754 
FXUS64 KBMX 231812
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
1212 PM CDT SAT MAR 23 2013

.UPDATE...
FOR 18Z AVIATION DISCUSSION.

&&

.DISCUSSION...

THE WAITING GAME HAS BEGUN IN RELATION TO WHEN THE WARM FRONT WILL
BEGIN ITS NORTHWARD TREK. BASED ON SURFACE ANALYSIS...THE WARM
FRONT IS CURRENTLY STRETCHING FROM CENTRAL LOUISIANA EAST
SOUTHEASTWARD TO JUST ALONG THE FLORIDA GULF COAST. WE WILL BE
WATCHING THE DEVELOPMENT OF THE SURFACE LOW ACROSS CENTRAL
LOUISIANA LATER ON THIS AFTERNOON AND EVENING...AS THE STRENGTH OF
THAT LOW WILL HAVE A LARGE IMPACT ON HOW FAR NORTH THE WARM FRONT
WILL BE ALLOWED TO MOVE. SURFACE ANALYSIS ALSO INDICATES SOME
SURFACE RIDGING ONGOING JUST TO OUR WEST...AS WELL AS WHAT LOOKS
LIKE A WEAK BOUNDARY STRETCHING FROM NORTHERN MISSISSIPPI ACROSS
CENTRAL ALABAMA. SHOWERS HAVE DEVELOPED ALONG THIS BOUNDARY 
THROUGHOUT THE MORNING. WIDESPREAD HEAVIER SHOWERS HAVE ALREADY 
BEGUN TO DEVELOP ALONG THE MAIN WARM FRONT ACROSS SOUTHERN
MISSISSIPPI...AND THAT'S WHAT WE WILL HAVE TO WATCH FOR INTO THE
LATE AFTERNOON HOURS FOR THE POSSIBILITY OF ELEVATED SEVERE STORMS
DEVELOPING THAT CAN PRODUCE LARGE HAIL AND DAMAGING STRAIGHT-LINE
WINDS.

THE IMPULSE THAT AFFECTED THE NORTHERN HALF OF CENTRAL ALABAMA
THIS MORNING HAS SINCE RAPIDLY MOVED EASTWARD THROUGH GEORGIA...WITH 
EASTERLY TO SOUTHEASTERLY SURFACE FLOW DOMINATING ACROSS OUR AREA. 
THE EASTERLY WEDGE WILL CONTINUE THROUGH THIS AFTERNOON...AND IS 
ALREADY CAUSING ALL KINDS OF PROBLEMS FOR MODEL GUIDANCE. ISENTROPIC 
UPGLIDE DUE TO THE SOUTHWESTERLY FLOW ALOFT RISING UP AND OVER THE 
COOL LAYER AT THE SURFACE IS CONTINUING TO PRODUCE WIDESPREAD CLOUD 
COVER. IF THE WEDGE HOLDS FIRM...WE WILL HAVE A VERY DIFFICULT TIME 
MIXING THOSE CLOUDS OUT. MODEL GUIDANCE IS PRESENTING THAT MIXING 
COULD OCCUR ACROSS OUR SOUTHWEST COUNTIES THIS AFTERNOON WHICH COULD 
LEAD TO TEMPERATURES IN THE UPPER 60S TO LOWER 70S FOR THOSE 
AREAS...BUT MODELS ALREADY AT LEAST 5-7 DEGREES OFF FROM CURRENT 
TEMPERATURES. LOOKING AT THE KBMX RAOB FROM 06Z THIS MORNING...GOOD 
LAPSE RATES ALOFT WILL STILL OFFER THE POSSIBILITY OF THUNDERSTORM 
DEVELOPMENT ONCE THE WARM FRONT STARTS TO MOVE OUR WAY. MOST 
UNSTABLE CAPES ARE ALREADY ABOVE 1000J/KG ACROSS OUR SOUTHWESTERN 
COUNTIES BASED ON RAP ANALYSIS...WITH 0-6KM BULK SHEAR VALUES OF 
70-80 KNOTS...SO WHEN PARCELS ARE LIFTED UP AND OVER THE WARM FRONT 
THEY SHOULD HAVE NO PROBLEM FORMING STRONG TO SEVERE THUNDERSTORMS.

