Sep 6, 2012 1730 UTC Day 2 Convective Outlook
Updated: Thu Sep 6 17:32:45 UTC 2012
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20120906 1730 UTC Day 2 Outlook Graphic
Probabilistic Graphic
20120906 1730 UTC Day Probabilitic Graphic
Probability of severe weather within 25 miles of a point.
Hatched Area: 10% or greater probability of significant severe within 25 miles of a point.
   SPC AC 061730
   
   DAY 2 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   1230 PM CDT THU SEP 06 2012
   
   VALID 071200Z - 081200Z
   
   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE OZARKS REGION THROUGH
   THE MID MS/LOWER OH VALLEYS INTO SRN LOWER MI...
   
   ...SYNOPSIS...
   MODELS CONTINUE TO INDICATE AMPLIFICATION OF THE LONGWAVE PATTERN
   ACROSS THE LOWER 48 STATES DURING THE DAY 2 PERIOD...AS A
   POSITIVELY-TILTED SHORTWAVE TROUGH DIGS SEWD FROM THE NRN PLAINS/
   UPPER MS VALLEY INTO THE GREAT LAKES AND LOWER OH/MID MS VALLEYS TO
   THE OZARKS REGION BY 12Z SAT. MEANWHILE...A PORTION OF A SHORTWAVE
   TROUGH...CURRENTLY MOVING INTO NRN NV PER WATER VAPOR
   IMAGERY...SHOULD TRACK SEWD IN TANDEM WITH THE PRIMARY AMPLIFYING
   UPPER TROUGH AND REACH THE MID MS/LOWER OH VALLEYS LATER FRI
   AFTERNOON/EARLY EVENING.
   
   AT THE SURFACE...HIGH PRESSURE WILL BUILD ACROSS THE CENTRAL TO SRN
   PLAINS FORCING A COLD FRONTAL SURGE SEWD AND SWD TO A POSITION FROM
   SERN LOWER MI THROUGH FAR WRN KY...CENTRAL AR TO NRN AND SOUTHWEST
   TX BY 08/00Z.  BY 12Z SAT...THE COLD FRONT IS EXPECTED TO EXTEND
   FROM QUEBEC THROUGH THE LOWER GREAT LAKES/UPPER OH VALLEY TO THE
   LOWER MS VALLEY AND SOUTH CENTRAL TX.
   
   ...SRN LOWER MI LOWER OH/MID MS VALLEYS TO OZARKS REGION...
   GIVEN THE STRONG DYNAMICS AND MASS RESPONSE EXPECTED WITH THE
   AMPLIFYING SHORTWAVE TROUGH DURING DAY 2 WITH 60-90 METER 500 MB
   HEIGHT FALLS FORECAST ACROSS THESE AREAS...AN EXPANSIVE SLIGHT RISK
   AREA IS BEING MAINTAINED WITH A LITTLE NWWD AND NWD EXPANSION OF
   THIS RISK. THE 12Z NAM/GFS ARE TRENDING A LITTLE SLOWER WITH THE
   TIMING OF THE COLD FRONT PASSAGE ACROSS THE SRN GREAT LAKES...
   SHOWING A WARM FRONT POTENTIALLY REACHING SRN LOWER MI FRI AFTERNOON
   WITH THE SURFACE LOW TRACKING INTO OR AT LEAST ALONG THE SRN LOWER
   MI BORDER REGION BETWEEN 18-00Z.  GIVEN THESE TRENDS IN THE MODELS
   WITH GREATER DESTABILIZATION DEVELOPING/SPREADING FARTHER NWD...THE
   SLIGHT RISK AREA HAS BEEN EXPANDED TO INCLUDE THE REST OF NRN IND
   AND NWRN OH INTO SRN LOWER MI.  THE SLIGHT RISK HAS ALSO BEEN
   EXPANDED A LITTLE NWWD TO INCLUDE MORE OF NERN MO AND CENTRAL IL.
   
