000
FXUS64 KBMX 131546
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
1046 AM CDT THU JUN 13 2013

.UPDATE...
MESOSCALE UPDATE.

&&

.DISCUSSION...

ACTIVE AFTERNOON AND EVENING STILL IN THE CARDS HERE ACROSS CENTRAL
ALABAMA AS A FRONTAL BOUNDARY PUSHES SOUTHWARD ACROSS THE REGION
BRINGING POSSIBLE SEVERE STORMS TO THE AREA.

LOOKING AT THE CURRENT BIG PICTURE...SFC LOW PRESSURE CENTER IS NOW
NEAR PENNSYLVANIA WITH THE TRAILING COLD FRONT STRETCHING
SOUTHEASTWARD THRU THE MISSOURI BOOTHILL AND INTO EXTREME NORTHERN
ARKANSAS. SATELLITE ALSO INDICATES A NARROW CLOUD LINE ACROSS
NORTHERN AL/MS IN ASSOCIATION WITH WHAT APPEARS TO BE A WEAKNESS
IN THE MID LEVELS. BETWEEN THESE TWO FEATURES (FRONT/CLOUD LINE)
ARE SEVERAL OUTFLOW BOUNDARIES FROM PREVIOUS/ONGOING CONVECTION
AND AREAS OF WEAK CONVERGENCE SEEN ACROSS KY/TN. AS OF THIS
WRITING...RADAR INDICATES LITTLE TO NO CONVECTION JUST TO THE
NORTH OF ALABAMA...OTHER THAN A COUPLE SMALL RETURNS NEAR THE
TN/KY LINE.

CLOSER TO HOME...SFC RIDGING CONTINUES TO WEAKEN AS THE
TROUGH/FRONT APPROACH FROM THE NORTH. TEMPS ARE ALREADY IN THE
MID/UPPER 80S WITH HIGHS EXPECTED TO BE IN THE LOW/MID 90S. DEW
POINTS ARE STILL IN THE LOW 70S ACROSS THE BOARD. AFTER SOME
MESOSCALE ANALYSIS OVER OUR AREA...NO BOUNDARIES COULD BE DETECTED
ACROSS THE CWA. WITH NO LIFTING MECHANISM CURRENTLY IN THE
VICINITY STILL DO NOT EXPECT CONVECTIVE INITIATION UNTIL THE
FRONTAL BOUNDARY MOVES NEARER/INTO THE AREA.

AS FAR AS THE SETUP FOR THIS AFTERNOON/EVENING IS CONCERNED...NOT
MUCH HAS CHANGED. WITH RATHER LITTLE NEW GUIDANCE TO CONSIDER AT
THIS JUNCTURE HAVE NOT MADE ANY MAJOR CHANGES TO POP/WX GRIDS FOR
THE SYSTEM. TIMING STILL LOOKS GOOD FOR NOW...GENERALLY 3 PM NORTH
TO 10 PM SOUTH...GIVE OR TAKE AN HR. QUESTIONS REMAIN WITH REGARDS
TO THE OVERALL COVERAGE OF STORMS AHEAD OF THE FRONT. WILL STORMS
BE MORE SCATTERED AND IN CLUSTERS...OR WILL THEY EVENTUALLY CONGEAL
INTO A SOLID LINEAR FEATURE? IT LOOKS LIKE ONLY TIME WILL
TELL...UNFORTUNATELY.

SEVERE WEATHER PARAMETERS REMAIN ABOUT THE SAME. SOUNDING PROFILES
STILL INDICATE PLENTY OF INSTABILITY...DRY AIR ALOFT...AND STEEP
LOW LEVEL LAPSE RATES. DOWNDRAFT CAPES ARE ALSO RATHER HIGH.
THEREFORE DAMAGING WINDS WILL REMAIN THE HIGHEST THREAT...FOLLOWED
BY LARGE HAIL AND FREQUENT CLOUD-TO-GROUND LIGHTNING.
HOWEVER...THERE ARE A COUPLE OF OTHER THINGS TO CONSIDER THAT
COULD HINDER ORGANIZED DEVELOPMENT. FIRST...MEAN MOISTURE REMAINS ON THE
LOW SIDE...WITH ALL MOISTURE RESIDING IN THE LOWEST LEVELS.
SECOND...CONVERGENCE JUST AHEAD OF THE FRONT DOESN`T LOOK VERY
STRONG THANKS TO WESTERLY SFC WINDS AND NW WINDS ALOFT. WE ARE PLANNING
ON DOING A SPECIAL BALLOON RELEASE AROUND 20Z THIS AFTERNOON TO
BETTER SAMPLE THE ATMOSPHERE JUST PRIOR TO THE ARRIVAL OF THE
SYSTEM. LOOK FOR ADDITIONAL UPDATES AS WE MOVE INTO THE AFTERNOON
HOURS.

