SWODY1
SPC AC 120557
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1257 AM CDT MON SEP 12 2011
VALID 121200Z - 131200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER MS
VALLEY/UPPER GREAT LAKES REGION...
...SYNOPSIS...
WEAK TROUGHING ALOFT WILL LINGER OVER THE WEST...AND A SECOND TROUGH
WILL CONTINUE PROGRESSING SLOWLY EWD ACROSS THE ERN U.S. THIS
PERIOD. A STRONGER SHORT-WAVE TROUGH...HOWEVER...IS PROGGED TO
SHIFT RAPIDLY ESEWD ACROSS THE N CENTRAL U.S. TOWARD THE UPPER MS
VALLEY/UPPER GREAT LAKES -- ALONG WITH AN ASSOCIATED SURFACE FRONT.
THIS UPPER TROUGH/FRONT WILL FOCUS THE PRIMARY SEVERE POTENTIAL THIS
FORECAST PERIOD.
...UPPER MS VALLEY/GREAT LAKES REGION...
FAST-MOVING UPPER SYSTEM AND ASSOCIATED COLD FRONT ARE PROGGED TO
SUPPORT CONVECTIVE DEVELOPMENT ACROSS THE MN ARROWHEAD AND INTO NRN
WI/UPPER MI AND THE LK SUPERIOR REGION DURING THE AFTERNOON...AS
BOUNDARY LAYER HEATING BENEATH STEEPENING LAPSE RATES ALOFT YIELDS
AIRMASS DESTABILIZATION. WHILE WARM SECTOR CAPPING -- ESPECIALLY
WITH SWWD EXTENT -- SHOULD DELAY DEVELOPMENT WITHIN THE
AFOREMENTIONED AREAS AND LIKELY PRECLUDE INITIATION SW OF
MN/WI...EVENTUAL EVOLUTION OF SEVERE/ISOLATED SUPERCELL STORMS
APPEARS LIKELY ACROSS THE SLIGHT RISK AREA GIVEN INCREASINGLY
FAVORABLE KINEMATIC ENVIRONMENT. SOMEWHAT LIMITED LOW-LEVEL
MOISTURE AND LESS-THAN-FAVORABLE LOW-LEVEL SHEAR SUGGESTS THAT
SEVERE POTENTIAL SHOULD REMAIN CONFINED TO ISOLATED HAIL AND
LOCALLY-DAMAGING WINDS...WITH THREAT LIKELY TO HAVE A DIURNAL
MAXIMUM FOLLOWED BY A SLOW DECREASE THROUGH THE EVENING.
...COASTAL CAROLINAS...
COOLER AIR ALOFT ASSOCIATED WITH THE UPPER TROUGH CROSSING THE E
COAST STATES THROUGH THE DAY COMBINED WITH DAYTIME HEATING WILL
RESULT IN SOME DESTABILIZATION IN LEE OF THE ROCKIES. WITH THE
TROUGH ALSO LIKELY TO INDUCE WEAK SURFACE TROUGHING...LOW-LEVEL
ASCENT HERE -- AND INVOF SEA BREEZE BOUNDARIES -- WILL LIKELY
SUPPORT AFTERNOON STORM DEVELOPMENT. WHILE STRONGER DEEP-LAYER FLOW
AHEAD OF THE UPPER TROUGH SHOULD SLOWLY SHIFT OFFSHORE -- THUS
LIMITING OVERALL SEVERE THREAT...SOME MULTICELL ORGANIZATION WILL BE
POSSIBLE -- WITH ISOLATED/LOW-END HAIL AND/OR WIND THREAT POSSIBLE
OVER ERN PORTIONS OF THE CAROLINAS WITH STRONGER CONVECTION.
..GOSS/COHEN.. 09/12/2011
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