   SHOWERS AND TSTMS ARE EXPECTED TO BE ONGOING AT 12Z FRI FROM PARTS
   OF THE CENTRAL PLAINS INTO THE UPPER MS VALLEY/MIDWEST REGION. 
   SURFACE HEATING ALONG THE ERN PERIPHERY OF THIS ACTIVITY WILL AID IN
   DESTABILIZING THE DOWNSTREAM AIR MASS WHERE PW VALUES OF 1-2 INCHES
   WILL BOOST FRIDAY AFTERNOON MUCAPE TO 1500-2500 J/KG.  THIS COMBINED
   WITH FRONTOGENETIC FORCING ALONG A STRENGTHENING/SHARPENING COLD
   FRONT AND DIFFLUENT FLOW ALOFT WILL SUPPORT INCREASING UPWARD
   VERTICAL MOTION FOR TSTM DEVELOPMENT FROM LATE MORNING THROUGH THE
   AFTERNOON AND EVENING AS THE COLD FRONT SURGES SEWD AND SWD. 
   EFFECTIVE BULK SHEAR WILL BE STRONG AND SUFFICIENT FOR ORGANIZED
   STORMS WITH BOTH LEWPS AND SUPERCELLS POSSIBLE.  DAMAGING WINDS AND
   HAIL WILL BE LIKELY.  A TORNADO THREAT WILL BE POSSIBLE...ESPECIALLY
   ACROSS THE NRN EXTENT OF THE SLIGHT FROM NERN IL/NRN IND/NWRN OH
   INTO SRN LOWER MI WHERE LOW LEVEL SHEAR/HODOGRAPH CURVATURE WILL BE
   GREATER INVOF THE SURFACE LOW TRACK AND WARM FRONT.
   
   TSTMS WILL CONTINUE AFTER DARK ALONG THE PROGRESSIVE COLD FRONT...
   BUT A DIURNAL DECREASE IN INSTABILITY SUGGESTS THE SEVERE THREAT
   SHOULD GRADUALLY DIMINISH.
   
   ...PARTS OF THE LOWER GREAT LAKES REGION...
   SCATTERED SHOWERS AND THUNDERSTORMS SHOULD EVOLVE THROUGH THE DAY
   ACROSS THE MID ATLANTIC REGION INTO NY...AS AFTERNOON AIR MASS
   DESTABILIZATION OCCURS GIVEN SURFACE HEATING BENEATH THE ERN EXTENT
   OF THE EML/STEEPER MIDLEVEL LAPSE RATE PLUME. MUCAPE VALUES SHOULD
   RANGE FROM 1000-1500 J/KG WITH THE HIGHER VALUES IN THE MID ATLANTIC
   REGION. STRONGER BULK SHEAR SHOULD NOT BE JUXTAPOSED WITH THE
   GREATER INSTABILITY...AS SHEAR IS EXPECTED TO BE WEAKER WITH SRN
   EXTENT FROM THE LOWER GREAT LAKES/NY.  THIS SUGGESTS AN ISOLATED
   WIND/HAIL THREAT REMAINS AN ADEQUATE SEVERE RISK DURING THE FIRST
   HALF OF THE PERIOD.
   
   MEANWHILE...STORMS ARE EXPECTED TO BECOME MORE NUMEROUS FRI NIGHT
   ACROSS THE LOWER GREAT LAKES TO THE UPPER OH VALLEY AS THE COLD
   FRONT APPROACHES FROM THE WEST. FLOW ALOFT WILL INCREASE THROUGH THE
   EVENING AND FRIDAY NIGHT.  HOWEVER...THIS WILL OCCUR DURING THE
   DIURNALLY LESS FAVORABLE THERMODYNAMIC ENVIRONMENT.  THUS...THE
   SEVERE RISK SHOULD REMAIN LIMITED AFTER DARK...WITH THE PRIMARY
   THREAT IN THE FORM OF ISOLATED GUSTY WINDS...GIVEN THE EXPECTED
   STRENGTHENING OF A SWLY LLJ.
   
   ..PETERS.. 09/06/2012
   
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