SWODY2
SPC AC 211714
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1214 PM CDT WED OCT 21 2009
VALID 221200Z - 231200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
IN MID-UPPER LEVELS...PROGRESSIVE SHORTWAVE PATTERN FCST TO CONTINUE
OVER CONUS..DOMINATED BY SERIES OF PERTURBATIONS CONTRIBUTING TO
TROUGHING OVER CENTRAL CONUS. MID-UPPER LOW -- NOW ANALYZED OVER
NERN NM -- IS FCST TO EJECT NEWD FROM CENTRAL PLAINS TO ERN IA THIS
PERIOD...SHRINKING AND WEAKENING INTO OPEN-WAVE PERTURBATION.
BROADLY CYCLONIC FLOW WILL BE MAINTAINED ACROSS CENTRAL/S-CENTRAL
CONUS IN WAKE OF THIS FEATURE. MEANWHILE...NRN STREAM SHORTWAVE
TROUGH -- NOW INLAND PACIFIC NW -- IS FCST TO MOVE EWD ACROSS NRN
ROCKIES...NRN HIGH PLAINS AND CANADIAN PRAIRIE PROVINCES DAY-2.
LOW-MIDLEVEL VORTICITY MAX LEFT OVER FROM PACIFIC TC RICK IS
EXPECTED TO EJECT NEWD ACROSS MEX DAY-1...THEN FROM TX COAST TO SRN
APPALACHIANS DAY-2 WHILE WEAKENING.
AT SFC...FRONTAL-WAVE CYCLONE IS FCST TO MOVE FROM VICINITY KS/MO
BORDER TO WRN/CENTRAL IL THROUGH PERIOD. MEANWHILE...TRAILING COLD
FRONT WILL MOVE EWD/SEWD TO WRN TN...WRN MS...SERN LA AND WELL
OFFSHORE TX COAST BY 23/12Z.
...WRN/CENTRAL GULF COAST AND LOWER DELTA REGIONS...
SCATTERED/EPISODIC TSTMS ARE EXPECTED THROUGHOUT PERIOD -- BOTH
ALONG COLD FRONT AND IN PREFRONTAL REGIME OF STG LOW LEVEL WAA AND
MOISTURE TRANSPORT. A FEW GUSTS NEAR SVR LEVELS AND CONDITIONAL
TORNADO THREAT EACH ARE POSSIBLE...BUT ORGANIZED SVR RISK APPEARS
TOO LOW ATTM FOR CATEGORICAL OUTLOOK.
DEEP-LAYER LAPSE RATES WILL REMAIN WEAK -- SLIGHTLY ABOVE MOIST
ADIABATIC ON AVERAGE -- LIMITING BUOYANCY IN MOST AREAS. GIVEN SUCH
UNFAVORABLE THERMODYNAMIC ENVIRONMENT...POTENTIAL FOR LARGE HAIL
WILL BE MINIMAL...EVEN WITH ANY SUPERCELLS THAT MAY DEVELOP...AND
PREDOMINANT FRONTAL MODE WILL BE LINEAR. DEEP-LAYER WIND FIELDS AND
SHEAR GENERALLY WILL INCREASE WITH NWD EXTENT FROM W-CENTRAL GULF
COAST REGION...WHILE PROBABILITY OF FAVORABLE INSTABILITY BECOMES
SMALLER. SVR PROBABILITIES -- ALREADY MRGL -- THEREFORE BECOME MORE
CONDITIONAL FROM NRN LA ACROSS AR AND WRN/CENTRAL MS.
DESTABILIZATION AND GENERATION OF APPRECIABLE CAPE IS MOST PROBABLE
WITHIN ABOUT 100 NM OF COAST...WHERE MOST COMPLETELY MODIFIED AND
HIGHEST THETAE BOUNDARY LAYER AIR MASS WILL BE PRESENT...PERHAPS
COLLOCATED WITH ENOUGH BREAKS IN CLOUDS FOR POCKETS OF SUSTAINED SFC
DIABATIC HEATING. ACCORDINGLY MODIFIED ETA-KF SOUNDINGS YIELD
OPTIMAL MLCAPE IN 500-1000 J/KG RANGE...WITH LESS THAN 500 J/KG
EXPECTED IN MOST AREAS. COLD FRONT IS EXPECTED TO OUTPACE INLAND
RETREAT OF MARINE AIR AT SFC ACROSS MS/AL...SHRINKING FAVORABLE
WARM-SECTOR AIR MASS COASTWARD WITH EWD EXTENT THROUGH PERIOD. LOW
LEVEL HODOGRAPHS NEAR NERN EDGE OF RICHEST GULF RETURN-FLOW AIR DO
SUGGEST SOME POTENTIAL FOR RELATIVELY DISCRETE CELLS TO
ROTATE...WITH FCST 0-1 KM SRH 100-200 J/KG.
..EDWARDS.. 10/21/2009
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