Sep 4, 2012 1300 UTC Day 1 Convective Outlook
Updated: Tue Sep 4 12:50:31 UTC 2012
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20120904 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20120904 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
20120904 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
20120904 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 041246
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0746 AM CDT TUE SEP 04 2012
   
   VALID 041300Z - 051200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL
   PLAINS...UPPER MS VALLEY AND WRN GREAT LAKES...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF NERN OH AND
   WRN PA/NY...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF THE NCNTRL
   GULF COAST...
   
   ...SYNOPSIS...
   BROADLY CYCLONIC MID LEVEL FLOW WILL STRENGTHEN FROM THE NRN PLAINS
   TO GREAT LAKES AS THE NEXT IN A SERIES OF SHORTWAVE TROUGHS ROTATES
   THROUGH THE BASE OF A LARGE UPPER LOW OVER CNTRL CANADA. THIS NEXT
   MID/UPPER WAVE WILL MOVE TOWARD THE DAKOTAS AND WRN MN THROUGH
   TONIGHT WITH A SHARPENING COLD FRONT SPREADING ACROSS THESE AREAS
   THROUGH WEDNESDAY MORNING. MEANWHILE...A LEADING LOWER AMPLITUDE
   IMPULSE...CURRENTLY MOVING EAST FROM SRN ONTARIO AND LOWER MI...WILL
   PRODUCE WEAK HEIGHT FALLS ACROSS THE ERN GREAT LAKES AND NEW
   ENGLAND. TO THE SOUTH OF THESE BETTER DEFINED DISTURBANCES...THE
   SUBTROPICAL RIDGE WILL BE SOMEWHAT SUPPRESSED OVER THE CNTRL/SRN
   PLAINS...THE INCREASINGLY FRAGMENTED REMNANT CIRCULATION FROM ISAAC
   WILL MOVE SOUTH ACROSS THE NCNTRL GULF COAST...AND A WEAK UPPER LOW
   OFF THE EAST COAST OF FL WILL REMAIN NEARLY STATIONARY.
   
   SFC FEATURES IN MOST AREAS ARE ILL-DEFINED AND SUBTLE. A BROAD WARM
   FRONTAL ZONE EXISTS OVER THE MID ATLANTIC REGION NWD TO NY AHEAD OF
   THE SFC TROUGH AXIS SUPPORTING ONGOING TSTMS FROM LOWER MI INTO
   ONTARIO. THIS SFC TROUGH EXTENDS W-SWWD TO MO/KS WHERE IT ALSO
   APPEARS TO BE SUPPORTING SCATTERED MORNING CONVECTION. A DECAYING
   MCS ACROSS AL HAS GENERATED A STABLE COLD POOL WITH AN OUTFLOW
   BOUNDARY NEAR THE MS BORDER. AND...A WEAK BUT COHERENT SFC LOW WAS
   LOCATED ALONG A SUBTLE SFC TROUGH OVER MN. THESE ARE THE PRIMARY
   FEATURES THAT SHOULD DRIVE AN INCREASE IN CONVECTIVE POTENTIAL
   THROUGH THE DAY TODAY.
   
   ...MN/WI/IA...
   STRONG DESTABILIZATION IS FORECAST TO OCCUR NEAR THE WEAK SFC LOW
   AND PRE-FRONTAL TROUGH AXIS FROM SERN MN INTO WRN WI BY AFTERNOON.
   CAPPING/INHIBITION IN THE AREA HAS DIMINISHED IN RECENT DAYS AS MID
   LEVEL TEMPERATURES HAVE COOLED. MEANWHILE...LOW LEVEL MOISTURE AND
   STEEPENING LAPSE RATES WILL CONTRIBUTE TO MLCAPE OF 2000-3000 J/KG
   BY AFTERNOON. STORMS FORMING NEAR THE LOW AND TROUGH WILL EXIST
   AMIDST SUFFICIENT SHEAR FOR PERSISTENCE AND ORGANIZATION WITH
   SUPERCELLS AND/OR EVOLVING LINE SEGMENTS POSSIBLE. MAGNITUDE OF
   INSTABILITY AND SHEAR ANTICIPATED COULD RESULT IN A COUPLE OF STORMS
   CAPABLE OF PRODUCING VERY LARGE HAIL. WIND DAMAGE POTENTIAL MAY
   INCREASE IF CONVECTION CAN GROW AND ORGANIZE INTO A SMALL FORWARD
   PROPAGATING MCS INTO THE EVENING. ADDITIONAL STRONG TO SEVERE STORMS
   ARE POSSIBLE OVERNIGHT AS THE COLD FRONT SURGES EAST FROM THE
   DAKOTAS INTO MN. DEGREE OF AVAILABLE INSTABILITY AHEAD OF THE FRONT
   WILL BE MODULATED BY PRIOR CONVECTIVE DEVELOPMENT AND COVERAGE.
   GIVEN UNCERTAINTIES AND TIMING OF THE FRONTAL ADVANCE...PORTIONS OF
   THE ERN DAKOTAS AND WRN MN WILL REMAIN IN LOWER SEVERE PROBABILITIES
   FOR NOW.
   
