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000
FXUS64 KBMX 171528
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
1028 AM CDT FRI MAY 17 2013

.UPDATE...
MORNING UPDATE.

&&

.DISCUSSION...

MCS STILL SLOWLY TRYING TO WORK INTO THE NORTHWESTERN PORTION OF
CENTRAL ALABAMA. TAKING A LOOK AT CLOUD TOPS...THEY HAVE REMAINED
FAIRLY COOL AS THE MASS WORKS IN ALTHOUGH THERE HAS BEEN SOME
WARMING ALOFT AS INDICATED WITH IR THIS MORNING. THIS IS EXPECTED
AS THE CLOUD COVER HAS BEEN EXTENSIVE OVER THE NORTHWEST AND THE
MCS IS GETTING FURTHER AWAY FROM THE FRONT. THE MAIN COOLING OF
THE CLOUDS CONTINUES TO BE ON THE BACKSIDE OF THE MCS IN
NORTHWESTERN MISSISSIPPI.

GIVEN THIS TREND WILL CONTINUE TO KEEP THE SEVERE WORDING IN THE
HWO AS ANY STORMS THAT GET GOING IN MS COULD SLIDE INTO THE
NORTHWEST...BUT GIVEN THE COOLER AIRMASS...SHOULD SEE THE
WEAKENING TREND TO CONTINUE IN CENTRAL ALABAMA...BUT A STRONG
STORM WILL DEFINITELY BE POSSIBLE. UPDATES ARE OUT.



16

&&

.AVIATION...
12Z TAF DISCUSSION.

AN UPPER LEVEL DISTURBANCE WILL APPROACH CENTRAL ALABAMA THIS
MORNING RESULTING IN SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS
ACROSS MUCH OF THE AREA BY THIS AFTERNOON. THERE IS UNCERTAINTY AS
TO WHETHER ACTIVITY WILL BECOME ORGANIZED OR REMAIN SCATTERED. FOR
NOW WILL USE VCTS WORDING UNTIL TRENDS CAN BE ESTABLISHED. CIGS WILL
REMAIN VFR THROUGH THIS EVENING. AS CONVECTION DIMINISHES THIS
EVENING...CIGS WILL LOWER TO MVFR WITH SCATTERED SHOWERS REMAINING
POSSIBLE OVERNIGHT ACROSS THE NORTH.

WITH CONTINUE MOIST LOW LEVEL INFLOW NORTHWARD...EXPECT SLIGHTLY
LOWER CIGS AT MGM AND TOI OVERNIGHT. GUIDANCE IS LEANING TOWARD
CONDITIONS LOWER THAN MVFR. EXTENSIVE CLOUD COVER COULD PREVENT
THESE LOWER CIGS/VIS...AND WILL MAINTAIN MVFR CONDITIONS FOR NOW.

14


&&

.PREV DISCUSSION...
/ISSUED 340 AM CDT FRI MAY 17 2013/

CURRENT WATER VAPOR IMAGERY DEPICTS AN UPPER TROUGH OVER THE
MID-MISSISSIPPI RIVER VALLEY WITH ANOTHER WEAK TROUGH ACROSS THE
CENTRAL PLAINS. THE TROUGH OVER THE MID-MISSISSIPPI RIVER VALLEY IS
CURRENTLY TRANSITIONING INTO MORE OF AN OPEN WAVE AS IT IS FORECAST
TO WEAKEN OVER THE COMING DAYS. AT THE SURFACE...HIGH PRESSURE HAS
SHIFTED TO THE EAST OVER THE ATLANTIC. THERE REALLY IS NO WELL
DEFINED LOW PRESSURE TO SPEAK OF UNDER THE UPPER TROUGH. A FEW
RETURNS ARE SHOWING UP ON RADAR AND A SLIGHT CHANCE OF SHOWERS WILL
CONTINUE ACROSS MUCH OF THE FORECAST AREA THROUGH THE MORNING HOURS.
THE ATMOSPHERE IS STILL RELATIVELY DRY OVER THE FORECAST AREA BUT IS
IN THE PROCESSES OF SATURATING AS MID-LEVEL WINDS BECOME MORE
SOUTHERLY AHEAD OF THE APPROACHING TROUGH.

