MESO: Mesoscale Discussion 1831

ACUS11 KWNS 291047
SWOMCD
SPC MCD 291046
ALZ000-FLZ000-MSZ000-LAZ000-291215-

MESOSCALE DISCUSSION 1831
NWS STORM PREDICTION CENTER NORMAN OK
0546 AM CDT WED AUG 29 2012

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

CONCERNING...TORNADO WATCH 593...

VALID 291046Z - 291215Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 593 CONTINUES.

SUMMARY...TORNADO THREAT CONTINUES IN MIDDLE-OUTER BANDS OF THIS
SYSTEM...AND SHOULD SHIFT INLAND/NWWD WITH TIME THROUGH REMAINDER
MORNING. THREAT ALSO MAY INCREASE INLAND DURING DAY. AS
SUCH...NEW/REPLACEMENT WW IS LIKELY...95%...BEFORE SCHEDULED 12Z
EXPIRATION OF WW 593.

DISCUSSION...AS CENTER OF ISAAC PROCEEDS GENERALLY NWWD...PER NHC
FCSTS...SPIRAL BANDS WITH EPISODIC/EMBEDDED SUPERCELLS WILL SHIFT
TORNADO THREAT INLAND/NWWD IN STEP WITH PARENT CIRCULATION. A FEW
SHORT-LIVED/WEAK MESOCYCLONES HAVE BEEN EVIDENT OVERNIGHT NE OF
CENTER...IN ENVIRONMENT CHARACTERIZED BY LARGE HODOGRAPHS AND
EFFECTIVE SRH 300-600 J/KG OVER EXTREME SERN MS AND SRN AL. THIS
SRH REMAINS BEST JUXTAPOSED WITH FAVORABLE CAPE OVER EXTREME SERN MS
AND SWRN AL. MODIFIED RAOBS AND FCST SOUNDINGS SUGGEST MLCAPE
RANGES FROM AROUND 100-200 J/KG OVER LOWER PEARL RIVER REGION TO
AROUND 500 J/KG BETWEEN MOB-PNS. FAVORABLE BUOYANCY SHOULD SPREAD
INLAND THROUGH DAYLIGHT HOURS...WITH COMBINATION OF SUBTLE DIABATIC
HEATING AND INLAND TRANSPORT/ADVECTION OF HIGH-THETAE MARINE AIR ON
EITHER SIDE OF SPIRAL BANDS. SUCH DESTABILIZATION SHOULD OCCUR IN
GRADUAL/PATCHWORK FASHION DUE TO OFFSETTING/STABILIZING EFFECTS OF
PERSISTENT PRECIP AREAS. ALSO...UNLIKE IN PREVIOUS STAGES OF THIS
SYSTEM...CONVECTIVE ASYMMETRY IS INCLINED TOWARD MOST FAVORABLE
CAPE/SHEAR SECTOR N THROUGH ESE OF CENTER.

NET EFFECT SHOULD BE INCREASE IN FAVORABLE CAPE/SHEAR OVERLAP DURING
DAY...AND THEREFORE...MAINTAINED AND PERHAPS INCREASED TORNADO
POTENTIAL WITH TIME. ISOLATED/WEAKER CELLS ALONG FRINGE OF
CIRCULATION...S OF WRN FL PANHANDLE...WILL POSE NONZERO BUT
SUBSTANTIALLY LOWER TORNADO RISK THAN BANDED CONVECTION..SINCE IT
WILL REMAIN IN ENVIRONMENT OF HIGHER CAPE BUT MORE MRGL SHEAR.

..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 31378784 30698730
30288728

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