ONE MORE THING TO TALK ABOUT FOR TODAY...HEAT. THE ONGOING HOT AND
HUMID CONDITIONS COULD RESULT IN HEAT INDEX VALUES AROUND 105
DEGREES FOR UP TO A COUPLE HOURS IN THE WEST. THEREFORE A HEAT
ADVISORY REMAIND IN EFFECT UNTIL 6 PM FOR COUNTIES GENERALLY ALONG
AND WEST OF INTERSTATE 65.

19

&&

.AVIATION...
12Z TAF DISCUSSION.

VERY BRIEF MVFR VIS IN BR WILL BE AT EET/TCL/TOI...WITH CONDITIONS
QUICKLY IMPROVING BY 13Z. HOT AND HUMID CONDITIONS WILL PREVAIL
TODAY. THE OVERALL ATMOSPHERIC MOISTURE CONTENT IS LIMITED BUT WE
SHOULD EXPERIENCE SOME SCATTERED CUMULUS DEVELOPMENT LATE THIS
MORNING. A COLD FRONT APPROACHES CENTRAL ALABAMA THIS AFTERNOON
WITH A NICE LOW LEVEL MOISTURE POOL JUST AHEAD OF IT. WILL THE
FORCING AND MOISTURE BE ENOUGH TO PRODUCE THUNDERSTORMS...SOME
POTENTIALLY SEVERE. HAVE HIGHER CONFIDENCE AT THIS TIME THAT A FEW
CLUSTERS DEVELOP ACROSS THE EASTERN HALF OF THE AREA.
THEREFORE...KEPT PREVAILING THUNDER IN FOR BHM/EET/ANB WHILE
TCL/MGM/TOI WILL ONLY HAVE VCTS MENTIONED AT THIS TIME. CLASSIC
INVERTED V SOUNDINGS WOULD INDICATE THE POTENTIAL FOR DAMAGING
STRAIGHT LINE WINDS ASSOCIATED WITH THE STRONGER OR ORGANIZED
ACTIVITY. TIMED THE NORTHERN SITES AROUND 22-23Z AND THE SOUTHERN
SITES AROUND 01-02Z.

THE PRESSURE GRADIENT TIGHTENS TODAY AND WILL KEEP THE MENTION OF
WESTERLY WINDS GUSTING TO 20-25KTS AHEAD OF THE FRONT...SWINGING
AROUND TO THE NORTHWEST AND LIGHTER POST FRONTAL.

75

&&

.PREV DISCUSSION... /ISSUED 649 AM CDT THU JUN 13 2013/

DISCUSSION...

THE HIGHLY ANTICIPATED AND ADVERTISED COLD FRONT THAT IS EXPECTED TO
PRODUCE SEVERE STORMS THIS AFTERNOON AND EVENING ACROSS CENTRAL
ALABAMA IS CURRENTLY MAKING ITS WAY SOUTH AND EASTWARD FROM THE
GREAT PLAINS. THE FRONT IS TRAILING FROM AN AREA OF SURFACE LOW
PRESSURE THAT WILL QUICKLY MOVE EASTWARD ACROSS NORTHERN INDIANA AND
CENTRAL OHIO THIS MORNING. FIRST...BEFORE THE FRONT GETS HERE WE`LL
HAVE SOME HEAT TO DEAL WITH. SHORT-RANGE GUIDANCE IS IN GOOD
AGREEMENT WITH LOW-LEVEL POOLING OF MOISTURE AHEAD OF THE FRONT IN THE
FORM OF LOW TO MID 70S DEWPOINTS...ESPECIALLY ALONG AND WEST OF
THE INTERSTATE 65 CORRIDOR. WITH HIGHS EXPECTED TO BE IN THE 94 TO
96 DEGREE RANGE...HEAT INDEX VALUES HAVE A GOOD CHANCE OF RISING
ABOVE 105 DEGREES FOR 2-3 HOURS THIS AFTERNOON. THEREFORE...WE ARE
GOING TO GO AHEAD AND ISSUE A HEAT ADVISORY FOR COUNTIES GENERALLY ALONG
AND WEST OF THE INTERSTATE 65 CORRIDOR.

