SWODY1
SPC AC 210537
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1237 AM CDT WED OCT 21 2009
VALID 211200Z - 221200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MID/UPPER-LEVEL LOW INITIALLY OVER NM WILL BEGIN TO LIFT NEWD INTO
THE CNTRL PLAINS AS STRONG VORTICITY MAXIMUM ROTATES AROUND PARENT
CIRCULATION. ASSOCIATED ZONE OF CONCENTRATED HEIGHT FALLS/DYNAMIC
FORCING FOR ASCENT WILL CONCURRENTLY SPREAD NEWD FROM THE SRN HIGH
PLAINS THROUGH KS...OK AND N TX. AT THE SURFACE...LOW PRESSURE
INITIALLY OVER WRN TX WILL DEVELOP FROM WRN TX INTO ERN OK BY THU
MORNING. TRAILING COLD FRONT WILL PUSH EWD THROUGH WRN/CNTRL PARTS
OF OK/TX.
...WRN/NRN TX INTO OK...
WARM SECTOR AIR MASS WILL CONTINUE TO MODIFY THROUGH THE
PERIOD...AIDED BY 40-50+ KT SLY LLJ...WITH DEWPOINTS INCREASING
THROUGH THE 50S INTO LOWER 60S. HOWEVER...THE COMBINATION OF
WIDESPREAD CLOUDS AND WEAK LAPSE RATES WILL LIMIT MLCAPE TO LESS
THAN 500 J/KG.
TSTMS ARE EXPECTED TO BE ONGOING AT THE ONSET OF THE FORECAST PERIOD
OVER WRN TX WITHIN ZONE OF DEEP ASCENT AHEAD OF UPPER SYSTEM. THIS
ACTIVITY WILL LIKELY INCREASE IN COVERAGE AND INTENSITY TODAY WHILE
PROGRESSING EWD IN ADVANCE OF PACIFIC FRONT. BOTH NAM AND GFS
SIMULATED WATER VAPOR IMAGERY SUGGEST THAT A MIDLEVEL DRY SLOT MAY
DEVELOP NEWD THROUGH NWRN TX INTO PARTS OF WRN/CNTRL OK THIS
AFTERNOON...POTENTIALLY SERVING TO ENHANCE STORM INTENSITY GIVEN
BREAKS IN LOW CLOUDS. STRENGTHENING...MERIDIONAL DEEP-LAYER SHEAR
ORIENTED LARGELY PARALLEL TO PACIFIC FRONT SUGGESTS THAT DOMINANT
STORM MODE MAY TREND TOWARD LINEAR.
CURRENTLY...IT APPEARS THAT THE WEAK INSTABILITY WILL LIMIT A MORE
ROBUST WIND/HAIL THREAT. THEREFORE...ONLY LOW SEVERE PROBABILITIES
WILL BE MAINTAINED.
...CNTRL/SRN TX INTO LA...
CURRENT BUOY OBS AND GOES SOUNDER PW IMAGERY INDICATE THAT BETTER
QUALITY MOISTURE /MID TO UPPER 60S DEWPOINTS/ IS NOW RETURNING NWD
THROUGH THE FAR WRN GULF OF MEXICO. THIS HIGHER THETAE AIR SHOULD
CONTINUE NWD THROUGH AT LEAST THE SERN QUARTER OF TX TODAY...ALONG
AND S OF WEAK WARM FRONT. TSTMS ARE EXPECTED TO INCREASE IN
COVERAGE AND INTENSITY THROUGH THE DAY WITHIN SRN FRINGE OF STRONGER
LOW-LEVEL WAA REGIME PRESENT ALONG SYSTEM WARM CONVEYOR BELT. HERE
TOO...WEAK LAPSE RATES WILL LIMIT THE DEGREE OF CONVECTIVE
INSTABILITY /I.E. MLCAPE LESS THAN 500-1000 J PER KG/ DESPITE THE
MOIST BOUNDARY LAYER CONDITIONS.
FORECAST HODOGRAPHS INDICATE VEERING WINDS WITH HEIGHT WITH
SUFFICIENT LOW AND DEEP-LAYER SHEAR FOR EMBEDDED ROTATING STORMS.
WHILE THE WEAK LAPSE RATES AND CONVECTIVE INSTABILITY WILL LIKELY
LIMIT A MORE SUBSTANTIAL SEVERE THREAT...SOME POTENTIAL WILL EXIST
FOR EPISODIC SUPERCELL STRUCTURES CAPABLE OF LOCALLY STRONG WINDS
AND PERHAPS A BRIEF TORNADO. EXPECT A SIMILAR THREAT TO CONTINUE
EWD/NEWD THROUGH THE SABINE RIVER VALLEY TONIGHT ALONG EWD-MIGRATING
LLJ AXIS.
..MEAD/IMY.. 10/21/2009
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