Thursday, December 24, 2009

New Discussion From SPC

MESOSCALE DISCUSSION 2285
NWS STORM PREDICTION CENTER NORMAN OK
0114 PM CST THU DEC 24 2009

AREAS AFFECTED...CENTRAL/SRN MS...FAR SERN LA AND FAR SWRN AL

CONCERNING...TORNADO WATCH 808...

VALID 241914Z - 242015Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 808 CONTINUES.

EARLY AFTERNOON SURFACE ANALYSIS INDICATED A DEEPENING AREA OF LOW
PRESSURE OVER SERN OK WITH A COLD FRONT EXTENDING SSEWD THROUGH SWRN
AR AND INTO WRN LA. A WARM FRONT EXTENDED SEWD FROM THE LOW INTO
NERN LA...SWRN MS TO SERN MS AND OFFSHORE OF THE WRN FL PANHANDLE.

SQUALL LINE EXTENDING FROM SERN LA NWWD THROUGH NEW ORLEANS INTO
SWRN MS IS MOVING EWD AT 25-30 KT AND WILL CONTINUE TO OVERTAKE THE
WARM SECTOR ACROSS FAR SERN LA INTO SOUTH CENTRAL/SERN MS THIS
AFTERNOON. THE SPEED OF THE SQUALL LINE IS FASTER THAN THE WARM
SECTOR HAS BEEN ABLE TO ADVANCE INLAND THUS FAR ACROSS SERN MS.
SOME BOUNDARY LAYER MODIFICATION /MOISTENING AND WARMING/ INTO SERN
MS/FAR SWRN AL IS EXPECTED YET THIS AFTERNOON...GIVEN SOME RECENT
DECREASE IN CLOUDS PER VISIBLE IMAGERY. THIS SUGGESTS THE SRN THIRD
TO ONE HALF OF WW 808 SHOULD BE THE PRIMARY TORNADO THREAT AREA
THROUGH MID-LATE AFTERNOON.

DESPITE WEAK INSTABILITY...EFFECTIVE BULK SHEAR /40-50 KT/ AND
EFFECTIVE SRH /200-400 M2/S2/ SUGGEST A TORNADO OR TWO REMAINS
POSSIBLE WITHIN THE WARM SECTOR. ADDITIONAL THREAT FOR
STRONG/DAMAGING WINDS IS EXPECTED ACROSS ALL OF WW 808...ESPECIALLY
WITH ANY BOWING STRUCTURES...AS DOWNDRAFTS TRANSPORT HIGH MOMENTUM
AIR /60-70 KT SLY LLJ WHICH EXTENDED FROM SERN LA INTO MS/ TO THE
SURFACE.

..PETERS.. 12/24/2009


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