Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 211136 AAA
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
536 AM CST SUN DEC 21 2014

.UPDATE...
FOR 12Z AVIATION.

.DISCUSSION...

THIS MORNING`S WATER VAPOR IMAGERY SHOWS TWO UPPER LEVEL SHORTWAVES
ROTATING SOUTH AND EAST AROUND THE BROAD UPPER TROUGH OVER THE
CENTER OF THE CONUS. THE IMPULSE CURRENTLY OVER THE RIO GRANDE
REGION WILL SHIFT EAST/NORTHEAST TODAY AND HELP BRING A CHANCE OF
RAIN BACK TO THE EASTERN HALF OF THE FORECAST AREA LATER TODAY AND
TONIGHT. MEANWHILE AT THE SFC A VERY LOW STRATUS DECK HAS MOVED AS
FAR NORTH AS INTERSTATE 59 AND WILL LIKELY CONTINUE TO INCH
NORTHWEST AS ISENTROPIC LIFT INCREASES. NOT SURE IF ANYONE WILL SEE
THE SUN THIS AFTERNOON HAS OVERCAST SKIES SHOULD PERSIST THRU THE
DAY.

THE AFOREMENTIONED UPPER LEVEL IMPULSE WILL ALLOW A SFC LOW TO RIDE
NORTHEAST ALONG THE STALLED BOUNDARY JUST OFF THE COAST. ISO TO SCT
SHOWERS WILL BE POSSIBLE ACROSS THE EASTERN PORTIONS OF THE CWA
TODAY AND TONIGHT WITH ONLY LIGHT ACCUMULATIONS. WEDGING ALONG THE
ATLANTIC SEABOARD BUILDS INTO THE STATE ON MONDAY WITH SOUTHEASTERLY
SFC WINDS. LOW LEVEL MOISTURE WILL CONTINUE TO RISE AND SCT SHOWERS
WILL BE POSSIBLE AREA WIDE DURING THE DAY.

MOISTURE REALLY BEGINS TO SURGE NORTHWARD MONDAY NIGHT AS SFC WINDS
TURN TO THE SOUTH IN RESPONSE TO A DEVELOPING LOW PRESSURE SYSTEM TO
THE WEST. THE UPPER TROUGH OVER THE CENTER OF THE COUNTRY WILL
DEEPEN AS A SHORTWAVE EMERGES ON THE LEE SIDE OF THE ROCKIES AND
DIVES SOUTHWARD INTO THE TEXAS. THIS WILL GENERATE A SFC LOW NEAR
THE TEXAS COAST THAT WILL TRACK NORTHEAST ACROSS MS/AL LATE TUESDAY
AND THEN INTO THE OHIO VALLEY ON WEDNESDAY. IN GENERAL MODELS HAVE
SLOWED THE SYSTEM DOWN A BIT FROM YESTERDAY...BUT THERE ARE STILL
SLIGHT DISCREPANCIES IN THE ACTUAL TRACK OF THE SFC LOW DUE TO
DIFFERENCES IN THE UPPER LEVEL PATTERN. OVERALL KEPT MUCH OF THE
PREVIOUS FORECAST IN TACT WITH SOME INCREASE TO POPS IN THE TUE
NIGHT/WED TIME FRAME DUE TO THE SLOWER PROGRESSION OF THE SYSTEM.

