Apr 27, 2011 2000 UTC Day 1 Convective Outlook | |
Updated: Wed Apr 27 19:16:08 UTC 2011 | |
Probabilistic to Categorical Outlook Conversion Table | |
Public Severe Weather Outlook | |
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The SPC is forecasting ...outbreak of tornadoes and severe thunderstorms expected over parts of the tennessee valley...southern appalachian mountains and southern ohio valley this afternoon through tonight.... Please read the latest public statement about this event. |
Categorical Graphic |
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Probabilistic Tornado Graphic |
Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point. |
Probabilistic Damaging Wind Graphic |
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point. |
Probabilistic Large Hail Graphic |
Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point. |
SPC AC 271911 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 .PREV DISCUSSION... /ISSUED 1129 AM CDT WED APR 27 2011/ ...MAJOR TORNADO OUTBREAK EXPECTED THIS AFTERNOON AND EVENING ACROSS THE TN VALLEY AND SRN APPALACHIAN MTNS EXTENDING NWD INTO THE SRN OH VALLEY... ...TN VALLEY/SRN APPALACHIAN MTNS AND SRN OH VALLEY... A VIGOROUS UPPER-LEVEL TROUGH WILL MOVE INTO THE OZARKS TODAY AS A POWERFUL MID-LEVEL JET ROUNDS THE BASE OF THE TROUGH AND NOSES INTO THE OH AND TN VALLEYS. AT THE SFC... A LOW WILL MOVE QUICKLY NEWD ACROSS THE MID-MS VALLEY AS LOW-LEVEL MOISTURE IS TRANSPORTED NNEWD ACROSS THE OH AND TN VALLEYS THIS AFTERNOON. MODERATE DESTABILIZATION IS ALREADY IN PLACE ACROSS THE LOWER MS VALLEY AND THIS AIR MASS SHOULD MOVE NEWD INTO THE MODERATE AND HIGH RISK AREAS BY LATE THIS AFTERNOON. THE WARM AND MOIST AIR MASS ALONG WITH STRONG SHEAR PROFILES IN THE LOW TO MID-LEVELS WILL BE VERY FAVORABLE FOR SEVERE THUNDERSTORMS AND TORNADOES THIS AFTERNOON AND EVENING. THIS SYSTEM IS VERY ORGANIZED AND CONFIDENCE IS HIGH REGARDING THE POTENTIAL FOR A MAJOR TORNADO OUTBREAK THIS AFTERNOON AND EVENING ACROSS THE CNTRL GULF COAST STATES AND TN VALLEY EXTENDING NWD INTO THE SRN OH VALLEY. CONCERNING THE CURRENT SETUP...A LARGE MCS IS ONGOING ACROSS THE TN VALLEY. THIS CONVECTIVE SYSTEM IS TIMED TO MOVE INTO ERN TN AND NW GA BY 21Z. MESOANALYSIS SHOWS A RESERVOIR OF MODERATE INSTABILITY FROM LA EXTENDING EWD ACROSS SCNTRL MS WHERE MLCAPE VALUES ARE ESTIMATED IN THE 2000 TO 3000 J/KG RANGE. THIS MODERATE INSTABILITY SHOULD BE TRANSPORTED NEWD INTO THE HIGH RISK AREA THIS AFTERNOON AS THE MCS EXITS THE REGION TO THE EAST. AS THE THERMODYNAMIC SETUP IMPROVES...THE WIND SHEAR ENVIRONMENT WILL ALSO RAPIDLY BECOME MORE FAVORABLE AS THE NOSE OF A 80 TO 100 KT MID-LEVEL JET EJECTS EWD ACROSS THE REGION AND INTERACTS WITH A WELL-DEVELOPED LOW-LEVEL JET. THIS WILL CREATE LARGE LOOPING HODOGRAPHS FROM ERN MS AND NCNTRL AL NWD INTO SRN TN. 0-3 KM STORM RELATIVE HELICITIES IN THE 450 TO 600 M2/S2 RANGE SHOULD BE VERY FAVORABLE FOR TORNADIC SUPERCELLS. THE CURRENT THINKING IS THAT THE GREATEST TORNADO POTENTIAL WILL EXIST LATE THIS AFTERNOON AND EARLY THIS EVENING FROM COLUMBUS MS EWD TO BIRMINGHAM AND HUNTSVILLE AL. THIS AREA IS CURRENTLY SOUTH