Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 222212
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
412 PM CST MON DEC 22 2014

.SHORT TERM...
TONIGHT THROUGH TUESDAY.

CHALLENGING FORECAST REMAINS AHEAD OF US AS A VERY DYNAMIC SYSTEM
TAKES SHAPE OVERNIGHT TONIGHT AND MOVES THROUGH CENTRAL ALABAMA
TUESDAY NIGHT THROUGH THE DAY ON WEDNESDAY. FIRST...LOTS OF ACTIVITY
ON RADAR THIS AFTERNOON ASSOCIATED MAINLY FROM TWO FACTORS. THE
FIRST IS ISENTROPIC LIFT AND AHEAD OF THE WARM FRONT TO OUR SOUTH
THAT IS CURRENTLY LOCATED ALONG THE GULF COAST. THE SECOND IS DUE TO
LIFT FROM A SHORTWAVE ROTATING AROUND THE BASE OF THE LONGWAVE
TROUGH CURRENTLY LOCATED IN THE ARKLATEX. STEEP LAPSE RATES ALOFT
HAVE ACTUALLY ALLOWED FOR A FEW ELEVATED UPDRAFTS. NICKEL SIZE HAIL
WAS REPORTED IN LOWNDES COUNTY...AND A FEW MORE SMALL HAIL PRODUCERS
WON`T BE OUT OF THE QUESTION THROUGH THE REST OF THE AFTERNOON AND
EVENING WITH 500MB TEMPERATURES AROUND -17 TO 18C.

AS THE WARM FRONT CONTINUES TO LIFT NORTHWARD OVERNIGHT
TONIGHT...TEMPERATURES SHOULD RISE WITH WARM AIR ADVECTION ON THE
INCREASE. SHOWERS WITH A FEW STORMS WILL CONTINUE TO BE SCATTERED TO
NUMEROUS IN NATURE. THE BEST CHANCE OF MORE WIDESPREAD RAIN APPEARS
TO BE IN THE NORTHERN HALF OF CENTRAL ALABAMA TONIGHT AS THE BEST
LIFT SHOULD REMAIN NORTH OF THE WARM FRONT.

TAKING A LOOK AT THE HIGHLY ADVERTISED SYSTEM COMING THROUGH ON
TUESDAY AND WEDNESDAY...IT NOW APPEARS THAT THE GREATEST IMPACT FROM
THIS SYSTEM MAY BE HEAVY RAINFALL MORE THAN SEVERE STORMS. PWATS
ADVERTISED FROM 1.6 TO 1.7 INCHES ARE CLOSE TO THE 99TH PERCENTILE
IF YOU LOOK AT PW CLIMATOLOGY. FORECAST SOUNDINGS ALSO INDICATE
THAT THUNDERSTORMS WILL BE QUITE PROFICIENT RAINFALL PRODUCERS WITH
TALL SKINNY CAPE PROFILES AND PLENTY OF DIVERGENCE ALOFT TO SUSTAIN
UPDRAFTS. ALTHOUGH WE`VE BEEN RELATIVELY DRY SO FAR THIS FALL AND
ARE STILL UNDER DROUGHT CATEGORIES...WE`RE CONCERNED ABOUT TRAINING
THUNDERSTORMS GIVEN THE CONTINUED SOUTHWESTERLY FLOW ALOFT AND
ADDITIONAL STORMS EXPECTED TO DEVELOP FROM TONIGHT THROUGH WEDNESDAY
MORNING. WE`RE GOING TO GO AHEAD AND ISSUE A FLASH FLOOD WATCH FOR
GENERALLY OUR SOUTHEASTERN COUNTIES WHERE CONFIDENCE OF RAINFALL
AMOUNTS OF 2.5 TO 3 INCHES IS THE HIGHEST. LOCALIZED AMOUNTS OF UP
TO 4 INCHES CAN BE POSSIBLE WHERE STORMS MOVE REPEATEDLY OVER THE
SAME AREAS. WE`LL CLOSELY MONITOR ONGOING TRENDS TO SEE IF THE WATCH
AREA WOULD NEED TO BE EXPANDED NORTHWARD IF NECESSARY.

