Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 311259
SWODY1
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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