Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 232040
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
340 PM CDT WED JUL 23 2014

.DISCUSSION...

ANTICIPATE SEVERAL UNUSUAL FEATURES WILL IMPACT CENTRAL ALABAMA
THROUGH THE END OF THIS FORECAST PERIOD. ALOFT AN UPPER LEVEL LOW
STILL EVIDENT ON WATER VAPOR SATELLITE IMAGERY OVER SOUTHERN
MISSISSIPPI AND SOUTHEASTERN LOUISIANA CONTINUES TO RETROGRADE
SLOWLY TO THE SOUTHWEST WHILE WEAKENING. SCATTERED SHOWERS AND
THUNDERSTORMS HAVE FORMED ONCE AGAIN THIS AFTERNOON...MAINLY ACROSS
THE NORTHWESTERN HALF OF THE AREA...AND TO THE EAST OF THIS UPPER
LOW AS PLENTIFUL LOW LEVEL MOISTURE REMAINS IN PLACE. LOOKING OVER
THE CONUS...A LARGE CLOSED UPPER RIDGE REMAINS CENTERED OVER THE
ROCKIES OUT WEST...AND AN UPPER TROUGH IS LOCATED OVER THE GREAT
LAKES REGION AND ADJACENT AREAS OF CANADA. AT THE SURFACE...A COLD
FRONT IS ADVANCING SLOWLY SOUTHWARD ACROSS THE MID MISSISSIPPI
VALLEY TOWARDS THE SOUTHEAST.

SIMILAR TO YESTERDAY...THE SCATTERED SHOWERS AND STORMS THAT HAVE
DEVELOPED DURING THE PEAK HEATING OF THE DAY SHOULD GREATLY DIMINISH
IN COVERAGE A COUPLE HOURS AFTER SUNSET TONIGHT. BUT WITH THE COLD
FRONT ADVANCING TOWARDS THE AREA...PRECIP CHANCES WILL INCREASE
AGAIN OVERNIGHT NORTH AS THE FRONT PROVIDES A SOURCE OF LOW LEVEL
LIFT. DID NOT GO HIGHER THAN CHANCE POPS...HOWEVER...AS THE 1 AM TO
7 AM TIME FRAME WILL HAVE A MINIMUM OF INSTABILITY TO SUPPORT
THUNDERSTORMS. IT IS WORTH NOTING THE THE LATEST RUNS OF THE RAP
REDEVELOP STORMS LATE OVERNIGHT ACROSS OUR NORTHERN COUNTIES AHEAD
OF THE FRONT. OVERNIGHT LOWS WILL BE AROUND NORMAL FOR THIS TIME OF
YEAR...IN THE LOW TO MID 70S.

FOR THURSDAY CONTINUED THE LIKELY POPS OF AROUND 60% FOR THE ENTIRE
CWA WITH THE COLD FRONT IMPINGING ON THE REGION. WIND SHEAR REMAINS
TOO LOW TO SUPPORT ORGANIZED SEVERE CONVECTION...BUT A COUPLE OF
STRONG STORMS AHEAD OF THE FRONT THURSDAY AFTERNOON ARE NOT OUT OF
THE QUESTION AS INSTABILITY WILL BE MAXIMIZED DURING THAT TIME. BY
THURSDAY EVENING THE INITIAL WIND SHIFT ASSOCIATED WITH THE FRONT
WILL PROBABLY BE STALLED ACROSS THE SOUTHERN PORTIONS OF ALABAMA...
BUT THE SURFACE DEW POINT DECREASE LOOKS TO LAG BEHIND THE INITIAL
WIND SHIFT. FOR THIS REASON...KEPT THE SLIGHT CHANCE TO LOW CHANCE
POPS FOR ROUGHLY THE SOUTHEASTERN HALF OF OUR CWA THURSDAY NIGHT...
MAINLY BEFORE 1 AM. WITH THE HIGHER PRECIP COVERAGE EXPECTED
TOMORROW...WENT A COUPLE DEGREES COOLER FOR HIGHS COMPARED TO
TODAY. AS IS TYPICAL IN THE SUMMER WITH A LONGWAVE UPPER TROUGH
WELL TO OUR NORTH...THE SURFACE FRONT WILL LIKELY STALL NEAR THE
GULF COAST OR SLIGHTLY INLAND. WILL MAINTAIN LOW POPS IN THE
SOUTHERN THIRD OF OUR AREA FOR FRIDAY TO ACCOUNT FOR THIS.

