST OUTFLOW ACROSS MS/AL...WHERE SURFACE TEMPERATURES/DEWPOINTS HAVE EACH INCREASED 8-12F OVER THE PAST 2 HR...BUT ALSO IN THE WAKE OF AN APPARENT WAVE-LIKE FEATURE SPREADING EASTWARD CROSS CENTRAL PORTIONS OF MS/LA AS A CU FIELD OTHERWISE CONTINUES TO INCREASE/MATURE ACROSS NORTHEAST LA. AIDED BY STRONG AMPLIFICATION/INTENSIFICATION OF AN INCREASINGLY NEGATIVE TILT SHORTWAVE TROUGH/ASSOCIATED JET STREAK LATER TODAY...A VOLATILE SCENARIO IS EXPECTED TO UNFOLD THROUGH THE AFTERNOON. CONVECTIVE INITIATION OF VIGOROUS CONVECTION BY EARLY/MID AFTERNOON IS WELL SUPPORTED BY EXPERIMENTAL GUIDANCE SUCH AS SEVERAL RECENT HRRR RUNS AND THE 12Z WRF-NMM. SHORT TERM FORECAST SOUNDINGS FROM GUIDANCE SUCH AS THE RUC/12Z NAM...ACCENTUATED BY VERY LONG/STRONGLY CURVED LOW LEVEL HODOGRAPHS...SUPPORT THE NOTION OF SUPERCELLS CAPABLE OF STRONG/POTENTIALLY VIOLENT TORNADOES THIS AFTERNOON/EARLY EVENING ESPECIALLY ACROSS THE HIGH RISK AREA. ..GUYER.. 04/27/2011