THE UPPER LEVEL TROUGH WILL REMAIN JUST TO THE NORTHWEST OF THE
FORECAST AREA TODAY. SHOWERS AND POSSIBLY A THUNDERSTORM WILL MOVE
IN ACROSS NORTHWEST ALABAMA THIS MORNING. RELATIVELY DRIER AIR AND A
BIT OF A CAPPING INVERSION FROM WARM AIR ALOFT COULD KEEP THINGS
MOSTLY DRY THROUGH THE MORNING HOURS. MODEL SOUNDINGS INDICATE THAT
CONVECTIVE TEMPERATURES WILL BE IN THE UPPER 70S TO LOW 80S TODAY
ACROSS NORTHWEST ALABAMA WITH A BIT MORE CAPPING TO THE SOUTH AND
EAST. EXPECT SHOWERS AND THUNDERSTORMS WILL DEVELOP THIS AFTERNOON
WITH BEST COVERAGE ACROSS THE NORTHWEST. MODELS VARY A GOOD BIT WITH
THE AMOUNT OF INSTABILITY THE NAM IS ONLY SHOWING ABOUT 1000-1500
J/KG OF SBCAPE ACROSS WEST ALABAMA...WHILE THE GFS IS MORE
AGGRESSIVE WITH UPWARDS OF 2000 J/KG OF SBCAPE ACROSS WEST ALABAMA.
THE DIFFERENCE APPEARS TO BE DUE TO SMALL VARIABILITY IN SURFACE
DEWPOINTS. CURRENTLY LEANING MORE TOWARDS THE GFS WITH RATHER
IMPRESSIVE SURFACE DEWPOINTS ALREADY IN PLACE AND EXPECT THIS
ADVECTION OF HIGH THETA E AIR WILL CONTINUE ACROSS THE AREA. 500
MB FLOW IS RATHER WEAK BUT THERE WILL BE SOME DIFFLUENT FLOW
ACROSS NORTHWESTERN ALABAMA LATER THIS AFTERNOON AND EVENING. 0-6
KM BULK SHEAR IS A BIT MORE IMPRESSIVE WITH THE LATEST MODELS
INDICATING AROUND 35 KTS THIS AFTERNOON AND EVENING. DUE TO THE
VARIABLES MENTIONED ABOVE...SPC HAS INCLUDED AREAS NORTH AND WEST
OF A LIVINGSTON TO TUSCALOOSA TO JASPER LINE IN A SLIGHT RISK.
BASED ON THE SEVERE WEATHER PARAMETERS IT DOES NOT APPEAR TO BE
UNREASONABLE TO THINK THAT A COUPLE OF STORMS COULD BE BECOME
SEVERE LATER THIS AFTERNOON AND EVENING WITH DAMAGING WINDS AND
LARGE HAIL BEING THE MAIN THREATS. ADDITIONALLY...INCREASED POPS
FOR THIS AFTERNOON TO LIKELY ACROSS WESTERN PORTIONS OF ALABAMA
WITH A RATHER SHARP CUT OFF IN PRECIPITATION FURTHER TO THE
SOUTHEAST. MODELS INDICATE RATHER DECENT MOISTURE CONVERGENCE OVER
THE NORTHERN THIRD OF THE FORECAST AREA TONIGHT. PW VALUES WILL
INCREASE TO NEAR 1.75 INCHES AS THE UPPER LEVEL SHORTWAVE TROUGH
MOVES OVERHEAD. HAVE INCREASED POPS TO LIKELY CATEGORY FOR AREAS
NORTH OF THE I-20 CORRIDOR. EXPECT STORM INTENSITY WILL DECREASE
INTO THE OVERNIGHT HOURS WITH BEST CHANCES FOR SEVERE WEATHER
BETWEEN 3 TO 8 PM.

AN UPPER LEVEL RIDGE WILL AMPLIFY OVER THE WEEKEND AND THE UPPER
LEVEL TROUGH WILL LIFT OFF TO THE NORTHEAST. HOWEVER...THE ATMOSPHERE
WILL REMAIN RATHER SATURATED ACROSS THE FORECAST AREA THANKS TO
CONTINUED SOUTHERLY LOW LEVEL FLOW. INSTABILITY WILL REMAIN RATHER
IMPRESSIVE MOVING INTO THE DAY SATURDAY WITH THE BEST FORCING OVER
NORTHEASTERN PORTIONS OF CENTRAL ALABAMA. THE DEEP LAYER SHEAR
SHOULD BE WEAKER BUT STILL WOULD NOT BE SURPRISED TO SEE A FEW
STRONG STORMS WITH GUSTY WINDS AND SMALL HAIL. THERE COULD BE THE
POSSIBILITY FOR AN ISOLATED SEVERE STORM...BUT CONFIDENCE IS NOT VERY
HIGH WITH THE WAVE WEAKENING AND LIFTING OFF TO THE NORTHEAST.
SHOWERS AND THUNDERSTORMS WILL CONTINUE INTO THE DAY SUNDAY AS
ANOTHER WEAK TROUGH TROUGH MOVES THROUGH IN THE NORTHWESTERLY FLOW.
BEST CHANCES FOR PRECIPITATION WILL CONTINUE TO BE OVER NORTHEASTERN
ALABAMA. THE GFS IS RATHER AGGRESSIVE WITH VERY STEEP LAPSE RATES
ALOFT. THE WEAK UPPER LEVEL FLOW AND LACK OF SURFACE FEATURE TO LIFT
PARCELS TO THEIR LFC WILL BE SUFFICIENT ENOUGH TO LIMIT STORM
SEVERITY AND EXPECT A STRONG STORM OR TWO WILL BE POSSIBLE AGAIN ON
SUNDAY AFTERNOON.

PRECIPITATION CHANCES SHOULD FINALLY BEGIN TO COME TO AN END ON
MONDAY AS UPPER LEVEL HEIGHTS INCREASE ACROSS THE SOUTHEAST.
TEMPERATURES ON MONDAY AND TUESDAY WILL PUSH UP INTO THE UPPER 80S
AND LOW 90S. RAIN CHANCES WILL RETURN DURING THE MIDDLE OF NEXT WEEK
AS MOISTURE INCREASES AHEAD OF AN UPPER LEVEL TROUGH. MODELS AT THIS
TIME APPEAR TO KEEP THE FRONT NORTH OF THE FORECAST AREA THROUGH THE
MIDDLE OF THE WEEK WITH A POSSIBLE FRONTAL PASSAGE LATER IN THE
WEEK.

05/MA

&&

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

&&

$$