SWODY1
SPC AC 011945
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0145 PM CST TUE DEC 01 2009
VALID 012000Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS TONIGHT FOR THE LA DELTA EWD TO
THE FL PANHANDLE...
...GULF COAST AREA TONIGHT...
FEW CHANGES TO ONGOING FORECAST SCENARIO...WITH SLIGHT RISK CALIBER
TORNADO/DAMAGING WIND PROBABILITIES MAINTAINED FOR TONIGHT FOR GULF
COASTAL PORTIONS OF LA/MS/AL AND FL PANHANDLE. ONGOING CONVECTIVE
CLUSTER OVER THE CENTRAL GULF OF MEXICO SHOULD CONTINUE TO REINFORCE
A BAROCLINIC ZONE THAT ROUGHLY BISECTS THE GULF PER OCEANIC
OBSERVATIONS/VISIBLE SATELLITE...WITH CONTINUED CYCLOGENESIS NOTED
IN THE WAKE OF THESE STORMS OVER THE WESTERN GULF /PER BUOYS 42020
AND 42002/. THIS SCENARIO SUGGESTS THE APPROACH OF A WARM/MOIST
MARINE AIRMASS AND CORRESPONDING SURFACE BASED SEVERE POTENTIAL WILL
BE TEMPORALLY/SPATIALLY CONFINED TO SOUTHERN LA THIS EVENING...AND
OTHERWISE THE LATTER SEVERAL HOURS OF THE PERIOD EARLY WEDNESDAY
ALONG THE MS/AL/FL PANHANDLE COAST. GIVEN LATTER PERIOD SURFACE
BASED DESTABILIZATION INLAND ATTENDANT TO AN ENCROACHING MARINE
AIRMASS...INCREASINGLY STRONG DEEP LAYER SHEAR/LOW LEVEL SRH WOULD
SUPPORT A RISK FOR DAMAGING WINDS/TORNADOES.
..GUYER.. 12/01/2009
.PREV DISCUSSION... /ISSUED 1027 AM CST TUE DEC 01 2009/
...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.
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