NOW FOR THE PRIMARY THREAT...SEVERE STORMS THIS AFTERNOON AND
EVENING. IT SEEMS LIKE THIS TIME OF THE YEAR WE ALWAYS SEE SOME TYPE
OF NORTHWESTERLY FLOW ALOFT MISCHIEF IN MAY OR JUNE...AT LEAST THAT
SEEMS TO HAVE BEEN THE CASE OVER THE LAST 4 OR 5 YEARS OR SO. TODAY
WILL BE NO EXCEPTION...AND THE NORTHWESTERLY FLOW WILL ONCE AGAIN
PLAY A PART IN THE FORMATION OF SEVERE STORMS THIS AFTERNOON AND
EVENING. THE HOT CONDITIONS THAT I TALKED ABOUT EARLIER...AS WELL AS
PLENTY OF MOISTURE TO WORK WITH AT THE SURFACE...WILL NO DOUBT BE IN
PLACE AHEAD OF THE FRONT. SHORT RANGE GUIDANCE CONTINUES TO AGREE
ON MU CAPE VALUES OF AT LEAST 3000 J/KG FOR MUCH OF CENTRAL
ALABAMA LATE THIS AFTERNOON AND INTO THE EARLY EVENING HOURS. AS
THE NORTHWEST FLOW ALOFT REALLY BEGINS TO KICK IN THIS
AFTERNOON...THUNDERSTORMS THAT DEVELOP WILL BE ABLE BETTER SUSTAIN
THEIR UPDRAFTS WITH 0-6KM BULK SHEAR VALUES OF 30-35 KTS. WITH THE
AMOUNT OF INSTABILITY THAT WILL BE IN PLACE...EXPLOSIVE UPDRAFTS
DUE TO VERY STEEP LAPSE RATES WILL EASILY BE ABLE TO REACH THE
HAIL GROWTH ZONE BETWEEN -10 AND -30C EVEN THOUGH THE 500MB
TEMPERATURE WILL BE QUITE WARM AT -6 TO -7C. WITH DRY AIR ALOFT
AND INVERTED V SOUNDING PROFILES...ANY SEVERE STORM THAT DEVELOPS
COULD HAVE A BETTER CHANCE OF PRODUCING LARGE HAIL THAT REACHES
ALL THE WAY TO THE SURFACE BEFORE MELTING TOO MUCH. THIS WILL BE
THE CASE WITH THE INITIAL STORMS THAT DEVELOP LATE THIS AFTERNOON
AS THE FRONT APPROACHES OUR NORTHERN COUNTIES. AFTER THE INITIAL
DEVELOPMENT HOWEVER...WE WILL HAVE TO CLOSELY WATCH FOR A
TRANSITION TO CLUSTERS OR LINES OF STORMS THAT WILL PRODUCE THE
GREATEST THREAT OF DESTRUCTIVE WIND GUSTS. THE INVERTED V SOUNDING
PROFILES ARE VERY FAVORABLE FOR DAMAGING WIND GUSTS POSSIBLY UP TO
80 MPH TO MIX DOWN TO THE SURFACE WITH THE AMPLE AMOUNTS OF DRY
AIR ALOFT.

SO NO DOUBT ABOUT IT...WE WILL BE PRIMED FOR SEVERE STORM
DEVELOPMENT THIS AFTERNOON AND EVENING. THERE ARE A FEW LIMITING
FACTORS IN PLACE THAT COULD AT LEAST HINDER MORE IN THE WAY OF
WIDESPREAD SEVERE STORMS. THE AMOUNT OF MEAN MOISTURE THROUGHOUT THE
ENTIRE PROFILE IS LACKING...AND WE ARE ONLY BOTTOM LOADED AT THE
SURFACE WITH MOISTURE. ALSO...THE BEST MOISTURE CONVERGENCE ALONG
AND OUT AHEAD OF THE COLD FRONT BASED ON THE LATEST SHORT-RANGE
GUIDANCE WILL BE ACROSS EASTERN ALABAMA THROUGH GEORGIA AND THE
CAROLINAS. THESE LIMITING FACTORS COULD PREVENT MORE IN THE WAY OF
WIDESPREAD SEVERE DEVELOPMENT ACROSS OUR WESTERN COUNTIES...AND
WE`VE GONE AHEAD AND INCLUDED LIKELY POPS GENERALLY ALONG AND EAST
OF INTERSTATE 65 LATE THIS AFTERNOON AND EVENING. HIGH CHANCE POPS
WERE INCLUDED GENERALLY WEST OF INTERSTATE 65. I`M CERTAINLY NOT
TRYING TO DOWNPLAY THE RISK OF SEVERE STORMS THIS AFTERNOON...AS
ALL OF CENTRAL ALABAMA WILL STILL HAVE THE RISK OF SEVERE STORMS.
HIGH RESOLUTION MODELS SUCH AS THE NSSL 4KM WRF AND HRRR ARE
HINTING AT MORE ORGANIZED SEVERE CONVECTION DEVELOPING CLOSER TO
THE BETTER MOISTURE CONVERGENCE REGION ACROSS EASTERN ALABAMA AND
WESTERN GEORGIA AS WELL...MOVING SOUTH SOUTHEASTERLY THROUGH THE
EVENING HOURS.

