DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0211 PM CDT WED APR 27 2011 VALID 272000Z - 281200Z ...THERE IS A HIGH RISK OF SVR TSTMS LATE THIS AFTN AND EVE ACROSS PARTS OF NORTHERN AND EASTERN MISSISSIPPI...CENTRAL AND NORTHERN ALABAMA...NORTHWEST GEORGIA AND SOUTHERN TENNESSEE... ...THERE IS A MDT RISK OF SVR TSTMS SURROUNDING THE HIGH RISK AREA....ACROSS MUCH OF THE REMAINDER OF MISSISSIPPI...ALABAMA AND NORTHERN GEORGIA...THE WESTERN CAROLINAS...TENNESSEE...KENTUCKY...SOUTHEASTERN INDIANA...OHIO...PARTS OF WESTERN PENNSYLVANIA AND WEST VIRGINIA... ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MODERATE RISK AREA...ACROSS MUCH OF THE EASTERN U.S.... ...20Z OUTLOOK UPDATE... ...A DANGEROUS OUTBREAK OF SEVERE THUNDERSTORM AND TORNADOES APPEARS UNDERWAY...AND CONFIDENCE IS INCREASING THAT THIS WILL EXPAND NORTHWARD FROM THE GULF STATES THROUGH MUCH OF THE OHIO VALLEY LATE THIS AFTERNOON AND EVENING... REMNANTS OF THE MORNING MESOSCALE CONVECTIVE SYSTEM AND ITS ASSOCIATED SURFACE COLD POOL...JUST EAST OF UPPER PORTIONS OF THE LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...REMAIN A COMPLICATING FACTOR CONCERNING CONVECTIVE POTENTIAL. HOWEVER... LATEST OBSERVATIONAL DATA SUGGEST THAT THE COLD POOL MAY BE IN THE PROCESS OF WEAKENING. AND BOUNDARY LAYER MOISTENING ASSOCIATED WITH THE PRECEDING RAINFALL...COUPLED WITH LATE AFTERNOON INSOLATION AND MODIFYING LOW-LEVEL THERMODYNAMIC PROFILES ASSOCIATED WITH STRONG DYNAMIC FORCING FOR UPWARD VERTICAL MOTION...PROBABLY WILL CONTRIBUTE TO SUFFICIENT DESTABILIZATION TO JUSTIFY EXPANDING MODERATE RISK SEVERE PROBABILITIES NORTHWESTWARD AND NORTHWARD THROUGH MUCH OF THE REMAINDER OF THE OHIO VALLEY. MODEL GUIDANCE...INCLUDING THE LATEST RUC AND 12Z ECMWF...INDICATE THAT A DEEP SURFACE CYCLONE WILL DEEPEN FURTHER AS IT MIGRATES NORTHWARD OUT OF THE OZARK PLATEAU...ACROSS THE LOWER OHIO VALLEY ...INTO THE LOWER GREAT LAKES REGION LATE THIS AFTERNOON AND TONIGHT. THIS WILL ACCOMPANY A VIGOROUS MID-LEVEL SHORT WAVE IMPULSE...WHICH IS PROGGED TO CONTRIBUTE TO STRONG MID-LEVEL HEIGHT FALLS CENTERED ALONG THE OHIO RIVER...FROM NEAR ITS CONFLUENCE WITH THE MISSISSIPPI RIVER INTO THE CINCINNATI OH AREA BETWEEN 28/00-06Z. A 50-70 KT 850 MB JET APPEAR LIKELY TO DEVELOP NORTHWARD TO THE WEST OF THE APPALACHIANS...AS A 100 KT 500 MB JET STREAK NOSES NORTHEASTWARD ACROSS KENTUCKY AND TENNESSEE INTO OHIO BY LATE THIS EVENING...CONTRIBUTING TO STRONG VERTICAL SHEAR SUPPORTIVE OF BOTH LONG-LIVED SUPERCELLS AND ORGANIZED STORM CLUSTERS. GIVEN AT LEAST WEAK BOUNDARY LAYER DESTABILIZATION... STRONG TORNADOES APPEAR POSSIBLE...IN ADDITION TO THE RISK FOR STRONG /STRAIGHT LINE/ DAMAGING CONVECTIVE GUSTS. ..KERR.. 04/27/2011