Sep 7, 2012 1300 UTC Day 1 Convective Outlook
Updated: Fri Sep 7 12:48:29 UTC 2012
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20120907 1300 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20120907 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
20120907 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
20120907 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 071245
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0745 AM CDT FRI SEP 07 2012
   
   VALID 071300Z - 081200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER OH VALLEY INTO
   PORTIONS OF THE OZARK PLATEAU AND MID SOUTH...
   
   ...SYNOPSIS...
   
   THE EQUATORWARD DEVELOPMENT OF A MID TO UPPER-LEVEL JET STREAK FROM
   NRN PARTS OF BC/AB TOWARD THE UPPER MS VALLEY WILL RESULT IN THE
   AMPLIFICATION AND EWD TRANSLATION OF POSITIVELY-TILTED...DOWNSTREAM
   TROUGH CURRENTLY FROM CNTRL ONT INTO THE NRN INTERMOUNTAIN REGION. 
   BY 08/12Z THIS TROUGH WILL ASSUME A NEAR-NEUTRAL TILT...AND EXTEND
   FROM ERN ONT TO THE OZARK PLATEAU.  THIS PATTERN EVOLUTION WILL
   SUPPORT A BROAD ZONE OF INCREASING HEIGHT FALLS/DYNAMIC FORCING FOR
   ASCENT FROM THE UPPER MIDWEST AND MID MO VALLEY SPREADING EWD/SEWD
   THROUGH THE GREAT LAKES...OH AND MID MS RIVER VALLEYS.
   
   IN THE LOW LEVELS...SURFACE CYCLONE OVER CNTRL IA WILL DEVELOP ENEWD
   TO SWRN ONT BY 08/12Z WITH THE MOST SUBSTANTIAL DEEPENING OCCURRING
   TONIGHT ACROSS THE MID AND UPPER OH VALLEY.  A TRAILING COLD FRONT
   WILL ADVANCE SWD/SEWD THROUGH THE CNTRL PLAINS AND MID MS VALLEY
   WITH THIS FEATURE EXTENDING FROM THE SURFACE LOW SWWD THROUGH THE TN
   AND LOWER MS VALLEYS INTO CNTRL TX BY THE END OF THE PERIOD. 
   MEANWHILE...A DIFFUSE WARM FRONT NOW POSITIONED IN W-E FASHION OVER
   THE OH VALLEY WILL LIFT NWD IN ADVANCE OF MIGRATORY CYCLONE. 
   
   ...LOWER GREAT LAKES WWD/SWWD ACROSS THE OH VALLEY INTO THE OZARK
   PLATEAU AND MID-SOUTH THIS AFTERNOON THROUGH TONIGHT...
   
   EARLY MORNING SATELLITE-DERIVED PW IMAGERY AND 12Z SOUNDING DATA
   INDICATE THE PRESENCE OF A MOIST AIR MASS FROM THE OZARKS INTO LOWER
   MS VALLEY...CHARACTERIZED BY SURFACE DEWPOINTS IN THE LOWER
   60S-LOWER 70S AND PW VALUES OF 1.5-1.8 INCHES.  STRENGTHENING SWLY
   LOW-LEVEL FLOW WILL ENHANCE THE FLUX OF THIS MOIST AIR MASS THROUGH
   THE MID MS VALLEY INTO OH VALLEY...BENEATH A NARROW EML
   PLUME...CONTRIBUTING TO AFTERNOON MLCAPE VALUES APPROACHING
   1500-3500 J/KG ACROSS CNTRL AND SRN PORTIONS OF THE SLIGHT RISK
   AREA.  AT THE SAME TIME...THE OVERALL AMPLIFICATION OF THE
   LARGE-SCALE TROUGH /AND ITS PROGRESSION TOWARD A NEUTRAL TILT
   CONFIGURATION/ WILL RESULT IN AN INTENSIFYING DEEP-LAYER WIND FIELD
   DEVELOPING ACROSS THE WARM SECTOR...ESPECIALLY FROM LATER THIS
   AFTERNOON THROUGH TONIGHT.
   
   RECENT CONVECTION-ALLOWING AND MESOSCALE MODEL GUIDANCE APPEARS TO
   HAVE A REASONABLY GOOD HANDLE ON NOCTURNAL MCS OVER NRN IL.  THESE
   DATA SUGGEST THAT WHILE THE MCS MAY UNDERGO DECAY WHILE PROGRESSING
   ESEWD THIS MORNING...IT/S RESIDUAL COLD POOL MAY SERVE AS THE FOCUS
   FOR STORM REGENERATION BY AFTERNOON ACROSS PORTIONS OF IL/IND. 
   FARTHER W...LOW-LEVEL UPLIFT ALONG SYNOPTIC COLD FRONT AND
   INCREASING HEIGHT FALLS ALOFT WILL FOSTER AN INCREASE IN STORM
   COVERAGE AND VIGOR THROUGH THE AFTERNOON FROM THE OZARKS THROUGH MID
   MS VALLEY.  THE COMBINATION OF THE MODERATE INSTABILITY AND
   STRENGTHENING DEEP-LAYER SHEAR WILL SUPPORT BOTH LINEAR AND
   SUPERCELL CONVECTIVE MODES WITH THE PRIMARY HAZARDS BEING DAMAGING
   WINDS AND LARGE HAIL.  
   
   THE GREATEST RISK FOR A TORNADO OR TWO WILL EXIST WITHIN A COUPLE OF
   REGIMES WHERE LOW-LEVEL SHEAR WILL BE LOCALLY ENHANCED:  1) WITH ANY
   SUSTAINED STORMS DEVELOPING ALONG AND AHEAD OF SURFACE LOW
   TRACK...AND 2) IN ASSOCIATION WITH STORMS DEVELOPING ALONG COLD
   FRONT AND THEN FAVORABLY INTERACTING WITH OUTFLOW BOUNDARY TRAILING
   CURRENT IL MCS.
   
   A LOW PROBABILITY THREAT FOR DAMAGING WINDS AND PERHAPS A TORNADO
   WILL PERSIST THROUGH TONIGHT INTO EARLY SATURDAY FROM THE MID AND
   UPPER OH VALLEY INTO LOWER GREAT LAKES WHERE BOTH VERTICAL SHEAR AND
   FORCING FOR ASCENT WILL BE RAPIDLY INTENSIFYING.
   
   ...SRN PLAINS THIS AFTERNOON AND EVENING...
   
   A HOT...DEEPLY MIXED BOUNDARY LAYER WILL ONCE AGAIN DEVELOP BY
   AFTERNOON AHEAD OF COLD FRONT WHERE STEEP LOW TO MIDLEVEL LAPSE
   RATES WILL YIELD MLCAPE VALUES APPROACHING 500-1500 J/KG.  DESPITE
   THE PASSAGE OF STRONGER HEIGHT FALLS/FORCING FOR ASCENT TO THE
   NE...UPLIFT ALONG THE FRONT WILL GIVE RISE TO ISOLATED-WIDELY
   SCATTERED STORMS CAPABLE OF LOCALLY DAMAGING WIND GUSTS AND PERHAPS
   SOME HAIL THROUGH THIS EVENING.
   
   ..MEAD/MOSIER.. 09/07/2012
   
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