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012
FXUS64 KBMX 210351
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
951 PM CST SAT DEC 20 2014

.UPDATE...
EVENING UPDATE.

&&

.DISCUSSION...

A SURFACE FRONT REMAINS NEAR THE GULF COASTAL INTERFACE THE NEXT
FEW DAYS. SEVERAL IMPULSES RIDE THROUGH THE SOUTHWESTERLY FLOW
ALOFT WITH A FEW WAVES DEVELOPING ALONG THE FRONT.

IN CENTRAL ALABAMA...CLOUDS COVERED MUCH OF THE SOUTHEASTERN HALF
OF THE AREA WITH HINTS AT MOVING SOUTHEASTWARD OVERNIGHT. BUT
AFTER SUNSET...THE CLOUDS HAVE ALMOST COMPLETELY HALTED AND
EVENTUALLY EXPECT THESE CLOUDS TO INCH BACK NORTHWARD IN RESPONSE
TO THE UPPER IMPULSES AND DEVELOPING ISENTROPIC LIFT. THIS CLOUD
GRADIENT WILL LEAD TO A RATHER LARGE TEMP GRADIENT OVERNIGHT. THE
CLEAR AREAS NORTHWEST SHOULD REACH THE UPPER 20S WHILE AREAS
SOUTHEAST REMAIN NEARLY STATIONARY WITH LOWS NEAR 50. THE
PROBLEMATIC AREA WILL BE RIGHT AT THE CLOUD NO CLOUD INTERFACE. IF
THE CLOUDS SLIDE SOUTHWARD SLIGHTLY...TEMPS WILL FALL ALONG THE
I-20 CORRIDOR...THEN STEADY OUT. GENERALLY WENT WITH THE IDEA THAT
THE CLOUDS MOVE VERY LITTLE BEFORE EVEN LOWER CLOUDS
REDEVELOP/MOVE NORTHWARD LATER TONIGHT. ADJUSTED TEMPS AND CLOUDS
FOR THESE TRENDS. WENT AHEAD AND MENTIONED SOME PATCHY FOG
AREAWIDE OVERNIGHT. DO NOT THINK THERE WILL BE MAJOR RESTRICTIONS
IN VISIBILITIES BUT FOG NONETHELESS FOR DIFFERING REASONS. HIGHER
LOW LEVEL MOISTURE SOUTH WILL HAVE TO BE MONITORED BECAUSE IF
TEMPS DO INDEED FALL A FEW DEGREES IT WILL BE CLOSE TO THE NON
MIXED CROSSOVER TEMP. NORTH...COOLER BUT NEAR SATURATED GROUND
CONDITIONS MAY CAUSE SOME FOG. UPDATES ALREADY OUT.

75

&&

.AVIATION...
00Z TAF DISCUSSION.

AS OF 00Z...CLEARING LINE OF CLOUDS HAD DROPPED AS FAR SOUTH AS
BHM AND GAD...AND HAD ALREADY GONE SOUTH OF TCL. STRONGLY SUSPECT
THAT THIS CLEARING LINE WILL CONTINUE TO MOVE SOUTHEAST...AT LEAST
TO EET...ANB AND ASN. BUT AT SOME POINT OVERNIGHT...ACCORDING TO
THE MODELS...THAT CLEARING LINE WILL STALL AND EVENTUALLY START TO
MOVE BACK TO THE NORTH AND WEST. ITS DOUBTFUL MGM GETS ANY
CLEARING TONIGHT...AND ALMOST A CERTAINTY CONDITIONS STAY IFR AT
TOI FOR THE DURATION. TRYING TO TIME THE RE-ARRIVAL OF THE CLOUDS
IN THE NORTHERN TAF LOCATIONS IS A BIT PROBLEMATIC.

/61/


&&

.PREV DISCUSSION...
/ISSUED 347 PM CST SAT DEC 20 2014/
SHORT TERM...TONIGHT THROUGH MONDAY.

ANOTHER CLOUDY AND DAMP DAY ACROSS AREAS ALONG AND SOUTH OF I-59
AS THE CLEARING LINE HAS NOT MADE MUCH PROGRESSION. THE CLOUDS ARE
BEGINNING TO ERODE ALONG THE I-59 CORRIDOR AND THIS TREND WILL
LIKELY CONTINUE THROUGH THE EARLY EVENING HOURS. CLOUDS WILL
LIKELY LINGER ACROSS THE SOUTHERN HALF OF CENTRAL ALABAMA TONIGHT
DUE TO A STALLED OUT FRONTAL BOUNDARY. A WEAK UPPER IMPULSE MOVING
ACROSS THE NORTHERN GULF OF MEXICO COULD TRIGGER SOME LIGHT
SHOWERS SOUTH OF I-85 LATER TONIGHT AND KEPT A SLIGHT CHANCE OF
RAIN.

