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000
FXUS64 KBMX 220028
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
728 PM CDT TUE MAY 21 2013

.DISCUSSION...

EARLY EVENING SURFACE MESO-ANALYSIS SHOWS A PAIR OF (OR THREE)
BIG OUTFLOW BOUNDARIES ACROSS THE SOUTHERN PORTION OF THE
COUNTRY...WITH ACTIVE CONVECTION ALONG THEIR LEADING EDGES. THE
FIRST BOUNDARY WAS IN EASTERN TN...ABOUT TO MOVE ACROSS THE
MOUNTAINS. THE TRAILING SOUTHERN EDGE OF THAT BOUNDARY MAY BE
LINGERING NEAR THE TN/AL STATE LINE. THE OTHER OUTFLOW BOUNDARY
STRETCHED FROM SOUTHERN IL SOUTHWARD...INTERSECTING THE FIRST
BOUNDARY JUST EAST OF MEMPHIS...AND THEN ARCING BACK TO THE
SOUTHWEST NORTHERN LA AND EASTERN TX. THAT LATTER BOUNDARY IS
ACTUALLY A MERGER OF TWO THAT EARLIER WERE A BIT MORE DISCRETE.
EACH BOUNDARY HAD A PRETTY WELL DEFINED MESO-HIGH BEHIND IT
HELPING TO PUSH IT ALONG.

THE BIG QUESTION OF COURSE IS WHETHER THE THUNDERSTORMS ASSOCIATED
WITH THE SECOND BOUNDARY WILL BE ABLE TO CONTINUE. AND IF
SO...THEN HOW FAR AND HOW STRONG? SPC MESOSCALE PARAMETERS STILL
SHOW A GOOD BIT OF INSTABILITY IMMEDIATELY DOWNSTREAM OF THE
ONGOING LINE OF STORMS...IN THE FORM OF 1500-2000 J/KG OF SURFACE
BASED CAPE. LOW LEVEL SHEAR...HOWEVER...REALLY IS LACKING (WITH
0-6 KM BULK SHEAR WELL BELOW 30 KTS...AND 0-1 KM SHEAR LESS THAN
10 KTS). THUS...EVEN IF THE STORMS WERE ABLE TO CONTINUE ON AND
REACH THE WESTERN PORTION OF OUR CWA...THEY SHOULD BE/REMAIN BELOW
SEVERE LEVELS BY THE TIME THEY GET HERE. IF THEY ARE ABLE TO HOLD
TOGETHER...A RULE OF THUMB ANALYSIS PUTS THE LINE OF STORMS AT
MARION COUNTY BETWEEN 10 AND 11 PM.

ASSUMING CONDITIONS DON`T CHANGE DRASTICALLY...FOR THE EVENING
FORECAST UPDATE THE MAIN ADJUSTMENT WILL BE TO BUMP UP THE TIMING
(BY ABOUT 3 HOURS) ON THE CHANCES OF STORMS INTO THE WEST. I THINK
HIGH CHANCE POPS (40-50 PERCENT) ARE STILL JUSTIFIED FOR
NOW...ALTHOUGH I MAY EXPAND THE AREA OF CHANCE POPS EASTWARD JUST
A BIT (PERHAPS AS FAR EAST AS JASPER AND TUSCALOOSA). OTHER
FORECAST ELEMENTS (INCLUDING DEW POINTS) LOOK FINE AT THIS POINT.

/61/

&&

.AVIATION...
00Z TAF DISCUSSION.

AT THIS TIME...CURRENT THINKING...AND WITH MODEL CONSENSUS IS
THAT THE LINE WILL DETERIORATE AS IT MOVES SE TOWARD C AL INTO
LESS FAVORABLE AREA OF SOMEWHAT WEAKEN BUT STILL HIGH PRESSURE.
ALSO...WITH SUNSET STORMS SHOULD LOSE SOME OF THEIR PUNCH. SO WITH
THAT SAID...WILL LEAVE OUT FOR TONIGHT FOR C AL TAFS AS
PROBABILITY IS LOW THAT THIS LINE WILL MAKE IT...BUT WILL CONTINUE
TO CLOSELY MONITOR THROUGH THE EARLY EVENING FOR SIGNS THAT STORMS
COULD HOLD TOGETHER. FOR NOW...NOT EXPECTING CONVECTION TILL WED
AFTERNOON JUST AHEAD OF THE FRONT WITH ONLY VCTS/VCSH FOR NOW...
WITH BEST CHANCES NRN TAFS. ALTHOUGH AN ISOLATED MVFR CIG/VIS IS
NOT OUT OF THE QUESTION...THINK THAT MOST OF THE NIGHT WILL BE
VFR WITH MID AND HIGH CLOUDS MOVING IN THROUGH THE NIGHT.

08


&&

.BMX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$