SWODY1
SPC AC 121952
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0252 PM CDT SAT SEP 12 2009
VALID 122000Z - 131200Z
...NO SVR TSTM AREAS FORECAST...
...SE TX/SRN LA TO CENTRAL GULF COAST...
EARLY AFTERNOON SURFACE ANALYSIS INDICATED AN ILL-DEFINED AREA OF
LOW PRESSURE OVER THE NWRN GULF OF MEXICO WITH A BOUNDARY EXTENDING
ENEWD TO VICINITY OF THE SERN LA COAST AND THEN EWD THROUGH THE NERN
GULF TO THE NRN FL PENINSULA. PREVIOUS FORECAST SCENARIO INDICATING
LOW PROBABILITIES FOR ISOLATED TORNADOES AND GUSTY WINDS IN STRONGER
CONVECTION REMAINS ON TRACK. NO CHANGES IN SEVERE WEATHER
PROBABILITIES HAVE BEEN MADE WITH THIS OUTLOOK ISSUANCE.
...ELSEWHERE...
MINOR CHANGES IN THE GENERAL TSTM LINE HAVE BEEN MADE OVER THE NRN
HIGH PLAINS WITH THE APPROACH OF THE CLOSED UPPER LOW...AND COASTAL
SECTIONS OF THE CENTRAL CA HAVE BEEN REMOVED FROM THE GENERAL TSTM
POTENTIAL.
..PETERS.. 09/12/2009
.PREV DISCUSSION... /ISSUED 1147 AM CDT SAT SEP 12 2009/
BLOCKED FLOW PATTERN IN PLACE ACROSS CONUS. UPPER LOW CONTINUES TO
GRADUALLY DEVELOP OVER TX AS 70KT SUB-TROPICAL JET APPROACHES FROM
NRN MEXICO PROVIDING INCREASING UPPER DIVERGENCE ACROSS SRN HALF OF
TX. ALSO IN RESPONSE TO DEVELOPMENTS ALOFT...A SURFACE LOW HAS NOW
FORMED OFFSHORE ABOUT 50 MILES E OF CRP.
WHILE CONDITIONS ARE NOT FAVORABLE FOR SIGNIFICANT DEEPENING OF THE
SURFACE LOW...SHEAR PROFILES WILL GRADUALLY INCREASE THRU THE
FORECAST PERIOD FROM THE UPPER TX COAST EWD TO SRN MS AS LOW SLOWLY
MOVES ENEWD JUST OFFSHORE TO SRN LA BY 12Z SUN.
WITH A CONTINUED FEED OF VERY MOIST/TROPICAL AIR MASS INTO LWR MS
VALLEY...CONDITIONS WILL BE FAVORABLE FOR EXTENSIVE PCPN INCLUDING
THUNDERSTORMS...PARTICULARLY THIS EVENING/OVERNIGHT WITH INCREASE OF
THE LARGE SCALE ASCENT. LOW LEVEL VEERING SHEAR PROFILES WILL
SUPPORT POTENTIAL FOR ROTATING STORMS...PROVIDED SUFFICIENT
INSTABILITY IS AVAILABLE. WITH LAPSE RATES GENERALLY LESS THAN 6C/KM
AND A SATURATED COLUMN...WILL JUST MAINTAIN A LOW THREAT FOR
ISOLATED TORNADOES AND GUSTY WINDS IN STRONGER
CONVECTION...PRIMARILY TONIGHT...MID GULF COASTAL REGION.
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