IT LOOKS LIKE WE MAY GET A BREAK FROM THE RAIN CHANCES ON SATURDAY
AS THE UPPER RIDGE TO OUR WEST NUDGES SLIGHTLY EASTWARD. THIS WILL
BRING SLIGHTLY HIGHER HEIGHTS OVER CENTRAL ALABAMA...REDUCING RAIN
CHANCES TO LESS THAN 20% FOR ALMOST THE WHOLE AREA. HIGHS THIS
WEEKEND WILL BE A BIT WARMER THOUGH...GENERALLY IN THE LOW TO MID
90S. PRECIP CHANCES MAY RETURN ON SUNDAY AS A SHORTWAVE TROUGH DIGS
SOUTHEASTWARD FROM THE DAKOTAS TOWARDS THE GREAT LAKES...WHICH WILL
REESTABLISH THE LONGWAVE UPPER TROUGH ACROSS THE EASTERN CONUS AND
RESULT IN THE UPPER RIDGE SHIFTING BACK TO THE WEST. A SURFACE LOW
AHEAD OF THIS SHORTWAVE TROUGH WILL CROSS OVER THE NORTHERN TIER OF
THE UNITED STATES...AND YET ANOTHER STRONG TRAILING COLD FRONT WILL
APPROACH THE SOUTHEAST BY MONDAY. BOTH THE GFS AND ECMWF ARE IN GOOD
AGREEMENT ON THE TIMING OF THIS COLD FRONT...SO HAVE THE HIGHEST
POPS IN THE SUNDAY NIGHT AND MONDAY PERIODS AS THE FRONT IS FORECAST
TO MOVE THROUGH.

IF THIS SECOND FRONT SLOWS DOWN JUST SLIGHTLY...THEN IT WOULD MOVE
OVER CENTRAL ALABAMA MAINLY DURING THE DAY ON MONDAY...GIVING THE
ATMOSPHERE THE OPPORTUNITY TO DESTABILIZE AND STRONGER WINDS ALOFT
TO SPREAD OVER THE AREA. RIGHT NOW THE 35+ KT WINDS AT 6 KM LAG THE
FRONT BY SEVERAL HUNDRED MILES IN BOTH THE GFS AND ECMWF. BUT BOTH
MODELS ARE ALSO SUGGESTING THAT SOME LOW LEVEL MOISTURE POOLING
WILL BE POSSIBLE AHEAD OF THE FRONT...WHICH COULD RESULT IN STRONG
INSTABILITY VALUES...ESPECIALLY FOR THE SOUTHERN HALF OF OUR AREA.
NOT CONVINCED THE NECESSARY WIND SHEAR WILL BE IN PLACE FOR
ORGANIZED SEVERE WEATHER WITH THE FRONTAL PASSAGE AT THIS TIME...
BUT IT IS SOMETHING WE WILL BE WATCHING OVER THE NEXT FEW DAYS.

WITH THIS SECOND FRONT HAVING A DEEPER UPPER TROUGH SUPPORTING IT...
DO NOT THINK IT WILL HAVE ANY TROUBLE CLEARING THE STATE. THIS WILL
BRING AN END TO THE RAIN CHANCES BY TUESDAY...AND BELOW NORMAL
TEMPERATURES BEGINNING MONDAY NIGHT ACROSS THE NORTH AND FOR ALL OF
CENTRAL ALABAMA TUESDAY THROUGH WEDNESDAY NIGHT. CONTINUED THE TREND
OF GREATLY UNDERCUTTING THE EXTENDED MOS GUIDANCE (MEX) TEMPERATURES
NEXT TUESDAY AND WEDNESDAY.

77/GLEASON

&&

.AVIATION...
18Z TAF DISCUSSION.

SCATTERED SHOWERS/STORMS ALREADY ONGOING ACROSS NORTH CENTRAL
ALABAMA AT THIS HOUR...AND COVERAGE SHOULD INCREASE OVER THE NEXT
FEW HOURS. NORTHERN TERMINALS HAVE BEST RAIN CHANCES AND HAVE
ADDED SHRA TO THE VCTS AT TCL/BHM/EET/ANB. HAVE MAINTAINED VCTS IN
THE SOUTH AS RAIN CHANCES ARE SLIGHTLY LOWER IN THAT AREA. WILL
AMEND AS NECESSARY THRU THE AFTERNOON. COVERAGE SHOULD DECREASE
AFTER SUNSET...BUT LINGERING SHOWERS ARE POSSIBLE IN THE NORTH
OVERNIGHT AS A FRONTAL BOUNDARY SLIDES SOUTH INTO THE TENNESSEE
VALLEY.

FOR TONIGHT...NOT EXPECTING ANY WIDESPREAD LOW CIGS BUT PATCHY FOG
WILL BE POSSIBLE. HAVE GONE WITH PERSISTENCE AND HAVE MVFR VIS
MENTIONED AT TERMINALS THAT OBSERVED FOG LAST NIGHT.

19

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     71  85  67  88  68 /  50  60  20  10   0
ANNISTON    71  85  69  88  69 /  30  60  20  10   0
BIRMINGHAM  72  86  70  89  71 /  40  60  20  10   0
TUSCALOOSA  72  88  70  91  70 /  30  60  10  10   0
CALERA      72  87  71  89  71 /  30  60  20  10   0
AUBURN      70  87  70  87  71 /  20  60  40  20  10
MONTGOMERY  72  90  72  91  73 /  20  60  30  20  10
TROY        69  89  71  89  71 /  20  60  30  30  10

&&

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

&&

$$






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