ALL THIS BEING SAID...THE MESOSCALE WILL STILL PLAY A HUGE ROLE ON
THE OVERALL COVERAGE OF SEVERE CONVECTION TODAY. IF STORMS ARE ABLE
TO FIRE OFF TO OUR NORTHWEST AND PRODUCE AN ORGANIZED COLD
POOL...SLAB-LIKE LIFTING WILL BE LIKELY ALONG THE COLD POOL AND LEAD
TO MORE WIDESPREAD SEVERE CONVECTION AND A WIDESPREAD DAMAGING WIND
THREAT DOWNSTREAM. WATCHING THE MESOSCALE WILL BE EXTREMELY IMPORTANT TODAY
LIKE IT IS DURING ANY SEVERE EVENT...AND I ENCOURAGE EVERYONE TO
KEEP A CLOSE WATCH FOR FORECAST UPDATES THROUGHOUT THE DAY. EVEN
THOUGH WE ARE IN A SLIGHT RISK TODAY...THE POTENTIAL IS THERE OF A
MORE WIDESPREAD SEVERE WIND EVENT THIS AFTERNOON AND EVENING.
FOLKS NEED TO MAKE SURE THAT IF THEY ARE PLACED UNDER A SEVERE
THUNDERSTORM WARNING TO TAKE IT VERY SERIOUSLY TODAY.

TIMING FOR THE COLD FRONT IS STILL ON TRACK WITH THE PREVIOUS
THINKING...WITH THE FRONT MAKING IT INTO OUR NORTHERN COUNTIES BY
4-6PM...THE INTERSTATE 20 CORRIDOR BY 8-10PM...AND REACHING OUR
SOUTHERN COUNTIES AFTER MIDNIGHT TONIGHT. IF THE SHOWERS AND STORMS
ARE ABLE TO FORM A GOOD COLD POOL THAT RACES SOUTHWARD WE COULD SEE
THE SEVERE THREAT ENDING SOONER BEFORE THE FRONT ACTUALLY PASSES
THROUGH. FOLLOWING THE PASSAGE OF THE FRONT RELATIVELY DRIER AND
COOLER AIR WILL MOVE IN FOR THE DAY ON FRIDAY AND DRY CONDITIONS ARE
EXPECTED THROUGH THE WEEKEND WITH MODIFYING TEMPERATURES. THE NEXT
CHANCE OF RAIN SHOULD COME IN BY NEXT MONDAY AS A FRONTAL BOUNDARY
TRIES TO PUSH INTO THE SOUTHEAST ASSOCIATED WITH A WEAK TROUGH
FORMING OVER THE GREAT LAKES REGION.

56/GDG

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     93  67  86  62  90 /  60  20   0   0   0
ANNISTON    93  68  88  63  90 /  60  30   0   0   0
BIRMINGHAM  94  68  88  66  91 /  60  20   0   0   0
TUSCALOOSA  96  70  90  66  93 /  50  30   0   0   0
CALERA      94  70  89  66  91 /  60  30   0   0   0
AUBURN      94  72  87  68  90 /  30  60   0   0   0
MONTGOMERY  97  74  92  67  94 /  20  60   0   0   0
TROY        97  74  91  68  92 /  10  60   0   0   0

&&

.BMX WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY UNTIL 6 PM CDT THIS EVENING FOR THE FOLLOWING
COUNTIES: BIBB...FAYETTE...GREENE...HALE...JEFFERSON...LAMAR...
MARENGO...MARION...PERRY...PICKENS...SHELBY...SUMTER...
TUSCALOOSA...WALKER...WINSTON.

&&

$$