THE LOW CLOUDS OVER SOUTH CENTRAL ALABAMA WILL SHIFT NORTHWARD ON
SUNDAY AS THE LOW LEVEL FLOW BECOMES SOUTHEAST...AND DO NOT EXPECT
TO SEE MUCH SUNSHINE ON SUNDAY. THE AIR MASS ABOVE 850MB WILL NOT
UNDERGO MUCH CHANGE THROUGH SUNDAY NIGHT WITH RELATIVELY DRY AIR
ACROSS NORTH ALABAMA...WITH DEEPER MOISTURE CONFINED TO THE
IMMEDIATE GULF COAST. RAIN CHANCES WILL EXPAND NORTHWARD ON MONDAY
TO INCLUDE ALL OF CENTRAL ALABAMA...BUT RAIN CHANCES WILL REMAIN
ON THE LOW SIDE.

LONG TERM...TUESDAY THROUGH SATURDAY.

A VIGOROUS UPPER LEVEL LOW WILL DROP SOUTHWARD FROM THE NORTHERN
PLAINS STATES AND DIG SOUTHWARD INTO TEXAS MONDAY NIGHT. THIS IS
BY FAR ONE OF THE MORE AMPLIFIED SYSTEMS THIS WINTER SEASON AND IT
WILL GENERATE A SOUTHERN SURFACE LOW THAT RAPIDLY DEEPENS AND
TRACKS NORTHEAST ACROSS ALABAMA AND TENNESSEE TUESDAY NIGHT.
DEEP SOUTHERLY FLOW WILL CREATE MUCH ABOVE NORMAL PRECIPITABLE
WATER PROFILES ACROSS ALABAMA TUESDAY AND TUESDAY NIGHT. WIDESPREAD
SHOWERS AND EMBEDDED THUNDERSTORMS WILL DEVELOP TUESDAY WELL AHEAD
OF THE SURFACE COLD FRONT. SURFACE DEWPOINTS IN THE LOWER 60S ARE
FORECAST TO ADVECT AS FAR NORTH AS THE I-20 CORRIDOR TUESDAY NIGHT
..AND DECENT MID LEVEL LAPSE RATES WILL CREATE ENOUGH INSTABILITY
TUESDAY NIGHT FOR CONVECTION. 0-6KM AND 0-1KM BULK SHEAR VALUES
ARE RELATIVELY HIGH AND CERTAINLY ENOUGH TO SUPPORT ROTATING
UPDRAFTS...AND STORM RELATIVE HELICITY VALUES ARE HIGH ENOUGH FOR
TORNADIC STORMS. THE PRIMARY LIMITING FACTOR WILL BE THE VERY
MOIST AIR MASS. WIDESPREAD SHOWERS ON TUESDAY COULD LIMIT INSTABILITY
AND SATURATED PROFILES WILL LIMIT UPDRAFT POTENTIAL. HOWEVER...COOL
SEASON SYSTEMS ARE NORMALLY HIGH SHEAR AND LOW INSTABILITY...AND
THIS SYSTEM IS VERY DYNAMIC AND STRENGTHENING AS IT CROSSES THE
MISSISSIPPI RIVER. THE MODELS ARE NOT IN GOOD AGREEMENT IN THE
PROGRESSION OF THE COLD FRONT. YESTERDAY THE GFS WAS FASTER THAN
THE ECMWF AND THEY HAVE FLIP FLOPPED TODAY.

THE COLD FRONT SHOULD BE NEAR THE ALABAMA AND GEORGIA STATE LINE
BY SUNRISE WEDNESDAY AND STRONG COLD AIR ADVECTION WILL ENSUE ON
WEDNESDAY. TEMPERATURES WILL LIKELY FALL WEDNESDAY MORNING...AND
STAY STEADY OR SLOWLY RISE WEDNESDAY AFTERNOON. THERE WILL BE
PLENTY OF WRAP AROUND MOISTURE ON WEDNESDAY AND EXPECT SCATTERED
LIGHT SHOWERS ACROSS THE NORTHERN HALF OF ALABAMA. THE CLOUDS WILL
CLEAR OUT CHRISTMAS EVENING AND CHRISTMAS DAY LOOKS GOOD WITH
MOSTLY CLEAR SKIES AND NEAR AVERAGE TEMPERATURES. A NORTHERN
STREAM SHORT WAVE TROF WILL PUSH A WEAK COLD FRONT TOWARDS ALABAMA
ON FRIDAY. A LINE OF SHOWERS ALONG THE FRONT COULD IMPACT CENTRAL
ALABAMA FRIDAY NIGHT AND SATURDAY.

58/ROSE

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     32  53  43  57  50 /  10  10  20  30  50
ANNISTON    38  55  46  58  51 /  10  20  30  30  40
BIRMINGHAM  37  56  46  60  54 /  10  10  20  30  40
TUSCALOOSA  34  59  46  61  53 /  10  10  20  30  40
CALERA      42  57  46  61  53 /  10  10  20  30  40
AUBURN      43  55  47  59  53 /  20  30  40  40  40
MONTGOMERY  46  59  48  65  55 /  20  30  40  30  40
TROY        48  57  49  64  56 /  20  40  40  30  40

&&

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

&&

$$








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