IN TERMS THE FORECAST FOR THE REST OF THE AFTERNOON...HAVE GONE AHEAD
AND REDUCED POPS AREAWIDE AND ONLY MENTIONED CHANCE SHOWERS WITH
SLIGHT CHANCE THUNDER FOR THE REMAINDER OF THE DAY ACROSS ALL OF
CENTRAL ALABAMA. I ALSO LOWERED HIGHS ACROSS THE BOARD...MORE SO
FOR OUR SOUTHERN LOCATIONS...THAT WILL STRUGGLE TO WARM INTO THE
UPPER 60S DUE TO THE WARM FRONT STILL REMAINING TO OUR SOUTH AND
ISENTROPIC LIFT CONTINUING TO DEVELOP WIDESPREAD CLOUD COVER. WE
WILL CONTINUE TO WATCH MESOSCALE TRENDS THROUGH THE REST OF THE
AFTERNOON AND WILL COVER THE ENTIRE EVENT IN DETAIL WITH THE
AFTERNOON FORECAST PACKAGE. UPDATES ARE OUT.

56/GDG

&&

.AVIATION...
18Z TAF DISCUSSION.

MVFR CIGS CONTINUE ACROSS MOST OF CENTRAL ALABAMA THIS AFTERNOON. 
SHOWERS AND STORMS ARE DEVELOPING OFF TO OUR SOUTH...AND WILL 
CONTINUE MOVING NORTHWARD THROUGHOUT THE REST OF THE AFTERNOON AND 
EVENING. FOR OUR SOUTHERN SITES AT KMGM AND KTOI...WENT AHEAD KEPT 
TSRA FOR THE AFTERNOON AND EVENING WITH THE BEST CHANCE OF 
WIDESPREAD THUNDERSTORMS ACROSS SOUTHERN ALABAMA. ELSEWHERE...WENT 
WITH VCTS WITH RA FOR THE REMAINING TAF SITES THROUGH THE OVERNIGHT 
HOURS...BUT BASED ON THUNDERSTORM DEVELOPMENT...AMENDMENTS WILL BE 
NEEDED THROUGHOUT THE NIGHT. RAPID REDUCTIONS IN CIGS AND VIS WILL 
ACCOMPANY ANY STORM THAT PASSES OVER A TERMINAL LOCATION. WINDS WILL 
CONTINUE FROM THE EAST...AND SHIFTING TO THE SOUTHEAST THROUGHOUT 
THE EVENING.

56/GDG

&&

.PREV DISCUSSION... /ISSUED 642 AM CDT SAT MAR 23 2013/ 

SHORT TERM...TODAY THROUGH SUNDAY NIGHT.

AN UPPER LEVEL IMPULSE MOVING THROUGH ARKANSAS HAS BEEN PRODUCING
A CLUSTER OF THUNDERSTORMS ACROSS NORTHERN MISSISSIPPI. THE STORMS
ARE ELEVATED AS SURFACE TEMPERATURES ARE CURRENTLY IN THE 40S
ACROSS NORTHERN MISSISSIPPI AND ALABAMA. A FEW OF THE STORMS COULD
PRODUCE LARGE HAIL ACROSS NORTHWEST ALABAMA EARLY THIS MORNING DUE
TO 500MB TEMPS NEAR -18 CELSIUS. THIS CLUSTER OF STORMS WILL
AFFECT AREAS ALONG AND NORTH OF I-20 THRU THE MID MORNING HOURS.
FARTHER TO THE SOUTH THE PRIMARY FORCING MECHANISM FOR CONVECTION
TODAY WILL LIKELY BE DIURNAL HEATING...WHICH MEANS ANY CONVECTION
WILL BE MAINLY DURING THE AFTERNOON HOURS. THE SURFACE WARM FRONT
AND MORE UNSTABLE AIR MASS WILL STAY SOUTH OF CENTRAL ALABAMA THIS
AFTERNOON...AND ANY SEVERE STORMS WILL BE CONFINED TO THE EXTREME
SOUTHERN COUNTIES.

