Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 221207
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
607 AM CST MON DEC 22 2014

.UPDATED...
AVIATION DISCUSSION.

&&

.DISCUSSION...

THE FORECAST OVER THE NEXT 48 HOURS IS VERY MESSY AND COMPLEX AS
A TROUGH BECOMES CARVED OUT ACROSS THE PLAINS STATES. THE FORECAST
AREA IS CURRENTLY NORTH OF A WARM FRONT DEVELOPING ALONG THE GULF
COAST. THIS BOUNDARY WILL MOVE NORTHWARD TODAY AS SOUTHERLY FLOW
STRENGTHENS IN RESPONSE TO AN UPSTREAM VORT MAX OVER THE SOUTHERN
PLAINS. TEMPERATURES ARE EXPECTED TO SLOWLY RISE INTO THE
AFTERNOON WITH ISENTROPIC LIFT NORTH OF THE WARM FRONT CAUSING
CLOUDS TO PERSIST. SOME SPOTTY LIGHT SHOWERS ARE POSSIBLE ACROSS
THE ENTIRE CWA AS THE WARM FRONT MAKES ITS MOVE NORTHWARD. SHORT
RANGE MODELS INDICATE THE BEST CHANCE FOR RAIN MAY BE ACROSS THE
NORTHWEST COUNTIES THIS AFTERNOON WHERE THE BEST LIFT MAY OCCUR.
THE OVERALL SETUP IS QUITE UNUSUAL WITH A LOW-AMPLITUDE TROUGH
TAKING SHAPE TO OUR NORTHWEST AND VERY COLD TEMPERATURES ALOFT.
ABUNDANT 925-800MB MOISTURE WILL COMBINE WITH STEEP UPPER-LEVEL
LAPSE RATES TO CREATE A CHANCE FOR A FEW ELEVATED THUNDERSTORMS
MAINLY ACROSS THE NORTHWEST. DEEP-LAYER SHEAR WILL BE SUFFICIENT
FOR ROTATING UPDRAFTS...SO IF ANY STORMS FORM...THEY COULD CONTAIN
SMALL HAIL.

AT THE SURFACE...A WEAKENING COLD FRONT IS FORECAST TO APPROACH
THE CWA OVERNIGHT AND EVENTUALLY STALL FROM NEAR HUNTSVILLE TO
MERIDIAN. THIS WILL CREATE A TEMPERATURE GRADIENT AND A BAROCLINIC
ZONE ON TUESDAY. MODELS SHOW A SURFACE LOW DEVELOPING IN THE
NORTHERN GULF AND TRAVELING NORTHEASTWARD ALONG THIS AXIS TUESDAY
NIGHT. AS THIS OCCURS...WIDESPREAD SHOWERS AND THUNDERSTORMS ARE
EXPECTED TO DEVELOP TUESDAY AFTERNOON. MODELS SUGGEST CONVECTION
MAY DEVELOP ALONG THE COASTAL BAROCLINIC ZONE WHICH MAY PREVENT
STORMS FROM BECOMING SURFACE BASED FARTHER NORTH. BEFORE THE
TROUGH BECOMES HIGHLY AMPLIFIED...A PLUME OF STEEPER MID-LEVEL
LAPSE RATES WILL BE PRESENT AND MAY ALLOW FOR A LOW END HAIL/WIND
THREAT WITH ISOLATED SUPERCELLS AND BOWING SEGMENTS. THIS THREAT
IS EXPECTED TO BE CONFINED TO AREAS NEAR AND SOUTH OF I-20 THROUGH
THE AFTERNOON. WITH ONLY MODEST LOW-LEVEL SHEAR THROUGH THE
AFTERNOON...THE TORNADO THREAT APPEARS MINIMAL ESPECIALLY IF
COASTAL CONVECTION CAUSES STORMS TO BECOME SLIGHTLY ELEVATED
ACROSS OUR AREA.

THOUGH LAPSE RATES WILL WEAKEN INTO TUESDAY NIGHT...A SMALL WINDOW
FOR A WEAK/BRIEF TORNADO OR TWO MAY OCCUR ACROSS THE SOUTHEASTERN
COUNTIES AS A SURFACE LOW DEEPENS ACROSS WEST ALABAMA AND MOVES
NORTHEAST. THIS THREAT WILL DEPEND ON THE EVOLUTION OF COASTAL
CONVECTION AND POSSIBLE ORGANIZATION OF A QLCS AS STRONGER FORCING
APPROACHES THE REGION.

THE GREATEST THREAT FROM THIS STORM SYSTEM COULD ACTUALLY END UP
BEING FLASH FLOODING ASSOCIATED WITH TRAINING THUNDERSTORMS.
WIDESPREAD 1 TO 2 INCH AMOUNTS ARE EXPECTED WITH A POTENTIAL FOR
3 TO 5 INCHES ACROSS THE SOUTHEAST COUNTIES. A FLASH FLOOD WATCH
COULD BECOME NECESSARY IF FORECAST CONFIDENCE INCREASES.

A COLD FRONTAL PASSAGE WILL BRING AN END TO THE RAIN WEDNESDAY
MORNING AS COLDER AIR MOVES IN. DRY AND COOL CONDITIONS WILL
PERSIST INTO THURSDAY AND FRIDAY BEFORE ANOTHER POTENTIAL SYSTEM
DEVELOPS FOR THE WEEKEND.

87/GRANTHAM

&&

.AVIATION...
12Z TAF DISCUSSION.

OVER THE NEXT 24 HOURS..NEAR STEADY STATE CONDITIONS OF IFR OR LIFR
ARE EXPECTED AT ALL TERMINALS WITH PERIODS OF SHOWERS POSSIBLE.
COMPUTER MODELS CONTINUE TO DEPICT A SATURATED LOW LEVEL AIR
MASS...WITH CEILINGS EXPECTED TO REMAIN WITHIN A COUPLE/FEW HUNDRED
FEET EITHER SIDE OF 1000 FT. THERE MAY BE LIMITED IMPROVEMENT DURING
THE DAYLIGHT HOURS. EXPECT CIGS/VIS TO LOWER AGAIN TONIGHT...WITH
PREDOMINANTLY LIFR CONDITIONS AT ALL TERMINALS. PERIODS OF SHOWERS
WILL BE POSSIBLE THIS AFTERNOON AS AN ELEVATED WARM FRONT LIFTS
NORTHWARD...AND AGAIN TONIGHT AS A COLD FRONT NEARS THE AREA AND
UPPER LEVEL FORCING INCREASES.

14

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     54  51  62  58  58 /  40  60 100 100  60
ANNISTON    55  52  64  60  61 /  40  50 100 100  60
BIRMINGHAM  57  56  64  56  56 /  40  60 100 100  50
TUSCALOOSA  59  58  65  52  53 /  50  60 100 100  30
CALERA      57  55  65  57  56 /  40  60 100 100  40
AUBURN      56  53  65  61  64 /  30  40 100 100  70
MONTGOMERY  61  58  70  62  62 /  40  40 100 100  50
TROY        62  58  69  63  63 /  40  40 100 100  60

&&

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

&&

$$

87/14







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