GETTING INTO THE DETAILS ABOUT THE SEVERE WEATHER THREAT...IT
APPEARS THE OVERALL THREAT SHOULD REMAIN RATHER LIMITED WITH THIS
SYSTEM. THE AMOUNT OF CLOUDS AND WIDESPREAD RAINS THAT HAVE BEEN
CONSISTENTLY ADVERTISED WILL BE THE BIG FACTOR TO HELP PREVENT MORE
WIDESPREAD SEVERE STORMS TO DEVELOP. AS SHOWERS AND STORMS DEVELOP
ALONG THE GULF COAST...THE BEST MOISTURE AND INSTABILITIES ARE
EXPECTED TO STAY SHUNTED OFF TO THE SOUTH. GIVEN THE DYNAMIC NATURE
OF THIS SYSTEM...WE`RE STILL GOING TO HIGHLIGHT THE LOW-CONFIDENCE
SEVERE THREAT GENERALLY ALONG AND SOUTH OF I-20 STARTING TUESDAY
AFTERNOON THROUGH EARLY TUESDAY EVENING...THEN SHIFTING FARTHER
SOUTHEAST DURING THE OVERNIGHT AND EARLY MORNING HOURS ON
WEDNESDAY. DURING THIS TIMEFRAME THE 850MB JET REALLY CRANKS UP TO
AROUND 50 KNOTS TUESDAY EVENING AND REMAINS AROUND 40 KNOTS
OVERNIGHT INTO WEDNESDAY MORNING. WITH THE CURRENT INSTABILITY
VALUES THAT ARE EXPECTED...A LOW THREAT OF SEVERE STORMS WILL BE
POSSIBLE. AN ISOLATED WEAK TORNADO CAN`T BE RULED OUT...ALONG WITH
A FEW DAMAGING WIND GUSTS. OF COURSE...IF MORE INSTABILITY CAN BE
REALIZED WE MIGHT BE LOOKING AT A DIFFERENT SITUATION AND WE`LL
CONTINUE TO ANALYZE THE LATEST TRENDS AS THEY EVOLVE. SURPRISES
CAN OCCUR WITH THESE COLD SEASON DYNAMIC SYSTEMS.

56/GDG

.LONG TERM...
WEDNESDAY THROUGH MONDAY...

RAINFALL BEGINS TO PUSH OUT OF THE AREA ON WEDNESDAY MORNING WITH
SHOWERS ENDING ACROSS EAST ALABAMA BEFORE NOON. THE HIGH TEMPERATURE
WILL COME IN THE MORNING WITH COOLING TEMPERATURES THROUGH THE DAY.
CHRISTMAS DAY LOOKS COOL BUT DRY WITH MORNING LOWS IN THE 30S AND
AFTERNOON TEMPS IN THE 48 TO 53 RANGE.

WARMER FRIDAY AND SATURDAY BUT A FAST MOVING SHORTWAVE WILL APPROACH
THE SOUTHEAST SATURDAY EVENING WITH A CHANCE OF RAIN LATE SATURDAY
THROUGH SUNDAY. WENT WITH A GENERAL EURO/CANADIAN BLEND...
HOWEVER...THERE IS SOME CONSIDERABLE SPREAD FROM THE 12Z MODELS ON
THIS FEATURE AND DETAILS WILL HAVE TO BE WORKED OUT A LITTLE LATER
IN THE WEEK.

JUST BEYOND THE FORECAST PERIOD...ANOTHER ROUND OF HEAVY RAIN MAY BE
POSSIBLE THROUGH THE MIDDLE OF NEXT WEEK.

88

&&

.AVIATION...
18Z TAF DISCUSSION.

IFR CONDITIONS WILL PREVAIL THROUGH THE NEXT 24 HOURS. CEILINGS
WILL BE THE MAIN ISSUE. WHILE AN OCCASIONAL BREAKOUT TO MVFR WILL
BE POSSIBLE...THE MAJORITY WILL BE IFR. SOME LIFR IS ALSO EXPECTED
OVERNIGHT. FOR THE WEATHER...PERIODS OF RAIN WILL CONTINUE FOR MGM
AND TOI WITH MORE PATCHY RAIN ACROSS THE NORTH...THROUGH 00Z.
WINDS GENERALLY FROM THE SOUTHEAST AT 5 TO 10 KTS.

88

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     52  60  57  59  38 /  60 100 100  60  10
ANNISTON    52  62  59  61  38 /  60 100 100  60  10
BIRMINGHAM  56  64  58  59  38 /  60 100 100  50  10
TUSCALOOSA  58  66  56  57  38 /  60 100 100  40  10
CALERA      55  65  58  59  38 /  60 100 100  50  10
AUBURN      54  63  60  62  39 /  50 100 100  80  10
MONTGOMERY  59  69  61  62  38 /  40 100 100  50  10
TROY        59  68  61  63  39 /  40 100 100  70  10

&&

.BMX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM TUESDAY MORNING THROUGH LATE TUESDAY
NIGHT FOR THE FOLLOWING COUNTIES: AUTAUGA...BARBOUR...BULLOCK...
ELMORE...LEE...LOWNDES...MACON...MONTGOMERY...PIKE...RUSSELL.

&&

$$






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