Severe Weather Watch Possible

In the latest day one convective outlook, the SPC maintains much of Alabama in their standard slight risk for severe weather today. This risk mainly includes areas along and south of Interstate 20. A very moist and unstable air mass is conducive for shower and thunderstorm development this afternoon. Storm that develop could produce damaging straight-line winds, large hail, torrential rain and frequent lightning.

As the afternoon progresses, the SPC has also included the potential for a severe weather watch for portions of Alabama. There is a 40% chance that a watch will be issued. Daytime heating is allowing the atmosphere to destabilize and with outflow boundaries in place from this morning’s activity, it will not take much to get showers and storms to develop rapidly. Storms are likely to develop across the northwestern part of the area first, and with northwest flow aloft, these storms should push off to the southeast once they develop. Storms that do develop should last through the evening hours and begin to wind down after the sun sets.

MESOSCALE DISCUSSION 1264
NWS STORM PREDICTION CENTER NORMAN OK
1057 AM CDT THU JUN 27 2013

AREAS AFFECTED…PORTIONS AL…ERN MS…GA…SC…FL PANHANDLE.

CONCERNING…SEVERE POTENTIAL…WATCH POSSIBLE

VALID 271557Z – 271830Z

PROBABILITY OF WATCH ISSUANCE…40 PERCENT

SUMMARY…INCREASING SVR THREAT IS POSSIBLE ACROSS DISCUSSION AREA
AS LOW-LEVEL AIR MASS DESTABILIZES. LARGE HAIL AND DAMAGING
GUSTS…SOMETIMES NEAR SVR LIMITS…ARE POSSIBLE.

DISCUSSION…NEARLY UNCAPPED AND INCREASINGLY BUOYANT AIR MASS FROM
SC TO ERN MS WILL SUPPORT RISK FOR DEVELOPMENT OF SFC-BASED
CONVECTION THROUGH EARLY-MID AFTN PRODUCING LARGE HAIL AND DAMAGING
DOWNBURSTS. UPSCALE GROWTH IS POSSIBLE INTO LARGER CLUSTERS
OFFERING DAMAGING-WIND RISK.

VIS IMAGERY INDICATES TWO PRIMARY INITIAL AREAS OF CONVECTIVE
CONCERN…
1. NRN GA AND NERN AL….ALONG DIFFERENTIAL HEATING ZONE THAT
COINCIDES WITH SEWD EXTENSION OF EARLIER CONVECTION…SHIFTING
SEWD…AND
2. INVOF MCV THAT ALSO IS EVIDENT IN REFLECTIVITY ANIMATIONS OVER
SERN AL…NEAR AUO. THIS FEATURE WILL PROCEED TOWARD GULF COAST OF
CENTRAL FL PANHANDLE…AND MAY AID IN CONVECTIVE ORGANIZATION FROM
THAT REGION INTO SRN AL.
OTHER CONVECTION IS LIKELY TO DEVELOP ALONG MORE SUBTLE FEATURES
WITHIN NEARLY UNCAPPED AIR MASS FROM SC TO ERN MS.

MORE KINEMATIC AND DYNAMIC SUPPORT FOR ORGANIZED SVR
POTENTIAL…COMPARED TO PREVIOUS DAYS…IS EVIDENT THROUGH AT LEAST
EARLY-MID AFTN. COOLING ALOFT…MIDLEVEL WINDS AND DEEP SHEAR EACH
WERE ENHANCED IN BMX RAOB…I.E. 35-50 KT JETLET IN 450-600 MB LAYER
AND NEARLY -12 C 500-MB TEMP — BY PROXIMAL PASSAGE OF MCV…WITHIN
SRN FRINGES OF SHORTWAVE TROUGH EXTENDING NNEWD OVER OH.
MEANWHILE…IN BROADER/MESO-ALPHA SCALE ENVIRONMENT…STRONGLY
DIFLUENT MID-UPPER LEVEL FLOW IS EVIDENT IN MORNING RAOB ANALYSES
AND MOISTURE CHANNEL IMAGERY…AHEAD OF TROUGH ALOFT. DCVA AND
ACCOMPANYING LARGE-SCALE ASCENT/DESTABILIZATION WILL ACT IN TANDEM
WITH STG INSOLATION OF MOIST BOUNDARY LAYER…CHARACTERIZED BY SFC
DEW POINTS 70S F AND TEMPS RISING INTO UPPER 80S/90S NEAR THERMAL
AXIS…YIELDING MLCAPE 2500-3500 J/KG IN MODIFIED RAOBS AND MODEL
SOUNDINGS. ENHANCEMENTS TO MIDLEVEL FLOW RELATED TO APCH OF
SHORTWAVE TROUGH ALSO WILL STRENGTHEN DEEP SHEAR. STORM MODE SHOULD
BE PRIMARILY MULTICELLULAR. HOWEVER…AT LEAST TRANSIENT
SUPERCELLULAR CHARACTER IS POSSIBLE…ESPECIALLY W AND SW OF MCV
WHERE STRONGEST FLOW ALOFT SHOULD PERSIST.

Category: Alabama's Weather, Severe Weather