Sep 4, 2012 2000 UTC Day 1 Convective Outlook
Updated: Tue Sep 4 19:43:31 UTC 2012
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20120904 2000 UTC Day 1 Outlook Graphic
Probabilistic Tornado Graphic
20120904 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
20120904 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
20120904 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 041940
   
   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0240 PM CDT TUE SEP 04 2012
   
   VALID 042000Z - 051200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER GREAT LAKES TO
   MID MO VALLEY...
   
   ...THERE IS A SLGT RISK OF SVR TSTMS CENTRAL GULF COAST...
   
   ASIDE FROM LOWERING SEVERE PROBS ACROSS WRN NY/OH VALLEY NO
   APPRECIABLE CHANGES HAVE BEEN MADE TO 1630Z OUTLOOK.
   
   ...NRN PLAINS TO UPPER GREAT LAKES...
   
   CONSIDERABLE AMOUNT OF HIGH BASED CU IS DEVELOPING WITHIN STEEP
   LAPSE RATE ENVIRONMENT ACROSS THE CNTRL HIGH PLAINS EARLY THIS
   AFTERNOON.  THIS IS INDICATIVE OF MASS FIELDS BEGINNING TO ADJUST TO
   UPSTREAM SHORT-WAVE TROUGH THAT WILL FORCE A COLD FRONT ACROSS THE
   DAKOTAS LATER THIS EVENING.  LATEST THINKING IS DEEP CONVECTION
   SHOULD EMERGE WITHIN MORE MOIST ENVIRONMENT DOWNSTREAM LATER THIS
   EVENING THEN SPREAD/DEVELOP TOWARD THE UPPER MS VALLEY DURING THE
   OVERNIGHT HOURS.
   
   CU FIELD IS EXPANDING/DEEPENING FROM THE ARROWHEAD OF MN ARCING
   ACROSS WRN WI INTO SERN MN/NERN IA.  ISOLATED SEVERE THUNDERSTORMS
   SHOULD EMERGE ALONG THIS CORRIDOR OF ENHANCED LOW LEVEL CONVERGENCE
   OVER THE NEXT FEW HOURS.  EARLIER THOUGHTS REGARDING SEVERE REMAIN.
   
   ...WRN NY/OH VALLEY...
   
   MARGINAL LAPSE RATES/INSTABILITY AND DEEP LAYER SHEAR DO NOT APPEAR
   PARTICULARLY FAVORABLE FOR ORGANIZED SEVERE THUNDERSTORMS ACROSS WRN
   NY INTO PORTIONS OF THE OH VALLEY.  NUMEROUS SHOWERS/TSTMS
   DOWNSTREAM OF LAKES ONTARIO/ERIE SHOULD PROGRESS INTO PORTIONS OF
   UPSTATE NY/CNTRL PA BUT INTENSITY LEVELS SHOULD BE MOSTLY
   SUB-SEVERE.  FOR THIS REASON HAVE LOWERED SEVERE PROBS ACROSS THIS
   REGION.
   
   ..DARROW.. 09/04/2012
   
   .PREV DISCUSSION... /ISSUED 1130 AM CDT TUE SEP 04 2012/
   
   ...SYNOPSIS...
   LOW AMPLITUDE CYCLONIC FLOW WILL PREVAIL ACROSS THE NRN TIER THROUGH
   WED AS ELONGATED RIDGE PERSIST FROM THE DESERT SW TO THE LWR MS VLY.
   ELSEWHERE...ELONGATED VORT NOW OVER THE AL-GA BORDER...LARGELY THE
   REMNANT OF FORMER TC ISAAC...IS EXPECTED TO DROP S OR SSW WHILE UPR
   LOW NOW NEARING MIAMI CORRESPONDINGLY PIVOTS NNWWD JUST OFF THE E FL
   CST.
   
   LOW AMPLITUDE DISTURBANCE NOW OVER MI SHOULD CONTINUE E TO THE LWR
   GRT LKS LATER TODAY...FOSTERING DIURNALLY ENHANCED...POSSIBLY SVR
   STORMS OVER PARTS NY/PA/OH. A MORE SUBSTANTIAL UPSTREAM IMPULSE NOW
   ENTERING NW MT SHOULD AMPLIFY ESE ACROSS THE NRN PLNS LATER
   TODAY/TNGT...AND REACH MN EARLY WED. THIS FEATURE...AND A WEAKER
   DISTURBANCE AHEAD OF IT...MAY SUPPORT A COUPLE ROUNDS OF STRONG TO
   SVR STORMS OVER THE N CNTRL STATES BETWEEN NOW AND WED.
   FINALLY...AFTN HEATING EXPECTED TO REJUVENATE STORM DEVELOPMENT ON
   SWRN FRINGE OF AL/GA VORT...WITH SOME OF THE ACTIVITY POSSIBLY
   BECOMING SVR.
   
