Area Forecast Discussion
Issued by NWS Birmingham, AL

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000
FXUS64 KBMX 210021
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
621 PM CST THU NOV 20 2014

.UPDATE...
FOR 00Z AVIATION.

&&

.DISCUSSION...

DRY WEATHER IS FORECAST TO CONTINUE THROUGH THE REST OF THE WORK
WEEK...WITH SURFACE HIGH PRESSURE REMAINING IN CONTROL. THE
PRIMARY FOCUS FOR THIS FORECAST PACKAGE REMAINS THE STORM SYSTEM
FORECAST TO BRING AMPLE RAIN AND A CHANCE OF THUNDERSTORMS
SATURDAY NIGHT INTO SUNDAY.

WHILE THE MODELS ARE IN GOOD AGREEMENT ON THE GENERAL IDEA OF RAIN
OVERSPREADING THE AREA SATURDAY NIGHT...THERE ARE STILL SOME
IMPORTANT DETAILS THAT WE REALLY NEED TO START HASHING OUT. THE
UPPER LEVEL PATTERN...WITH A PROGRESSIVE SHORTWAVE TROUGH BECOMING
NEGATIVELY TILTED AS IT LIFTS NORTHEASTWARD TO OUR WEST...IS ONE
THAT USUALLY CAUSES A RED FLAG TO GO UP TO AT LEAST INVESTIGATE
FOR THE POSSIBILITY OF SEVERE. AND WHILE CONFIDENCE IN THE SEVERE
WEATHER POTENTIAL IS STILL LOW...IT IS SOMETHING THAT I STILL
THINK REMAINS A POSSIBILITY.

PREVIOUS DISCUSSIONS HAVE MENTIONED THE LOW LEVEL WIND TRAJECTORY
AHEAD OF THE SYSTEM (LARGELY EAST TO SOUTHEAST)...AND HOW THAT
WILL MAKE IT HARD TO GET THE BEST MOISTURE (HIGHER DEWPOINTS) INTO
CENTRAL ALABAMA. A BIG WARM FRONTAL RAIN SHIELD WONT HELP MATTERS
IN THAT REGARD EITHER. BUT RIGHT BEFORE THE INITIAL DRY LINE MOVES
THROUGH (AND THE UPPER SHORTWAVE LIFTS WELL TO OUR NORTH)...THERE
IS A SHORT TIME WHEN WINDS COME MORE DIRECTLY OUT OF THE SOUTH.
WILL THAT BE ENOUGH TO ALLOW DEWPOINTS TO GET HIGH ENOUGH TO
SUPPORT VIGOROUS SURFACE BASED THUNDERSTORMS? TOO HARD TO TELL
RIGHT NOW...BUT I WOULD SAY THE CHANCE IS NON-ZERO.

THE LAST COUPLE RUNS OF THE NAM LENDS SOME SUPPORT TO THIS IDEA.
ITS SLOWED DOWN SOLUTION SUGGESTS THERE MAY BE A TIME GAP BETWEEN
THE INITIAL SURGE OF RAIN SATURDAY NIGHT AND ANOTHER ROUND OF MORE
CONVECTIVE WEATHER ON SUNDAY. IN FACT...IF THE TIMING ON THE NAM
SLOWS DOWN MUCH MORE...WE COULD BE GETTING INTO A PEAK HEATING
SCENARIO AS THE DRY LINE (OR WHATEVER) MOVES IN FROM THE WEST
SUNDAY AFTERNOON. I GUESS THIS IS ALL JUST A LONG WINDED WAY OF
SAYING THAT...WHILE IT APPEARS THAT THE CURRENT MODEL CONSENSUS
SUGGESTS THAT THE SEVERE THREAT THIS FAR NORTH WOULD BE MINIMAL
(OR NON- EXISTENT)...THERE IS AT LEAST ONE (PLAUSIBLE) SCENARIO
THAT EQUALLY SUGGESTS THAT SEVERE STORMS (INCLUDING A TORNADO
THREAT) COULD BECOME A POSSIBILITY.

A RETURN TO COLDER AND DRIER AIR IS FORECAST TO RUSH IN BEHIND THE
MAIN COLD FRONT...WHICH SHOULD ARRIVE HERE SUNDAY NIGHT INTO
MONDAY. MOS GUIDANCE IS HOLDING ON TO CHANCE/SLIGHT CHANCE POPS
THROUGH THE MIDDLE OF THE WEEK...WITH MORE SHORTWAVE ENERGY
ROUNDING THE BASE OF THE MEAN UPPER LEVEL EASTERN STATES TROUGH.
MY GUT SAYS THAT THE MODELS TYPICALLY CLEAR THINGS OUT TOO QUICKLY
BEHIND SYSTEMS SUCH AS THIS...BUT ALSO TEND TO HOLD ONTO SMALL
POPS TOO LONG AS WELL.

/61/

&&

.AVIATION...
00Z TAF DISCUSSION.

VFR CONDITIONS WILL PREVAIL THROUGH MUCH OF THE EVENING AND
OVERNIGHT HOURS TONIGHT. BROKEN MID-LEVEL CLOUD COVER WILL
CONTINUE TO MOVE INTO THE STATE FROM THE WEST. MVFR CIGS ARE
POSSIBLE AFTER 06Z TONIGHT THROUGH FRIDAY MORNING FOR MANY OF THE
NORTHERN TERMINALS. MEANWHILE...PATCHY FOG WILL BE POSSIBLE ACROSS
THE SOUTHERN TERMINALS OF KMGM AND KTOI OVERNIGHT. AT LEAST MVFR
VIS IS POSSIBLE AND WILL MONITOR TRENDS CLOSELY OVERNIGHT FOR ANY
WIDESPREAD FOG DEVELOPMENT. EASTERLY SURFACE WINDS WILL TRANSITION TO THE
SOUTHEAST DURING THE DAY ON FRIDAY.

56/GDG

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     32  57  37  59  50 /   0   0   0  10  90
ANNISTON    35  59  38  59  50 /   0   0   0  10  90
BIRMINGHAM  38  60  42  62  54 /   0   0   0  10  90
TUSCALOOSA  40  64  44  64  56 /  10  10  10  10 100
CALERA      39  62  41  62  54 /   0   0   0  10  90
AUBURN      39  62  42  61  52 /   0   0   0  10  90
MONTGOMERY  37  66  41  65  55 /   0   0   0  10  90
TROY        37  64  42  65  57 /   0   0   0  10  90

&&

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

&&

$$



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