   A SEPARATE AREA OF SEVERE STORM DEVELOPMENT POTENTIAL IS INDICATED
   IN LATEST GUIDANCE ALONG THE TROUGH/THERMAL AXIS FROM ERN NEB INTO
   IA. CAPPING WILL BE MORE SUBSTANTIAL IN THESE AREAS BUT PERSISTENT
   WARM ADVECTION AND BOUNDARY LAYER HEATING MAY PROVE ADEQUATE FOR
   STORM INITIATION LATE IN THE AFTERNOON OR BY EARLY EVENING. THIS
   DEVELOPMENT WILL OCCUR COINCIDENT WITH AN INCREASE IN WLY MID LEVEL
   FLOW SUFFICIENT FOR STORM ORGANIZATION WITH SOME CHANCE FOR BOTH
   LARGE HAIL AND LOCALLY DAMAGING WINDS.
   
   ...OH/PA/NY...
   HAVE ADDED A SLGT RISK TO THESE AREAS GIVEN CURRENT CONVECTIVE
   TRENDS FROM LOWER MI TO THE ERN GREAT LAKES. LOW LEVEL MOISTURE HAS
   INCREASED AHEAD OF THE ADVANCING TROUGH THAT IS DRIVING CURRENT
   STORMS WITH DEWPOINTS NOW NEARING 70F FROM NERN OH TO WRN NY.
   SATELLITE IMAGERY DOES DEPICT AN INCREASE IN LOW CLOUDS THIS MORNING
   BUT AT LEAST SOME DIURNAL DESTABILIZATION APPEARS LIKELY WITH MLCAPE
   REACHING 1000 J/KG IN SOME AREAS...PERHAPS LOCALLY HIGHER WHERE
   GREATER INSOLATION OCCURS. AS LIFT ASSOCIATED WITH THE SFC AND UPPER
   TROUGHS SPREADS EAST THROUGH THE DAY STORMS ARE EXPECTED TO INCREASE
   IN COVERAGE ACROSS THE SLGT RISK AREA. EFFECTIVE BULK SHEAR ALSO
   STRENGTHENS TO AROUND 30KT AND EXPECT NUMEROUS MARGINALLY ORGANIZED
   MULTICELL STORMS POSING A THREAT OF DOWNBURST WINDS.
   
   ...NCNTRL GULF COAST...
   LATENT HEAT RELEASE FROM REPEAT DEEP CONVECTION APPEARS TO HAVE
   ENHANCED MID LEVEL CIRCULATION ACROSS SRN AL THIS MORNING WITH
   POSSIBLE MCV EVOLVING COINCIDENT WITH THE REMNANT CIRCULATION FROM
   ISAAC. STORM-SCALE AND NAM GUIDANCE ARE IN REASONABLE AGREEMENT AND
   INDICATE THAT AREAS ON THE WRN FLANK OF THE ONGOING
   CONVECTION...FROM MS/AL BORDER WWD ACROSS MS TO ERN LA...WILL BECOME
   STRONGLY UNSTABLE WITH HEATING OF THE DAY. THIS SEEMS REASONABLE
   BASED ON LATEST SATELLITE IMAGERY DEPICTING ONLY THIN SCATTERED
   CLOUDS ACROSS THESE AREAS WHERE SFC DEWPOINTS ARE IN THE MID 70S F.
   WIND PROFILES ACROSS THE REGION REMAIN CHARACTERIZED BY WEAK LOW
   LEVEL W-SWLYS TOPPED BY MODEST NLY FLOW IN THE MID LEVELS. THE
   VEERED WIND PROFILES SHOULD CONTRIBUTE TO STORM ORGANIZATION AND
   POSSIBLY SOME UPSCALE GROWTH WITH SWD/SWWD CELL PROPAGATION AND AN
   INCREASE IN DAMAGING WIND HAZARD INTO THIS AFTERNOON.
   
   ..CARBIN/ROGERS.. 09/04/2012
   
   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z