OF THE ONGOING MCS WHERE DESTABILIZATION SHOULD BE MOST FAVORABLE. AS SUPERCELLS INITIATE IN ERN MS AND TRACK ENEWD ACROSS THE HIGH RISK AREA LATE THIS AFTERNOON...A TORNADO OUTBREAK IS EXPECTED. A FEW LONG-TRACK STRONG TORNADOES AND POSSIBLY A VIOLENT TORNADO OR TWO MAY OCCUR AS THE LOW-LEVEL JET STRENGTHENS EARLY THIS EVENING. HAVE ADDED A 45 PERCENT SIG-TOR AREA WHERE CONFIDENCE IS THE HIGHEST CONCERNING THE POTENTIAL FOR LONG-TRACK TORNADOES. LARGE HAIL AND WIND DAMAGE WILL ALSO BE LIKELY WITH SUPERCELLS THAT DEVELOP. FURTHER TO THE NORTH ACROSS MIDDLE TN IN WCNTRL KY...THE ONGOING MCS IS HAMPERING DESTABILIZATION. HOWEVER...AS THE MID-LEVEL JET NOSES INTO THE REGION FROM THE WEST...THE MODERATE INSTABILITY IN NRN LA AND SRN AR IS EXPECTED TO ADVECT QUICKLY NNEWD ACROSS WCNTRL TN AND WCNTRL KY BETWEEN THE EXITING MCS AND A CLUSTER OF STORMS IN NW AR AND SRN MO. THIS SHOULD ALLOW THE MOIST AXIS TO BE LOCATED FROM WEST OF NASHVILLE NEWD TO NEAR LOUISVILLE WHERE NUMEROUS SFC-BASED THUNDERSTORMS ARE EXPECTED TO INITIATE LATE THIS AFTERNOON. THE LOW-LEVEL JET AND MID-LEVEL JET ARE FORECAST TO BE JUXTAPOSED ACROSS THIS CORRIDOR SUGGESTING SHEAR PROFILES WILL BE VERY FAVORABLE FOR SUPERCELLS AND TORNADOES EVEN IF DESTABILIZATION IS NOT AS GREAT AS IS EXPECTED. THE CURRENT THINKING IS THAT A BROKEN LINE OF TORNADIC SUPERCELLS WILL INITIATE ALONG THE WRN EDGE OF THE MODERATE RISK AREA AND TRACK EWD ACROSS CNTRL KY AND MIDDLE TN EARLY THIS EVENING. THE LOW-LEVEL SHEAR ENVIRONMENT WILL BE VERY FAVORABLE FOR TORNADOES AND A FEW LONG-TRACK STRONG TORNADOES MAY OCCUR. THE MODERATE RISK AREA HAS BEEN EXTENDED WWD ACROSS PARTS OF MIDDLE TN AND CNTRL KY TO ACCOUNT FOR THIS POSSIBILITY. LARGE HAIL AND WIND DAMAGE WILL ALSO BE POSSIBLE WITH SUPERCELLS THAT DEVELOP. AS A BROKEN LINE OF TORNADIC SUPERCELLS MOVES EWD ACROSS THE HIGH AND MODERATE RISK AREAS THIS EVENING...A TRANSITION TO MORE OF A WIND DAMAGE THREAT MAY OCCUR AS THE LINE CONGEALS AND BOWING LINE-SEGMENTS DEVELOP. AN ENHANCED WIND DAMAGE THREAT SHOULD EXIST AS FAR EAST AS WRN VA ...WRN NC AND WRN SC DURING THE LATE EVENING HOURS WHEN A LARGE MCS MOVES INTO THE SRN APPALACHIAN MTNS. THE TORNADO THREAT MAY SHIFT SWD LATE THIS EVENING INTO NRN GA WHERE THE STORMS MAY TEND TO REMAIN DISCRETE. ...CNTRL TO NRN APPALACHIAN MTNS/CAROLINAS/ERN GULF COAST STATES... THE UPPER-LEVEL TROUGH OVER THE CNTRL STATES WILL MOVE INTO THE MS VALLEY THIS EVENING AS A POWERFUL MID-LEVEL JET EJECTS NEWD OUT OF THE BASE OF THE TROUGH. THE EXIT REGION OF THE MID-LEVEL JET WILL MOVE INTO THE CNTRL APPALACHIAN MTNS AND ERN GREAT LAKES WHERE DEEP LAYER SHEAR PROFILES WILL BECOME MORE FAVORABLE FOR SEVERE STORMS TONIGHT. ALONG AND TO THE EAST OF THE JET AXIS...A LINE OF STRONG THUNDERSTORMS IS EXPECTED TO BE LOCATED FROM ERN OH EXTENDING SWD INTO FAR WRN SC AROUND 06Z. THIS LINE SHOULD MOVE EWD ACROSS NY...PA...VA...NC AND SC WHERE A WIND DAMAGE THREAT SHOULD EXIST DUE TO STRONG LOW-LEVEL FLOW. AN ENHANCED WIND DAMAGE THREAT COULD EXIST ACROSS VA AND WRN CAROLINAS WHERE THE MODELS DEVELOP MODERATE INSTABILITY AFTER 06Z. 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