SWODY1
SPC AC 261250
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0750 AM CDT MON SEP 26 2011
VALID 261300Z - 271200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS MORNING OVER PORTIONS OF
CNTRL/ERN KY INTO SRN OH...
...UPPER OH VALLEY...
VORTICITY MAXIMUM AND ASSOCIATED 70-75 KT MIDLEVEL JET STREAK OVER
THE LOWER OH VALLEY WILL PIVOT RAPIDLY NWD INTO LOWER MI BY
AFTERNOON. MEANWHILE...A COMPARABLE UPSTREAM VORTICITY LOBE AND JET
STREAK WILL TRANSLATE SEWD THROUGH THE LOWER OH VALLEY THIS
AFTERNOON BEFORE EJECTING NEWD ACROSS THE REGION THIS EVENING INTO
TONIGHT. IN THE LOW-LEVELS...COLD FRONT EXTENDING FROM OCCLUDED
SURFACE LOW NEAR CHICAGO SEWD THROUGH ERN IND INTO MIDDLE TN WILL
ADVANCE EWD TODAY...SERVING AS THE FOCUS FOR STRONG TO POTENTIALLY
SEVERE TSTM DEVELOPMENT. LATEST NEAR-TERM MODEL GUIDANCE SUGGESTS
THAT A WEAK SURFACE LOW WILL FORM ALONG THE FRONT OVER NERN KY LATER
TODAY WITH THIS FEATURE DEVELOPING NWD THROUGH ERN OH THIS EVENING.
A PRE-FRONTAL BAND OF TSTMS WITH EMBEDDED MESOCYCLONES HAS
INTENSIFIED THIS MORNING OVER CNTRL KY. HERE...IT APPEARS THAT
FORCING FOR ASCENT ASSOCIATED WITH LEAD IMPULSE HAS OVERSPREAD THE
NRN EXTENSION OF A NARROW AXIS OF RELATIVELY HIGHER THETA-E WHICH
HAS NOSED TO THE OH RIVER. THOUGH ENVIRONMENT REMAINS STRONGLY
SHEARED...ONGOING BAND OF STORMS ARE QUICKLY OVERSPREADING THE
NARROW INSTABILITY AXIS...SUGGESTING THAT THE MORE ORGANIZED
WIND/TORNADO THREAT MAY TEND TO DIMINISH BY LATE MORNING.
LATER TODAY...CLOUD BREAKS AND BOUNDARY LAYER DEW POINTS IN THE
LOWER 60S ARE EXPECTED TO YIELD POCKETS OF MODEST INSTABILITY WHERE
MLCAPE WILL APPROACH 1000 J/KG. LOW-LEVEL ASCENT ALONG COLD FRONT
AND PRE-EXISTING CONVECTIVE OUTFLOW BOUNDARIES IN CONCERT WITH
INCREASED FORCING ATTENDANT TO APPROACHING JET STREAK ARE EXPECTED
TO FOSTER AN INCREASE IN STORM COVERAGE AND INTENSITY FROM ERN KY
NWD INTO ERN OH. HERE...FORECAST HODOGRAPHS EXHIBIT VERTICALLY
VEERING WIND PROFILES WITH 40-50 KT OF DEEP-LAYER SHEAR...SUGGESTING
THE POTENTIAL FOR ORGANIZED/ROTATING STORMS. CURRENTLY...IT APPEARS
THAT A MORE ROBUST SEVERE WEATHER THREAT WILL BE LIMITED BY THE
MARGINAL INSTABILITY. HOWEVER...A NWD EXPANSION OF THE CATEGORICAL
SLIGHT RISK IS POSSIBLE IN SUBSEQUENT FORECASTS SHOULD IT BECOME
APPARENT THAT THE AIR MASS WILL BECOME MORE UNSTABLE THAN IS
CURRENTLY FORECAST.
...GULF COAST STATES...
COLD FRONT WILL CONTINUE TO SETTLE SEWD ACROSS THE REGION
TODAY...BECOMING PROGRESSIVELY MORE DISPLACED TO THE S OF STRONGER
MID- AND HIGH-LEVEL WIND FIELD ASSOCIATED WITH THE MIDWESTERN
SYNOPTIC SYSTEM. NONETHELESS...CONVERGENCE ALONG THE FRONT WILL
SUPPORT AN INCREASE IN STORM COVERAGE THIS AFTERNOON WITHIN A MOIST
WARM SECTOR WITH MLCAPE VALUES INCREASING TO 1500-2500 J/KG. THIS
INSTABILITY COUPLED WITH 25-35 KT OF DEEP-LAYER SHEAR MAY BE
SUPPORTIVE OF ORGANIZED MULTICELL CLUSTERS CAPABLE OF MAINLY
DAMAGING WIND GUSTS.
OVERNIGHT...INCREASING WAA ALONG AND N OF STALLING FRONT IS EXPECTED
TO CONTRIBUTE TO THE DEVELOPMENT OF ELEVATED TSTMS FROM ERN TX INTO
MS. GIVEN THE PRESENCE OF STEEP MIDLEVEL LAPSE RATES AND MODEST
CLOUD-BEARING SHEAR...A RISK FOR MARGINALLY SEVERE HAIL WILL EXIST
WITH THE STRONGEST STORMS.
..MEAD/ROGERS.. 09/26/2011
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