NOW TO THE SEVERE THREAT. WITH SUFFICIENT SHEAR AND UPPER DYNAMICS
THE POTENTIAL IS STILL THERE...BUT SOME RESERVATIONS LINGER...MAINLY
IN RELATION TO THE INSTABILITY. THERE ARE TWO FACTORS THAT COULD
LIMIT (PERHAPS RATHER SIGNIFICANTLY) THE DESTABILIZATION OVER
CENTRAL ALABAMA ON TUESDAY. FIRST...WIDESPREAD ISENTROPIC ASCENT
WILL LEAD TO THE DEVELOPMENT OF SHOWERS AND SOME ELEVATED
THUNDERSTORMS MONDAY NIGHT INTO TUESDAY MORNING. SECOND...GUIDANCE
HAS BEEN CONSISTENT IN DEPICTING A COMPLEX OF SHOWERS/STORMS
ALONG/SOUTH OF A FRONTAL BOUNDARY NEAR THE COAST. THIS WOULD
EFFECTIVELY CUT CENTRAL ALABAMA OFF FROM THE RICHER AIRMASS OVER THE
GULF WATERS. BUT...IF THE ATMOSPHERE CAN SOMEHOW DESTABILIZE ENOUGH
BY TUESDAY AFTERNOON THEN THERE WILL BE AT LEAST A THREAT OF
DAMAGING WINDS AND PERHAPS A TORNADO...WITH THE GREATEST THREAT
BEING ACROSS THE SOUTHWEST COUNTIES. WITH ALL THIS BEING SAID WILL
MAINTAIN LOW CONFIDENCE OF SEVERE IN HWO BUT WILL BACK OFF ON
WORDING SLIGHTLY. THIS SYSTEM BEARS CLOSE WATCHING AND CHANGES TO
THE THREATS AND THREAT AREA ARE POSSIBLE OVER THE NEXT DAY OR TWO.

THE COLD FRONT SHOULD EXIT THE FORECAST AREA BY WEDNESDAY AFTERNOON
WITH SOME SHOWERS LINGERING THRU THE AFTERNOON...MAINLY IN THE
NORTH/EAST. BASED ON SOUNDING PROFILES...THE COLUMN DRIES
SUFFICIENTLY BEFORE THE COLDER AIR ARRIVES. NOT LOOKING AT A
SIGNIFICANT COOL DOWN BEHIND THIS SYSTEM THOUGH. HIGHS WILL STAY
GENERALLY IN THE 50S ON WEDNESDAY WITH LOWS IN THE 30S. TEMPS
REBOUND QUICKLY BEGINNING THURSDAY AS SFC WINDS SHIFT BACK TO THE SW
THEN S AHEAD OF THE NEXT SYSTEM...WHICH WILL BRING RAIN CHANCES BACK
TO THE FORECAST AREA IN THE FRI/SAT TIME FRAME.

19

&&

.AVIATION...
12Z TAF DISCUSSION.

IT IS GOING TO BE TOUGH DEALING WITH THE CLOUDS OVER THE NEXT 24
HOURS. CONDITIONS AT 12Z RANGED FROM JUST ABOVE MVFR AT TCL AND
BHM...TO IFR AT TOI. IN BETWEEN THE TWO EXTREMES...CONDITIONS WERE
GENERALLY MVFR WITH IFR CONDITIONS INTERSPERSED. BHM AND TCL ARE ON
THE NORTHERN EDGE OF THE MVFR TO OCNL IFR CIGS SO BELIEVE CONDITIONS
WILL OSCILLATE AT THESE TWO SITES AND FINALLY LEVEL OUT WITH MVFR
CIGS PREVAILING BY MID TO LATE MRNG. OTHERWISE THERE WILL LIKELY BE
LITTLE TO NO BREAKS IN THE CURRENT CONDITIONS TODAY...WITH MODEL
SOUNDINGS INDICATING SOME INCREASE IN CIG HEIGHTS BY MID DAY BUT
THEN A GENERAL LOWERING OF CIGS TO IFR CONDITIONS BY OR AFTER 06Z.
SURFACE WINDS SHOULD REMAIN HIGH ENOUGH TO PRECLUDE ANY MORE THAN
GENERALLY MFVR VSBYS LATE TONIGHT.

/41/

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     53  44  56  52  61 /  20  30  30  50  90
ANNISTON    55  47  57  52  62 /  20  30  30  50  90
BIRMINGHAM  56  47  59  57  64 /  10  20  30  50  90
TUSCALOOSA  59  47  61  56  66 /  10  10  30  50  90
CALERA      57  47  60  56  65 /  10  20  30  50  90
AUBURN      55  48  57  56  67 /  30  40  40  50  90
MONTGOMERY  59  49  63  58  68 /  20  30  30  50  90
TROY        57  50  62  59  68 /  30  40  40  50  90

&&

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

&&

$$









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