Latest Mesoscale Discussion Continues Heightened Severe Weather Risk in Louisiana, Mississippi & Alabama


Continuing to monitor the latest on the severe weather in the deep south today. I will be posting blog entries off & on. I am tracking a storm near Lexington, Mississipii with strong rotation. And at the time of this post, a tornado was on the ground 20 miles southwest of Crandall, Mississippi. This is only the start of the severe outbreak. Read below what the Storm Prediction Center has to say about this and the expansion of severe weather watches eastward as well.

MESOSCALE DISCUSSION 0436
NWS STORM PREDICTION CENTER NORMAN OK
1028 AM CDT FRI APR 15 2011

AREAS AFFECTED…PORTIONS MS…NERN LA…CENTRAL/SRN AL.

CONCERNING…TORNADO WATCH 140…

VALID 151528Z – 151730Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 140 CONTINUES.

CONTINUE WW ALONG AND S OF QUASI-LINEAR CONVECTIVE SYSTEM DELINEATED
BELOW. PER COORD W/MOB…PERRY/GEORGE/GREENE COUNTIES MS ARE BEING
ADDED TO WW AND MOBILE/WASHINGTON/CLARKE COUNTIES AL. ADDITIONAL WW
MAY BE REQUIRED DURING NEXT FEW HOURS ACROSS PORTIONS CENTRAL/SRN AL
AS WELL.

15Z SFC MESOANALYSIS AND CLOUD LINES IN VIS IMAGERY EACH INDICATE
COLD FRONT FROM MO OZARKS SSEWD TO NEAR MLU…THEN SWWD TO NEAR HOU.
COLD FRONT WILL CONTINUE TO MOVE EWD ACROSS LA AND INTO NWRN
MS…PRECEDED BY CONFLUENCE ZONE ANALYZED INITIALLY NEAR
TVR…HEZ…BTR…PTN LINE. CONFLUENCE LINE ALSO IS EXPECTED TO
SHIFT EWD ACROSS SERN LA AND SRN MS. RELATIVELY VEERED SFC FLOW
BETWEEN CONFLUENCE LINE AND COLD FRONT SHOULD MAKE WIND PROFILES
MORE UNIDIRECTIONAL WITH HEIGHT AND FOSTER MORE LINEAR MODE FOR
CONVECTION FORMING ALONG COLD FRONT. MEANWHILE…SLY/SSELY WINDS
BETWEEN CONFLUENCE LINE AND WARM FRONT WILL CONTRIBUTE MORE ENLARGED
HODOGRAPHS AND 300-500 J/KG EFFECTIVE SRH…FAVORING MORE DISCRETE
SUPERCELL/TORNADO POTENTIAL IN THAT SECTOR. THIS INCLUDES CELLS
OVER SERN MS/SWRN AL…AS WELL AS PRE COLD-FRONTAL CONVECTION NEAR
MS RIVER MOVING E OF CONFLUENCE LINE. THIS SECTOR WILL BE
CHARACTERIZED ALSO BY MLCAPE INCREASING TO NEAR 2000 J/KG THROUGH
18Z. VIS IMAGERY ALSO INDICATES DIFFERENTIAL HEATING BOUNDARY
SHOULD BECOME MORE PRONOUNCED ALONG SRN FRINGE OF CLOUD PLUME
EMANATING FROM MCS…I.E. FROM TALLADEGA AREA WSWWD TO NEAR MEI.
THIS COULD PROVIDE FOCUS FOR EVENTUAL INSTABILITY GRADIENT AND
VORTICITY ENHANCEMENT FOR ANY SUPERCELLS TRACKING NEAR IT.

PRIMARY QLCS…AS OF 15Z…WAS LOCATED FROM SHARKEY COUNTY MS OVER
CBM…WHERE IT INTERSECTED SFC WARM FRONT…THEN NEWD OVER
PROGRESSIVELY MORE STABLE BOUNDARY LAYER OVER NWRN AL AND MARSHALL
COUNTY TN. THAT SEGMENT OF QLCS SW OF WARM FRONT WILL CONTINUE TO
POSE RISK OF DAMAGING GUSTS AND A FEW TORNADOES…ESPECIALLY WITH
EMBEDDED MESOCIRCULATIONS/SUPERCELLS. MS SEGMENT MIGHT RETREAT
SLIGHTLY NWD. SVR POTENTIAL IS FCST TO DIMINISH WITH NEWD EXTENT
FROM WARM FRONT AS FOREGOING LAYER OF NEAR-SFC STATIC STABILITY
DEEPENS…LESSENING POTENTIAL FOR SVR GUSTS TO PENETRATE TO SFC.
HOWEVER…WARM FRONT WILL LIFT NEWD ACROSS SRN/CENTRAL
AL…COMBINING WITH SFC DIABATIC HEATING S OF DIFFERENTIAL-HEATING
ZONE TO DESTABILIZE AIR MASS SIGNIFICANTLY THROUGH EARLY AFTERNOON.
THEREFORE ADDITIONAL WW MAY BE NEEDED E OF WW 140.

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