Sep 7, 2012 0600 UTC Day 1 Convective Outlook
Updated: Fri Sep 7 06:03:31 UTC 2012
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20120907 1200 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20120907 1200 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 1200 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 1200 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 070600
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0100 AM CDT FRI SEP 07 2012
   
   VALID 071200Z - 081200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS PORTIONS SERN LOWER MI/OH TO
   OZARKS AND MID-SOUTH......
   
   ...SYNOPSIS...
   DOMINANT UPPER-AIR FEATURE FOR THIS FCST WILL BE STG SHORTWAVE
   TROUGH -- NOW VERY POSITIVELY TILTED FROM NWRN ONT WSWWD ACROSS SRN
   MB...MT AND CENTRAL ID.  AS HEIGHTS RISE ACROSS MOST OF
   INTERMOUNTAIN W...500-MB TROUGH WILL TRANSLATE SEWD WITH ITS ERN
   PORTION INTENSIFYING.  BY 8/00Z...TROUGH SHOULD EXTEND FROM NRN ONT
   SWWD ACROSS LS...THROUGH PRIMARY VORTICITY FIELD OVER WI...ACROSS
   IA...TO SWRN NEB/NWRN KS REGION.  PERTURBATION WILL DEEPEN FURTHER
   AND BECOME LESS POSITIVELY TILTED WITH TIME...SUCH THAT BY
   8/12Z...VORTICITY CENTER SHOULD ARRIVE AT NRN INDIANA...WITH TROUGH
   ARCHING SWD/SWWD OVER SERN INDIANA...SERN MO AND NRN OK.
   
   RELATED SFC COLD FRONT AT START OF PERIOD SHOULD EXTEND SWWD FROM
   FRONTAL-WAVE LOW OVER SRN IA THROUGH CENTRAL/SWRN KS TO NERN NM.  AS
   LOW MOVES EWD TO NRN INDIANA BY 8/00Z...COLD FRONT SHOULD REACH SERN
   PORTIONS MO/OK/NM...WHILE WARM FRONT EXTENDS E OF LOW INVOF MI/OH
   BORDER AND LE.  OVERNIGHT...COLD FRONT WILL SWEEP SEWD TO S TX...WRN
   LA...MID TN...AND OH...CONNECTING WITH DEEPENING SFC CYCLONE OVER
   SRN ONT BY 12Z.
   
   ...DIURNAL...LOWER MI AND INDIANA TO OZARKS AND OK...
   STRENGTHENING COLD FRONT IS EXPECTED TO MOVE SEWD INTO PROGRESSIVELY
   HIGHER-THETAE AIR MASS DURING DAY...WHILE DIABATIC SFC HEATING
   BOOSTS BUOYANCY AND REDUCES CINH.  NET RESULT SHOULD BE DEVELOPMENT
   OF SCATTERED TSTMS INVOF FRONT DURING AFTERNOON...BUILDING NEWD AND
   SWWD WITH TIME INTO LENGTHY BAND OF SCATTERED-NUMEROUS STG-SVR
   TSTMS.  MAIN THREAT WILL BE DAMAGING GUSTS...ALTHOUGH LOW-LEVEL AND
   DEEP SHEAR WILL SUPPORT SUPERCELL POTENTIAL GENERALLY N OF OH RIVER
   AND E OF MS RIVER FOR LOCALLY ENHANCED HAIL THREAT AND CONDITIONAL
   TORNADO POTENTIAL.  LARGEST HODOGRAPHS SHOULD BE INVOF WARM FRONT
   DURING AFTERNOON...THEN AS LLJ STRENGTHENS FROM ABOUT 00Z
   ONWARD...IN SW-NE CORRIDOR ACROSS PORTIONS KY...INDIANA AND OH.  SFC
   DEW POINTS UPPER 60S TO LOW 70S F ALREADY ARE IN PLACE ACROSS BROAD
   AREA OF MID-SOUTH AND OH VALLEY REGIONS.  RELATED LOW-LEVEL MOISTURE
   WILL BE ADVECTED/TRANSPORTED POLEWARD AND AGAINST SFC WARM FRONT BY
   MID-LATE AFTERNOON.  ACCORDINGLY MODIFIED MODEL SOUNDINGS YIELD
   2500-3500 J/KG MLCAPE WITH LOCALLY HIGHER VALUES AHEAD OF COLD
   FRONT.
   
