DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 011629
SWODY1
SPC AC 011627

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1027 AM CST TUE DEC 01 2009

VALID 011630Z - 021200Z

...THERE IS A SLGT RISK OF SVR TSTMS TONIGHT FOR THE LA DELTA EWD TO
THE FL PANHANDLE...

...GULF COAST AREA TONIGHT...
A STRONG SRN STREAM SHORTWAVE TROUGH OVER THE TX BIG BEND WILL BEGIN
TO ACCELERATE ENEWD LATE IN THE PERIOD IN RESPONSE TO AMPLIFICATION
OF A NRN STREAM TROUGH OVER THE CENTRAL/NRN ROCKIES AND PLAINS.
THERE ARE STILL SOME UNCERTAINTIES IN THE SPECIFIC TRACK OF THE
DEEPENING SURFACE CYCLONE WHICH WILL ACCOMPANY THE EJECTING SRN
STREAM TROUGH. RECENT SURFACE OBSERVATIONS AND SATELLITE IMAGERY
SUGGEST THAT THE MAIN BAROCLINIC ZONE IS LOCATED WELL OFF THE TX/LA
COASTS...WITH SURFACE WAVE DEVELOPMENT CLOSE TO BUOY 42002 IN THE NW
GULF AND NEAR THE SW EDGE OF THE LARGE THUNDERSTORM CLUSTER. THIS
LOCATION SUPPORTS THE MORE ERN/FASTER FORECAST EVOLUTION DEPICTED BY
THE GFS...AS WELL AS THE INITIAL SUBSYNOPTIC LOW SHOWN IN THE NAM
NEAR THE LA DELTA BY 00Z.

THE MAIN IMPLICATION OF THIS UNCERTAINTY WILL BE THE TIMING OF THE
ARRIVAL OF THE SURFACE WARM SECTOR ONSHORE FROM THE LA DELTA EWD TO
THE FL PANHANDLE. WARM SECTOR LAPSE RATES WILL BE LIMITED BY
WIDESPREAD CONVECTION AND NO UPSTREAM ELEVATED MIXED LAYER PLUME
/PER 12Z SOUNDINGS/. STILL...WEAK INSTABILITY IS EXPECTED TONIGHT
ALONG THE N CENTRAL/NE GULF COAST AS A BOUNDARY LAYER DEWPOINTS IN
THE MID-UPPER 60S SURGE INLAND WITH WARM FRONTAL PASSAGE. THE NRN
PART OF THE SURFACE WARM SECTOR WILL COINCIDE WITH VERY STRONG
LOW-MID LEVEL SHEAR...WHERE FORECAST HODOGRAPHS SHOW EFFECTIVE SRH
OF 300-500 M2/S2 AND 0-6 KM BULK SHEAR OF 50-70 KT. THE NET RESULT
WILL BE AN ENVIRONMENT SUPPORTIVE OF SUPERCELLS/BOWS EMBEDDED IN A
LARGER LINE/CLUSTER OF STORMS...WITH THE POTENTIAL FOR DAMAGING
WINDS AND A COUPLE OF TORNADOES. THERE IS ALSO SOME POTENTIAL FOR
TWO EPISODES OF CONVECTION NEAR THE COAST - THE FIRST EMANATING FROM
THE ONGOING NW GULF STORMS AND REACHING THE COAST BY EARLY
TONIGHT...AND A SECOND BAND REACHING THE COAST LATE TONIGHT. GIVEN
THE EXPECTED WEAK INSTABILITY AND CONTINUING UNCERTAINTIES WITH THE
CYCLONE TRACK/TIMING...IT IS APPROPRIATE TO MAINTAIN THE SLIGHT RISK
AREA WITH 5% TORNADO AND 15% DAMAGING WIND PROBABILITIES.

..THOMPSON/JEWELL.. 12/01/2009

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