Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 291157
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
657 AM CDT FRI APR 29 2016

.UPDATE...
FOR 12Z AVIATION...FORECAST UPDATE...AND DENSE FOG ADVISORY.

&&

.DISCUSSION...

DENSE FOG HAS DEVELOPED VERY QUICKLY ALONG THE U.S. 80/I-85
CORRIDOR THIS MORNING, AND NEAR ZERO VISIBILITIES ARE BEING
OBSERVED ON SKYCAMS AND TRAFFIC CAMS. THEREFORE, HAVE ISSUED A
DENSE FOG ADVISORY IN EFFECT THROUGH 9AM FOR SOUTHERN AND
SOUTHEASTERN CENTRAL ALABAMA COUNTIES.

OTHER FORECAST UPDATE FOR TODAY INCLUDED UPDATING POPS TO LIKELY
FOR WESTERN AND NORTHWEST COUNTIES LATE THIS AFTERNOON AND INTO
THE EARLY EVENING. BETTER AGREEMENT HAS EMERGED BETWEEN HIGH-
RESOLUTION GUIDANCE IN AN MCS PUSHING SOUTHEASTWARD INTO CENTRAL
ALABAMA. THE WRF-ARW AND HRRR NOW SHOW A PRONOUNCED LINE OF STRONG
STORMS MOVING INTO NORTHWESTERN CENTRAL ALABAMA COUNTIES BETWEEN
4PM AND 7PM, AND QUICKLY PUSHING TO THE I-65 AND I-20/59 CORRIDORS
AFTER 7PM. WE`LL HAVE TO MONITOR CONVECTIVE TRENDS CLOSELY
THROUGH THE DAY, AS WELL AS MONITOR THE POTENTIAL STRENGTH OF THE
LINE OF STORMS. AMPLE AMOUNTS OF SURFACE BASED INSTABILITY AND DRY
AIR ALOFT WILL AID IN THE DEVELOPMENT AND PROPAGATION OF THE MCS
THROUGH THE DAY. STAY TUNED FOR UPDATES THROUGH THE DAY.

56/GDG

&&

.AVIATION...
12Z TAF DISCUSSION.

DENSE FOG HAS DEVELOPED ACROSS SOUTHERN ALABAMA THIS MORNING AND
AFFECTING THE TERMINALS AT KMGM AND KTOI THIS MORNING. LIFR VIS
AND CIGS WILL CONTINUE THROUGH AT LEAST 14Z BEFORE MIXING WILL
ALLOW THE FOG TO DISSIPATE. SOUTHERN TERMINALS WILL IMPROVE TO VFR
BY THE MID MORNING HOURS. THE OTHER AVIATION CHALLENGE TODAY WILL
BE THE CHANCE OF SHOWERS AND STORMS PUSHING INTO NORTHERN ALABAMA
LATE THIS AFTERNOON AND EARLY EVENING. SHORT-RANGE GUIDANCE IS IN
AGREEMENT WITH A LINE OF STORMS PUSHING SOUTHWARD AND AFFECTING
MANY NORTHERN TERMINALS. FOR NOW, HAVE ADDED IN VCTS AT KTCL,
KEET, AND KBHM FOR THE POSSIBILITY, AND WE MAY NEED TO ADD IN A
PREVAILING TSRA GROUP IF CONFIDENCE INCREASES IN THE 18Z TAF
ISSUANCE.

56/GDG

&&

.FIRE WEATHER...

ISOLATED TO SCATTERED SHOWERS AND STORMS ARE POSSIBLE THE NEXT TWO
DAYS...BEFORE MORE WIDESPREAD RAINFALL IS EXPECTED SUNDAY. DEPENDING
ON HOW QUICKLY A FRONT CLEARS THE AREA...RAIN CHANCES COULD LINGER
INTO EARLY NEXT WEEK. NO FIRE WEATHER CONCERNS AT THIS TIME.

&&

.PREV DISCUSSION...
/ISSUED 417 AM CDT FRI APR 29 2016/
SHORT TERM...
TODAY THROUGH TONIGHT.