   ...NRN PLNS/UPR MS VLY THROUGH WED MORNING...
   STRONG SFC HEATING...LOW-LVL UPLIFT ALONG WEAK CONFLUENCE
   FEATURES...AND ASCENT WITH LOW AMPLITUDE DISTURBANCE CROSSING THE
   NRN PLNS MAY SUPPORT STRONG TO SVR TSTM DEVELOPMENT OVER ERN/SRN MN
   AND WRN WI LATER TODAY. THERMODYNAMIC ENVIRONMENT APPEARS FAVORABLE
   FOR BOTH VERY LARGE HAIL AND DMGG WIND. A CONDITIONAL  POTENTIAL
   ALSO WILL EXIST FOR UPSCALE DEVELOPMENT INTO A FORWARD-PROPAGATING
   MCS...WITH AN ASSOCIATED RISK FOR DMGG WIND.
   
   FARTHER W...MORE SCTD STORMS MAY FORM LATE THIS AFTN ALONG WEAK
   CONFLUENCE FEATURE IN THE ERN DAKOTAS/NRN NEB. MORE SUBSTANTIAL
   STORMS DEVELOPMENT IS EXPECTED OVER THIS REGION EWD INTO SRN MN AND
   NRN IA LATE TNGT/EARLY WED AS AMPLIFYING MT TROUGH APPROACHES
   REGION. STRENGTH OF FLOW /WITH 700 MB SPEEDS AOA 50 KTS/ AND
   AVAILABILITY OF RICH MOISTURE ON NWRN FRINGE OF DEVELOPING LLJ
   SUGGEST POTENTIAL EVOLUTION INTO A SIZABLE MCS...POSSIBLY ONE
   CONTAINING EMBEDDED SUPERCELLS AND BOWING STRUCTURES WITH HIGH
   WIND/HAIL THAT COULD PERSIST ACROSS REGION BEYOND 12Z WED.
   
   ...LWR GRT LKS THIS AFTN...
   ASCENT WITH MI UPR IMPULSE AND ASSOCIATED LOW LVL MOISTURE INFLOW
   FROM THE OH VLY/MID ATLANTIC WILL INCREASE TSTM COVERAGE/STRENGTH
   OVER PARTS OF OH...PA...AND NY LATER TODAY...ALONG AND AHEAD OF WEAK
   COLD FRONT NOW EXTENDING FROM ERN ONT TO NW OH. CLOUDS WILL LIMIT
   LOW LVL DESTABILIZATION...ESPECIALLY IN OH...AND LOW-LVL SHEAR WILL
   REMAIN WEAK. BUT SUFFICIENT DEEP SHEAR WILL BE PRESENT FOR
   SUSTAINED/ORGANIZED STORMS...SOME OF WHICH COULD POSE A THREAT FOR
   LOCALLY DMGG WIND AND PERHAPS MARGINALLY SVR HAIL TIL EARLY EVE.
   
   ...CNTRL GULF CST THIS AFTN/EVE...
   SFC HEATING ON WRN AND SWRN FRINGE OF REMNANT UPR VORT FROM ISAAC
   EXPECTED TO SUPPORT RENEWED STORM DEVELOPMENT FROM CNTRL/ERN MS SSE
   TO THE CNTRL GULF CST LATER TODAY...DESPITE THE FACT THAT REGION
   LARGELY WILL BE EXPERIENCING NEUTRAL OVER EVEN NEGATIVE DCVA. RICH
   LOW-LVL MOISTURE AND MODERATELY VEERING DEEP WIND PROFILES SHOULD
   ONCE AGAIN FOSTER SUSTAINED STORMS AND POSSIBLY AN EMBEDDED
   SUPERCELL OR TWO POSING A RISK FOR DMGG WIND AND PERHAPS A TORNADO.
   THE SVR THREAT SHOULD DIMINISH LATER TNGT.
   
   ...S FL THIS AFTN...
   COOL MID LVL TEMPS AND WEAK UPR DIVERGENCE ON WRN FRINGE OF OFFSHORE
   LOW MAY YIELD AN ENHANCED RISK FOR A FEW PULSE STORMS WITH LOCALLY
   DMGG WIND AND SVR HAIL THROUGH LATE AFTN IN S FL.
   
   ...CNTRL/SRN PLNS...
   ISOLD SVR STORMS WILL BE POSSIBLE LATE THIS AFTN/EVE INVOF WEAK W-E
   BOUNDARY IN SRN/WRN KS AND THE OK/TX PANHANDLE REGION...WHERE STEEP
   LOW TO MID LVL LAPSE RATES WILL EXIST BENEATH MODEST DEEP
   FLOW/FORCING FOR ASCENT.
   
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   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z