Apr 25, 2011 1300 UTC Day 1 Convective Outlook
Updated: Mon Apr 25 12:40:08 UTC 2011
Probabilistic to Categorical Outlook Conversion Table
Public Severe Weather Outlook

The SPC is forecasting ...severe thunderstorms expected over parts of the lower mississippi valley later today and tonight....   Please read the latest public statement about this event.

Categorical Graphic
20110425 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20110425 1300 UTC Day 1 Tornado Probabilities 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
20110425 1300 UTC Day 1 Damaging Wind Probabilities 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
20110425 1300 UTC Day 1 Large Hail Probabilities 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 251236
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0736 AM CDT MON APR 25 2011
   
   VALID 251300Z - 261200Z
   
   ...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT FROM
   NE TX/SE OK ACROSS CENTRAL/SRN AR...NW LA...NW MS...AND FAR WRN
   TN...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK
   AREA...FROM ERN TX/OK NEWD TO THE LOWER OH VALLEY...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON/EVENING FOR ERN
   OH AND PA...
   
   ...SYNOPSIS...
   A PRONOUNCED MIDLEVEL SHORTWAVE AND ASSOCIATED 70-80 KT MIDLEVEL JET
   OVER NM THIS MORNING WILL PROGRESS EWD OVER N TX/OK TODAY...AND NEWD
   OVER AR/MO TONIGHT.  AN ASSOCIATED SURFACE CYCLONE IS EXPECTED TO
   DEVELOP NEWD FROM S CENTRAL OK THIS MORNING TO SW MO THIS EVENING
   AND NW IL LATE TONIGHT.  A GRADUAL INCREASE IN THE WARM SECTOR
   SLY/SSWLY LLJ IS EXPECTED LATER TODAY INTO TONIGHT AS THE MIDLEVEL
   TROUGH EJECTS ENEWD AND THE SURFACE CYCLONE DEEPENS.  INCREASING
   VERTICAL SHEAR IN A MOIST/UNSTABLE WARM SECTOR WILL SUPPORT A RISK
   FOR SIGNIFICANT SEVERE STORMS TODAY INTO TONIGHT...THOUGH SEVERAL
   MESOSCALE FACTORS ADD UNCERTAINTY TO THE FORECAST.
   
   ...NE TX/SE OK ENEWD TO WRN TN/NW MS THROUGH TONIGHT...
   COMPLICATED SCENARIO IS ALREADY UNFOLDING THIS MORNING WITH THE
   WEAKENING COLD POOL FROM OVERNIGHT CONVECTION BEING OVERTAKEN BY
   ANOTHER MCS MOVING ALONG THE OUTFLOW BOUNDARY INTO SW AR.  THIS MCS
   WILL LIKELY PERSIST THROUGH MUCH OF THE DAY WHILE PROGRESSING ACROSS
   MUCH OF CENTRAL/SRN AR...GENERATING ANOTHER COLD POOL AND INHIBITING
   NWD PROGRESS OF THE WARM SECTOR IN AR.  THE MCS WILL INITIALLY POSE
   A THREAT FOR DAMAGING WINDS AND LARGE HAIL...THOUGH THERE IS SOME
   RISK FOR SUPERCELLS TO EVOLVE ON THE S/SW FLANK OF THE MCS AS THE
   BOUNDARY LAYER DESTABILIZES FROM NE TX INTO SRN AR.  FARTHER W IN
   N/NE TX AND SE OK...SOME NWD RECOVERY IS EXPECTED IN THE WAKE OF THE
   MORNING STORMS...AND IN ADVANCE OF THE SURFACE CYCLONE.  STRONG
   INSTABILITY /MLCAPE OF 2500-3500 J PER KG/ IS EXPECTED E/SE OF THE
   COLD FRONT/DRYLINE TRIPLE POINT IN N TX...AS A RESULT OF UPPER 60S
   BOUNDARY LAYER DEWPOINTS BENEATH 7-8 C/KM MIDLEVEL LAPSE RATES.
   