   EXAMINING AREAS SWWD FROM CATEGORICAL OUTLOOK AREA ACROSS
   OK...PREFRONTAL AIR MASS WILL BE CHARACTERIZED BY HOTTER AND MORE
   DEEPLY MIXED BOUNDARY LAYER.  COMPARED TO FARTHER NE...EXPECT LESS
   MOISTURE...LOWER MLCAPE...AND MORE VEERED SFC FLOW CONTRIBUTING TO
   WEAKER CONVERGENCE.  STILL...COMBINATION OF INTENSE
   PREFRONTAL/DIABATIC HEATING AND FRONTAL LIFT WILL LEAD TO AT LEAST
   WIDELY SCATTERED TSTM DEVELOPMENT WITH SPORADIC SVR GUSTS/HAIL PSBL.
    THIS THREAT WILL BE MORE LIMITED IN SPACE AND TIME THAN OVER
   CATEGORICAL OUTLOOK AREA...AND SHOULD DIMINISH AFTER DARK.
   
   ...OH TO MID-SOUTH REGION OVERNIGHT...
   LATE IN PERIOD...FROM ABOUT 8/06Z ONWARD...STRENGTHENING WIND FIELDS
   ALOFT WILL OVERSPREAD LARGER PROPORTION OF WARM SECTOR AS NRN PART
   OF MID-UPPER LEVEL SHORTWAVE PERTURBATION DEEPENS AND APCHS NEUTRAL
   TILT.  THIS CAUSES SOME CONCERN FOR SVR THREAT EXTENDING INTO
   OVERNIGHT HOURS ACROSS PORTIONS OH...CENTRAL/ERN KY AND MIDDLE
   TN...EVEN THOUGH FOREGOING AIR MASS WILL BE CHARACTERIZED BY
   SOMEWHAT WEAKER AMBIENT THETAE...AND INSTABILITY WILL DECREASE DUE
   TO DIABATIC SFC COOLING.  FCST SOUNDINGS STILL SHOW EFFECTIVE INFLOW
   PARCELS SFC-BASED OR VERY NEARLY SO EVEN AS LATE AS AROUND
   8/09Z...IN NARROW CORRIDOR AHEAD OF FRONT/CONVERGENCE LINE.  LAPSE
   RATES AND BUOYANCY EACH WILL BE WEAK...WITH MLCAPE GENERALLY AOB 300
   J/KG.  SOME CAPPING IN 750-850 MB LAYER IS EVIDENT IN PROGS...WHICH
   MAY BE OVERCOME BY FRONTAL FORCING.  GIVEN THESE UNCERTAINTIES...SVR
   PROBABILITIES AT CATEGORICAL THRESHOLDS ARE EXPANDED FARTHER E...BUT
   LOWER THAN PRIOR AFTERNOON/EVENING DUE TO CONDITIONAL NATURE OF
   INSTABILITY.
   
   ...INTERIOR MID-ATLC AND SRN NEW ENGLAND REGIONS...
   WIDELY SCATTERED TO SCATTERED TSTMS -- MOSTLY MULTICELLULAR IN MODE
   -- ARE FCST TO DEVELOP DURING AFTERNOON.  ALTHOUGH SPECIFIC FOCI FOR
   INITIATION APPEAR NEBULOUS...MOIST BOUNDARY-LAYER AIR MASS SHOULD
   EXPERIENCE STG SFC HEATING TO WEAKEN CINH.  MLCAPE SHOULD RISE INTO
   1000-2000 J/KG RANGE OVER MUCH OF THIS AREA...LOCALLY APCHG 3000
   J/KG.  ALTHOUGH LOW-MIDDLE LEVEL FLOW WILL BE MODEST THROUGH MOST OF
   DAYLIGHT HOURS...LIMITING VERTICAL SHEAR...STRENGTHENING
   UPPER/ANVIL-LEVEL FLOW WILL AID IN STORM ORGANIZATION.  ISOLATED SVR
   DOWNDRAFTS AND SPORADIC LARGE HAIL EACH ARE POSSIBLE.
   
   ..EDWARDS.. 09/07/2012
   
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