MESO: Mesoscale Discussion 1830

ACUS11 KWNS 290656
SWOMCD
SPC MCD 290655
ALZ000-FLZ000-MSZ000-LAZ000-290900-

MESOSCALE DISCUSSION 1830
NWS STORM PREDICTION CENTER NORMAN OK
0155 AM CDT WED AUG 29 2012

AREAS AFFECTED...PORTIONS SERN LA...SRN MS...SWRN AL...WRN PANHANDLE
OF FL.

CONCERNING...TORNADO WATCH 593...

VALID 290655Z - 290900Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 593 CONTINUES.

SUMMARY...GREATEST UNCONDITIONAL TORNADO POTENTIAL WILL CONTINUE TO
BE WITH MINI-SUPERCELLS EMBEDDED WITHIN OUTER BAND CURRENTLY
EXTENDING SEWD FROM MOB AREA ACROSS COASTAL/OFFSHORE WATERS OF AL.
INNER BANDING OFFSHORE MS COAST ALSO MAY OFFER BRIEF SPINUPS OVER
COASTAL MS AND ADJACENT ISLANDS. THESE FEATURES SHOULD EXPERIENCE
NET WWD SHIFT IN STEP WITH THAT COMPONENT OF ISAAC'S TRANSLATION.
GIVEN CONVECTIVE STRUCTURE OF THIS SYSTEM...AND DECREASE IN
LOW-LEVEL SHEAR EWD...ISOLATED SUPERCELLS E OF OUTERMOST BAND APPEAR
IMPROBABLE...AND WW MAY BE CLEARED FROM E-W ACCORDINGLY.

DISCUSSION...GREATEST JUXTAPOSITION OF BUOYANCY AND LOW-LEVEL
VERTICAL SHEAR WILL REMAIN WITH OUTER-BANDING FEATURES AND
INDIVIDUAL/EMBEDDED SUPERCELL ELEMENTS MOVING OFF GULF. IN
NOCTURNAL ABSENCE OF DIABATIC SFC HEATING...LOW-LEVEL BUOYANCY
ARISES FROM SUFFICIENT MARINE-LAYER THETAE...ADVECTING NWWD FROM
GULF ADJACENT TO OUTER BANDING AND BECOMING PART OF INFLOW LAYER FOR
EMBEDDED CELLS. MODIFIED SOUNDINGS ACCORDINGLY SUGGEST HIGHEST
OVERLAND 0-3 KM CAPE VALUES ALONG COAST FROM AL EWD...CONTRIBUTING
TO TOTAL MLCAPE OF AROUND 500-1000 J/KG. CAPE WILL CONTINUE TO
DIMINISH WITH NWWD/INLAND EXTENT DUE TO PRECIP EFFECTS...AND DROPS
OFF SHARPLY NW OF NEARLY COLLOCATED SFC TROUGH AND WEAK BAROCLINIC
BOUNDARY. AT 6Z THIS BOUNDARY WAS DRAWN FROM NEAR GPT NEWD TO NEAR
MGM...AND SHOULD MOVE SLOWLY NWWD APACE WITH TC TRANSLATION.
VWP...RAOBS AND MODIFIED MODEL SOUNDINGS SUGGEST GREATEST EFFECTIVE
SRH OVER COASTAL AL AND EXTREME SERN MS...GRADUALLY DIMINISHING WITH
EWD EXTENT AWAY FROM STRONGEST 925-850 MB WINDS THAT CONTRIBUTE TO
LARGE HODOGRAPHS. AS SMALL CAPE/SRH OVERLAP NOW OVER COASTAL AL AND
SERN MS SHIFTS WWD...SO WILL RELATIVE MAX IN TORNADO THREAT.

..EDWARDS.. 08/29/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...MOB...JAN...LIX...LCH...

LAT...LON 30288728 30198808 30238865 30188902 30008881 29698885
29538903 29398931 29358915 29258911 29218895 28948911
29058925 28818947 29098934 29218950 29278978 29079019
29019065 30239145 31429116 31878864 31138733 30428711
30288728

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