   ADDITIONAL SEVERE THUNDERSTORM DEVELOPMENT IS LIKELY BY EARLY-MID
   AFTERNOON NEAR THE TRIPLE POINT...WHERE THE STRONG INSTABILITY AND
   EFFECTIVE BULK SHEAR IN EXCESS OF 50 KT WILL FAVOR SUPERCELLS WITH
   VERY LARGE HAIL.  THE BOUNDARY LAYER WILL BE SUFFICIENTLY MOIST AND
   LOW-LEVEL SHEAR WILL BE SUFFICIENTLY STRONG /EFFECTIVE SRH OF
   250-350 M2 PER S2/ TO SUPPORT THE RISK FOR A FEW STRONG TORNADOES
   BEGINNING THIS AFTERNOON IN NE TX/SE OK...AND SPREADING INTO NW LA
   AND CENTRAL/SRN AR LATER THIS EVENING AND CONTINUING INTO TONIGHT.
   
   ...NRN AR/SRN MO/IL THROUGH TONIGHT...
   THE NRN EXTENT OF THE MORE SIGNIFICANT SEVERE THUNDERSTORM/TORNADO
   THREAT IS QUITE UNCERTAIN GIVEN THE STABILIZING IMPACTS OF ONGOING
   AND EXPECTED THUNDERSTORM CLUSTERS.  AT THIS TIME...IT APPEARS THAT
   THE NWD EXTENT OF THE STRONGER INSTABILITY WILL BE LIMITED BY
   MULTIPLE THUNDERSTORM CLUSTERS AND CONVECTIVE OUTFLOWS...SUCH THAT
   ONLY WEAK INSTABILITY IS LIKELY INVOF THE DEEPENING SURFACE CYCLONE
   THIS EVENING INTO TONIGHT.  DEEP-LAYER AND LOW-LEVEL VERTICAL SHEAR
   WILL BE SUFFICIENT FOR ORGANIZED SEVERE STORMS...BUT THE WEAK
   INSTABILITY AND WIDESPREAD CONVECTION FARTHER TO THE S WILL TEND TO
   LIMIT THE OVERALL DAMAGING WIND AND TORNADO RISK THIS FAR N.
   
   ...ERN OH/PA THIS AFTERNOON/EVENING...
   A LOW-AMPLITUDE SHORTWAVE TROUGH OVER THE LOWER OH RIVER THIS
   MORNING WILL EJECT ENEWD TOWARD NE OH/NW PA BY THIS EVENING...AND
   THIS WAVE WILL BE PRECEDED BY A WEAK SURFACE LOW ALONG A SLOW-MOVING
   WARM FRONT THAT WILL DRIFT NWD ACROSS PA TODAY.  THE FOCUS FOR
   THUNDERSTORM DEVELOPMENT WILL BE BETTER DEFINED ACROSS ERN OH/NW PA
   THIS AFTERNOON ALONG THE PATH OF THE WEAK WAVE...BUT THERE ARE SOME
   CONCERNS REGARDING THE MAGNITUDE OF THE INSTABILITY BASED ON
   LINGERING CLOUDS/RAIN.  FARTHER E IN PA...SOMEWHAT RICHER LOW-LEVEL
   MOISTURE AND STRONGER SURFACE HEATING ARE EXPECTED E OF THE
   MOUNTAINS.  HERE...THERE WILL BE NO CLEAR FOCUS FOR STORM
   DEVELOPMENT ASIDE FROM THE WARM FRONT.  IF STORMS DO FORM...VERTICAL
   SHEAR AND INSTABILITY COULD SUPPORT SUPERCELLS WITH DAMAGING WINDS
   AND SOME HAIL.
   
   ...TX PANHANDLE THIS AFTERNOON...
   THERE WILL BE A NARROW WINDOW OF OPPORTUNITY FOR SURFACE-BASED
   THUNDERSTORM DEVELOPMENT THIS AFTERNOON IN A NW-SE CORRIDOR ALONG
   THE COLD FRONT...WITH THE MIDLEVEL TROUGH OVERHEAD.  SURFACE HEATING
   AND 500 MB TEMPERATURES NEAR -20 C COULD SUPPORT
   HIGH-BASED/LOW-TOPPED STORMS ALONG THE FRONT.  GIVEN COLD
   TEMPERATURES ALOFT AND INVERTED-V PROFILES IN THE LOW LEVELS...HAIL
   AND STRONG OUTFLOW WINDS WILL BE POSSIBLE WITH MARGINAL
   SUPERCELL-TYPE STORMS.
   
   ..THOMPSON/COHEN.. 04/25/2011
   
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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z