Apr 23, 2011 2000 UTC Day 1 Convective Outlook
Updated: Sat Apr 23 20:01:08 UTC 2011
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20110423 2000 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20110423 2000 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
20110423 2000 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
20110423 2000 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 231957
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0257 PM CDT SAT APR 23 2011
   
   VALID 232000Z - 241200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SRN PLAINS TO THE
   CENTRAL APPALACHIANS...
   
   ...OH VALLEY...
   EARLY-MID AFTERNOON OBJECTIVE ANALYSES INDICATED DESTABILIZATION
   DOWNSTREAM OF ONGOING TSTM COMPLEX OVER NRN KY/SWRN OH. 
   MARGINAL-MODERATE INSTABILITY COMBINED WITH EFFECTIVE BULK SHEAR
   40-50 KT AND EFFECTIVE SRH 100-300 M2/S2 ARE EXPECTED TO SUPPORT AND
   MAINTAIN ORGANIZATION AS THIS ACTIVITY ADVANCES EWD.  GIVEN THESE
   TRENDS...THE SLIGHT RISK AND SEVERE PROBABILITIES HAVE BEEN EXPANDED
   NWD ACROSS MORE OF SRN OH AND EWD THROUGH ERN KY INTO CENTRAL WV FOR
   PRIMARILY DAMAGING WINDS AND TORNADO THREATS.  THE 5% TORNADO
   PROBABILITY HAS ALSO BEEN EXPANDED SWD ACROSS MORE OF SRN KY FOR
   SIMILAR TRENDS.
   
   ...NRN TX...
   19Z SURFACE ANALYSIS SHOWED AN AREA OF LOW PRESSURE LOCATED OVER WRN
   N TX...APPROXIMATELY 45 NW MWL...AND A FRONT EXTENDING ENEWD THROUGH
   FAR SOUTH CENTRAL OK TO WEST CENTRAL-NERN AR.  VERY STRONG
   INSTABILITY HAS DEVELOPED WITHIN THE WARM SECTOR NWD INTO NRN TX
   WITH MLCAPE 2000-3000 J/KG.  GIVEN THIS INSTABILITY...STEEP LAPSE
   RATES AND EFFECTIVE BULK SHEAR IN EXCESS OF 45 KT INVOF THE SURFACE
   LOW AND BOUNDARY SUPPORTS A WWD EXPANSION OF THE 5% TORNADO AND 15%
   DAMAGING WIND LINES...AND A NWD EXPANSION OF THE 10% SIGNIFICANT
   HAIL THREAT.
   
   ...PART OF NERN OK INTO SWRN MO...
   SLIGHT RISK HAS BEEN EXPANDED NWD INTO THIS REGION TO SUPPORT MAINLY
   A THREAT FOR SEVERE HAIL...GIVEN ONGOING TSTM DEVELOPMENT PER
   REGIONAL RADAR IMAGERY.  EFFECTIVE BULK SHEAR UP TO 50 KT WILL
   SUPPORT STORM ORGANIZATION...THOUGH MARGINAL INSTABILITY MAY LIMIT
   OVERALL SEVERE COVERAGE.
   
   ..PETERS.. 04/23/2011
   
   .PREV DISCUSSION... /ISSUED 1122 AM CDT SAT APR 23 2011/
   
   TODAYS UPPER PATTERN IS DOMINATED BY A LONG FETCH OF SOUTHWEST FLOW
   ALOFT FROM THE SOUTHWEST STATES INTO THE NORTHEAST.  A STRONG
   MID/UPPER LEVEL JET OVER THE GREAT LAKES REGION WILL MOVE INTO
   QUEBEC...LEAVING MUCH OF THE CENTRAL/EASTERN STATES WITH RATHER WEAK
   FORCING MECHANISMS ALOFT FOR ORGANIZED CONVECTIVE DEVELOPMENT. 
   NEVERTHELESS...A SURFACE FRONT EXTENDING FROM TX INTO THE UPPER OH
   VALLEY WILL PROVIDE THE FOCUS FOR THUNDERSTORMS TODAY AND TONIGHT.
   
   ...OH VALLEY...
   LATEST SURFACE ANALYSIS SHOWS THE MAIN SURFACE BAROCLINIC ZONE
   EXTENDING FROM NORTHERN AR NORTHEASTWARD ALONG THE OH RIVER INTO
   SOUTHERN OH.  SCATTERED SHOWERS AND THUNDERSTORMS HAVE BEEN ONGOING
   ALONG THIS AXIS OVERNIGHT...REINFORCING THE THERMAL/INSTABILITY
   GRADIENT.  RELATIVELY STRONG HEATING IS EXPECTED SOUTH OF THE
   BOUNDARY WHERE FORECAST SOUNDINGS SHOW MLCAPE VALUES AROUND 1500
   J/KG.  THE COMBINATION OF LOW LEVEL CONVERGENCE ALONG THE BOUNDARY
   AND A WEAK CAP TO ITS SOUTH WILL LEAD TO SCATTERED AFTERNOON STORMS.
    STEEP MID LEVEL LAPSE RATES AND EFFECTIVE DEEP-LAYER SHEAR OVER 40
   KNOTS WILL PROMOTE SUPERCELL STRUCTURES WITH LARGE HAIL AND DAMAGING
   WINDS THE MAIN THREATS.  LOW LEVEL SHEAR PROFILES ALSO SUPPORT SOME
   RISK OF TORNADOES THIS AFTERNOON AND EVENING.
   
   ...TX/OK/AR...
   A COLD FRONT IS SAGGING SLOWLY SOUTHWARD ACROSS OK AND NORTHWEST AR.
    THIS BOUNDARY SHOULD STALL BY EARLY AFTERNOON...WITH STRONG HEATING
   AND VERY UNSTABLE CONDITIONS DEVELOPING OVER SOUTHEAST OK/NORTHEAST
   TX AND PORTIONS OF WESTERN AR.  PRESENT INDICATIONS ARE THAT STORMS
   WILL DEVELOP RAPIDLY ALONG THE BOUNDARY BY LATE AFTERNOON AND SPREAD
   SOUTHEASTWARD INTO TX/AR THROUGH THE EVENING.  FORECAST SOUNDINGS
   SHOW AMPLE MOISTURE/CAPE AND BULK SHEAR VALUES OF 35-40
   KNOTS...FAVORABLE FOR SUPERCELLS.  THERMODYNAMIC PARAMETERS SUPPORT
   A RISK OF VERY LARGE HAIL ALONG AN AXIS FROM SOUTHEAST OK/NORTH
   CENTRAL TX INTO CENTRAL AR THIS AFTERNOON AND EVENING.
   
   LATER TONIGHT...LOW LEVEL WARM ADVECTION IS EXPECTED TO INTENSIFY
   ACROSS OK WHERE STEEP LAPSE RATES AND MODERATE ELEVATED CAPE WILL BE
   PRESENT.  SOME POTENTIAL FOR ELEVATED HAILSTORMS WILL EXIST TONIGHT
   ACROSS THIS REGION.
   
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