SPC AC 311257

   DAY 1 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0757 AM CDT FRI JUL 31 2015

   VALID 311300Z - 011200Z

   ...THERE IS A MRGL RISK OF SVR TSTMS PORTIONS NEB TO NRN MO...

   ...THERE IS A MRGL RISK OF SVR TSTMS PORTIONS SERN CONUS...

   ...SUMMARY...
   ISOLATED MARGINALLY SEVERE STORMS WILL BE POSSIBLE ACROSS PARTS OF
   THE CENTRAL PLAINS THIS AFTERNOON AND EVENING...AS WELL AS PARTS OF
   THE SOUTHEASTERN U.S.

   ...SYNOPSIS...
   IN MID-UPPER LEVELS...PATTERN WILL BE DOMINATED BY MEAN TROUGHING
   OVER ERN NORTH AMERICA...ANCHORED BY QUASISTATIONARY/ SYNOPTIC-SCALE
   CYCLONE OVER HUDSON BAY...AND RIDGING ASSOCIATED WITH ANTICYCLONE
   CENTERED OVER SRN ROCKIES/4-CORNERS REGION.  TWO SOMEWHAT CONJOINED
   BELTS OF RELATIVELY MAXIMIZED 250-MB CYCLONIC FLOW WILL
   PERSIST...ONE FROM MB ACROSS UPPER GREAT LAKES AND ST. LAWRENCE
   VALLEY...ANOTHER FROM NRN PLAINS TO OH VALLEY TO SRN NEW ENGLAND. 
   MOST PROMINENT SHORTWAVES WILL BE EMBEDDED WITHIN NRN FLOW
   BELT...WITH ONLY VERY PERIPHERAL INFLUENCE AT MOST OVER OUTLOOK
   AREAS BELOW IN TERMS OF SLIGHTLY ENHANCED HEIGHT GRADIENT ALOFT. 
   HOWEVER...DIFLUENT FLOW WILL BE COMMON FROM CENTRAL PLAINS TO SERN
   CONUS...ALONG AND S OF SRN FLOW BELT...GIVEN GEOMETRY OF HEIGHT
   FIELDS ASSOCIATED WITH WRN CONUS HIGH AND WEAK/PERSISTENT/POSITIVELY
   TILTED TROUGHING OVER FL PENINSULA. 

   AT SFC...LEADING COLD FRONT WAS DRAWN ON 11Z CHART FROM NEW
   BRUNSWICK SSWWD ACROSS ATLC TO ERN NC AND CENTRAL SC...THROUGH WEAK
   FRONTAL-WAVE LOW OVER CENTRAL GA...AND ANOTHER NEAR PNS...THEN
   ARCHING WWD ACROSS SRN LA AND E-CENTRAL/N-CENTRAL TX.  FRONT WAS
   PRECEDED BY OUTFLOW BOUNDARIES ALONG MUCH OF ITS LENGTH FROM
   TX-CAROLINAS.  THIS FRONT SHOULD BECOME QUASISTATIONARY THROUGH
   PERIOD WITH GRADUAL WEAKENING.  FARTHER N...DIFFUSE COLD FRONT WAS
   ANALYZED FROM SWRN QUE ACROSS LE...SRN LM...TO WEAK LOW OVER CENTRAL
   SD.  THIS BOUNDARY SHOULD BECOME QUASISTATIONARY ALSO.  SEPARATE
   FRONTAL SEGMENT WAS EVIDENT FROM NERN MO WNWWD ACROSS WRN NEB...WITH
   VERY SLGT NWD MOVEMENT POSSIBLE THROUGH PERIOD.  

   ...CENTRAL PLAINS TO NORTHWEST MO/SOUTHWEST IA...
   ISOLATED TO WIDELY SCATTERED TSTMS -- BOTH DISCRETE AND IN CLUSTERS
   -- ARE EXPECTED TO DEVELOP ACROSS THIS CORRIDOR INVOF FRONTAL
   SEGMENT.  RETURN OF MODIFIED...SLIGHTLY MOISTENED CONTINENTAL
   TRAJECTORIES FROM PRIOR FROPA...COMBINED WITH
   EVAPOTRANSPIRATION...SHOULD CONTRIBUTE SUFFICIENT MOISTURE TO
   SUPPORT UP TO 2500 J/KG MLCAPE IN TANDEM WITH STG SFC HEATING THIS
   AFTN.  WELL-MIXED SUBCLOUD LAYER BENEATH INCREASINGLY WEAK MLCINH
   WILL SUPPORT POTENTIAL FOR MAINTENANCE OF STG-SVR GUSTS AND HAIL TO
   SFC WITH MOST INTENSE/SUSTAINED CONVECTION.  MOSTLY MULTICELLULAR
   MODES ARE EXPECTED...BUT WITH STG VERTICAL VEERING IN WIND PROFILE
   BENEATH SRN RIM OF AFOREMENTIONED UPPER-LEVEL CYCLONIC
   FLOW...TRANSIENT SUPERCELLULAR CHARACTER ALSO MAY APPEAR.  THOUGH
   ENVIRONMENT FAVORS LOCALIZED CONCENTRATIONS OF SVR THREAT...GREATER
   UNCONDITIONAL SVR PROBABILITIES ARE PRECLUDED ATTM BY LACK OF THESE
   FACTORS -- STRONGER LOW-LEVEL FLOW...BETTER-DEFINED
   CONVERGENCE...AND GREATER LOW-LEVEL SHEAR. 

   ...SERN CONUS...
   SCATTERED-NUMEROUS TSTMS IN CLUSTERS...WITH MANY CELL/CLUSTER
   MERGERS...ARE FCST TODAY WITHIN AND S OF FRONTAL ZONE.  STG SFC
   HEATING...LIFT NEAR FRONTAL-SEA-BREEZE/OUTFLOW BOUNDARIES...VERY
   RICH LOW-LEVEL MOISTURE...AND WEAK CAPPING PER MODIFIED 12Z CHS/JAX
   RAOBS AND MODEL SOUNDINGS...ALL ARE EXPECTED.  THAT HEATING ALONG
   WITH PW APCHG 2 INCHES WILL OFFSET MODEST LAPSE RATES ALOFT ENOUGH
   TO YIELD PRECONVECTIVE MLCAPE 1000-2000 J/KG.  MOST INTENSE CORES
   WILL OFFER POTENTIAL FOR DAMAGING WET DOWNBURSTS.  BETTER-ORGANIZED
   SVR THREAT SHOULD BE PRECLUDED BY LACK OF DEEP-LAYER FLOW/SHEAR.

   ...OH VALLEY/GREAT LAKES...
   ISOLATED TSTMS MAY DEVELOP THIS AFTN INVOF FRONTAL ZONE...AS MLCINH
   MINIMIZED BY DIABATIC HEATING AND WEAK FRONTAL LIFT CONTRIBUTE TO
   CORRIDOR OF CONVECTIVE POTENTIAL.  HOWEVER...VERY WEAK
   MID/UPPER-LEVEL LAPSE RATES NOTED IN MORNING ILN/ILX RAOBS CARRY
   THROUGH THIS AFTN IN MOST MODEL FCST SOUNDINGS...GREATLY LIMITING OR
   EVEN ELIMINATING DEEP CAPE IN SOME AREAS.  DUE TO RELATED
   COVERAGE/INTENSITY QUESTIONS...PREVIOUS MRGL OUTLOOK ACCORDINGLY HAS
   BECOME TOO CONDITIONAL TO MAINTAIN.

   ..EDWARDS/JIRAK.. 07/31/2015

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