THE MODELS ARE STILL STRUGGLING TO BRING THE SURFACE WARM FRONT
NORTHWARD TONIGHT DUE TO WEAK SURFACE CYCLOGENESIS WEST OF ALABAMA.
THE TORNADO THREAT IS TIED TO THE LOCATION OF THE WARM FRONT AND
SO THE THREAT AREA WILL REMAIN CONFINED TO THE SOUTHERN HALF OF
CENTRAL ALABAMA. NORTH OF THE WARM FRONT...THE PRIMARY THREAT WILL
LIKELY BE LARGE HAIL...AS THE SURFACE BASED LIFTED INDICES STAY
POSITIVE FOR MOST OF THE NIGHT...WITH ANY INSTABILITY ELEVATED
ABOVE THE BOUNDARY LAYER. SUNDAY IS LOOKING MORE INTERESTING AS
THE SURFACE FRONT PUSHES THROUGH THE AREA. SURFACE TEMPERATURES
WILL WARM INTO THE MIDDLE 60S TO MIDDLE 70S ACROSS EAST ALABAMA.
COMBINED WITH COLD TEMPERATURES ALOFT...LIFTED INDICES ARE
FORECAST TO FALL TO THE -5 TO -7 CELSIUS RANGE...WITH SURFACE
BASED CAPE VALUES AROUND 1500 J/KG. MOISTURE WILL BE LIMITED AS
PRECIPITABLE WATER VALUES FALL BELOW ONE INCH...BUT ANY STORMS
THAT CAN GET GOING COULD PRODUCE LARGE HAIL. A THIS TIME...WILL
NOT MENTION SEVERE STORMS FOR SUNDAY...BUT IT IS SOMETHING THAT
WILL NEED TO BE MONITORED IN FUTURE OUTLOOKS.

SURFACE WINDS WILL INCREASE OUT OF THE WEST SUNDAY AFTERNOON AS
THE PRESSURE GRADIENT INCREASES ON THE BACK SIDE OF THE EXITING
SURFACE LOW...AND A WIND ADVISORY WILL LIKELY BE REQUIRED IN LATER
FORECASTS.

58/ROSE

LONG TERM...MONDAY THROUGH FRIDAY.

A MUCH COLDER AIR MASS WILL OVERSPREAD CENTRAL ALABAMA FOR THE
FIRST HALF OF THE WORK WEEK. MONDAY AND TUESDAY WILL BE THE
COLDEST DAYS OF THE WEEK WITH HIGH TEMPERATURES 15-20 DEGREES
BELOW AVERAGE. SOME AREAS ACROSS NORTH ALABAMA MAY NOT GET OUT OF
THE 40S FOR DAYTIME HIGHS. LOW TEMPERATURES WILL ALSO FALL TO NEAR
OR JUST BELOW FREEZING TUESDAY AND WEDNESDAY MORNINGS FOR A LARGE
PORTION OF CENTRAL ALABAMA. SKIES WILL BE MOSTLY CLEAR DURING THE
WEEK...BUT A DECK OF LOWER CLOUDS WILL LIKELY ADVECT INTO NORTH
ALABAMA MONDAY NIGHT AND TUESDAY MORNING...AND WOULD NOT BE
SURPRISED TO SEE A FEW SNOW FLURRIES. A NICE WARM-UP BY THE END OF
THE WEEK WITH HIGHS IN THE UPPER 60S TO LOWER 70S BY FRIDAY.

58/ROSE

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     55  50  63  35  48 /  50 100  60  10  10 
ANNISTON    58  52  68  35  49 /  50 100  60  10  10 
BIRMINGHAM  60  53  65  34  50 /  50 100  50  10  10 
TUSCALOOSA  61  55  67  35  52 /  50 100  30  10  10 
CALERA      60  55  67  36  51 /  50 100  40  10  10 
AUBURN      59  55  72  37  52 /  40 100  60  10  10 
MONTGOMERY  62  61  75  38  55 /  40 100  40  10  10 
TROY        65  61  75  38  54 /  40 100  40   0  10 

&&

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

&&

$$

56/58