MESO: Mesoscale Discussion 1542

ACUS11 KWNS 272129
SWOMCD
SPC MCD 272129
ALZ000-MSZ000-LAZ000-280000-

MESOSCALE DISCUSSION 1542
NWS STORM PREDICTION CENTER NORMAN OK
0429 PM CDT SAT JUL 27 2013

AREAS AFFECTED...PORTIONS OF SRN LA...SRN MS...SWRN AL

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 272129Z - 280000Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...AN ISOLATED SVR THREAT MAY EXIST INTO THE EVENING HOURS.
WHILE TRENDS WILL BE MONITORED...THE ISSUANCE OF A WW IS CURRENTLY
UNLIKELY.

DISCUSSION...MODEST MID-LEVEL ASCENT IN THE BASE OF A BROAD
ERN-CONUS TROUGH IS ENCOURAGING THUNDERSTORM DEVELOPMENT ALONG/AHEAD
OF A COLD FRONT THAT EXTENDS FROM SFC LOW PRESSURE CENTERED OVER
S-CNTRL MS SWWD INTO SWRN LA. A WEAK STATIONARY FRONT CONNECTS THE
SFC LOW TO NEAR MOBILE BAY. THE AIR MASS BOUNDED BY THESE TWO FRONTS
IS MODERATELY UNSTABLE OWING TO DIURNAL HEATING OF RICH
BOUNDARY-LAYER MOISTURE -- E.G. SFC DEWPOINTS IN THE LOWER/MIDDLE
70S. MARGINAL INSTABILITY EXISTS E OF THE WEAK STATIONARY FRONT
WHERE A SLIGHTLY COOLER AIR MASS IS PRESENT IN ASSOCIATION WITH MORE
LIMITED INSOLATION.

LIX VWP DATA INDICATE AROUND 25 KT OF 3-KM-AGL FLOW ATOP SUBTLE
VERTICAL VEERING OF THE WIND PROFILE...YIELDING MODEST LOOPING OF
LOW-LEVEL HODOGRAPHS. AND...WITH SUFFICIENTLY STRONG HIGHER-LEVEL
FLOW SUPPORTING AROUND 30 KT OF DEEP SHEAR...ORGANIZED CONVECTIVE
CLUSTERS COULD TRACK ACROSS THE REGION THROUGH THE EVENING HOURS. A
FEW INSTANCES OF DMGG WIND GUSTS CANNOT BE RULED OUT...AIDED BY
WATER-LOADING PROCESSES WITH HIGH PW -- I.E. OVER 2 INCHES IN MANY
AREAS PER GPS DATA. GIVEN BACKGROUND STREAMWISE VORTICITY IN THIS
MOIST ENVIRONMENT...THE POTENTIAL FOR A TORNADO CANNOT BE COMPLETELY
RULED OUT. HOWEVER...RELATIVELY WEAK LOW-LEVEL CONVERGENCE IS
EVIDENT IN VWP/SFC DATA...WHICH MAY CONTRIBUTE TO LIMITED COVERAGE
OF A MORE ORGANIZED SVR THREAT. HOWEVER...TRENDS WILL BE MONITORED
THROUGH THE EVENING HOURS.

..COHEN/CORFIDI.. 07/27/2013

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

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

LAT...LON 30109357 30599220 31458903 31028778 30128761 29288886
29109068 29499332 30109357

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