A FAIRLY QUIET OVERNIGHT PERIOD IS UPON CENTRAL ALABAMA. PATCHY
DENSE FOG HAS DEVELOPED OVER A FEW LOCATIONS, BUT WIDESPREAD FOG IS
NOT EXPECTED AT THIS TIME. RELATIVELY DRIER AIR IS IN PLACE THIS
MORNING, AS THE OLD SURFACE FRONT MOVED NEAR THE I-20 CORRIDOR
YESTERDAY AND HAS SINCE WASHED OUT. IN TERMS OF THE FORECAST TODAY,
IT WILL BE CHARACTERIZED AS ONE OF OUR FIRST "HOT" DAYS OF THE YEAR.
LOW LEVEL THICKNESSES SHOULD EASILY SUPPORT MID TO UPPER 80S WITH A
SURFACE RIDGE CENTERED OVER SOUTHERN GEORGIA. UPPER LEVEL RIDGING TO
OUR SOUTH WILL ALSO AMPLIFY. THE BIG QUESTION WILL BE IF WE WILL SEE
ANY WIDESPREAD SHOWER AND THUNDERSTORM DEVELOPMENT. THE NEGATIVELY
TILTED TROUGH CURRENTLY CENTERED OVER THE FOUR CORNERS STATES WILL
HELP TO TRIGGER WIDESPREAD STRONG TO SEVERE STORMS ACROSS THE
SOUTHERN PLAINS.

ADDITIONAL SHOWERS AND STORMS WILL BE FOCUSED ALONG A NORTHWARD
MOVING WARM FRONT ACROSS THE ARKLATEX. A COMPLEX OF SHOWERS AND
STORMS THAT`S ALREADY DEVELOPING ACROSS SOUTHWESTERN ARKANSAS IS
FORECAST TO EXPAND IN COVERAGE AND PUSH EASTWARD THROUGHOUT THE DAY.
HIGH-RES GUIDANCE IS ADVERTISING THAT AN MCS WILL PUSH ACROSS
NORTHERN MISSISSIPPI THIS AFTERNOON, AND POSSIBLY MOVE INTO
NORTHWEST ALABAMA LATE THIS AFTERNOON AND INTO THE EARLY EVENING
HOURS. OF COURSE THE MCS WOULD BE GREATLY WEAKENED BY THE TIME IT
REACHED ALABAMA, BUT WOULD CERTAINLY THROW A WRENCH INTO THE POP
FORECAST. FOR NOW, SINCE THE HIGH-RES GUIDANCE HAS CONTINUED TO GAIN
TRACTION ON THE MCS SOLUTION, HAVE INCREASED TO HIGH CHANCE POPS
ACROSS THE NORTHWEST COUNTIES LATE THIS AFTERNOON. THE EXTENT OF
CHANCE POPS THEN INCREASES SOUTH AND EASTWARD INTO THE EARLY EVENING
HOURS DUE TO THE CHANCE OF ANYTHING LEFT OVER FROM THE MCS PUSHING
TOWARD THE I-65 CORRIDOR. IT`S CERTAINLY NOT A HIGH CONFIDENCE
FORECAST, AND WILL INVOLVE WATCHING CONVECTIVE TRENDS THROUGH THE
DAY. OTHERWISE, AN ISOLATED SHOWER OR STORM CAN`T BE RULED OUT
ACROSS SOUTHWESTERN AND SOUTHERN COUNTIES DURING THE HEATING OF THE
DAY, WHERE THE GREATEST MOISTURE AXIS WILL EXIST.

ANY LEFTOVER DRY AIR ACROSS OUR EASTERN AND NORTHEASTERN COUNTIES
WILL BE ERODED OVERNIGHT TONIGHT, AS SOUTHERLY SURFACE FLOW TAKES
BACK OVER. AN ISOLATED SHOWER OR STORM CAN`T BE RULED OUT ACROSS OUR
NORTHWEST COUNTIES WHERE THE MOST UPPER LEVEL ENERGY WILL BE
PRESENT. ALSO, THE LOW LEVEL 925MB JET WILL BE STRONGEST OFF TO OUR
NORTHWEST. OTHERWISE, IT WILL BE DOWNRIGHT MUGGY OUTSIDE OVERNIGHT
TONIGHT AS DEWPOINTS INCREASE INTO THE MID TO UPPER 60S, ESPECIALLY
ACROSS THE SOUTHERN HALF OF THE STATE. COVERAGE OF SHOWERS AND
STORMS WILL BE ON THE INCREASE ACROSS THE NORTHERN AND NORTHWEST
COUNTIES THROUGH DAYBREAK ON SATURDAY.

56/GDG

LONG TERM...
SATURDAY THROUGH THURSDAY.

A CLOSED LOW WITHIN THE LONGWAVE TROUGH OVER MUCH OF THE WESTERN
CONUS WILL ROTATE OVER THE CENTRAL PLAINS SATURDAY TOWARD THE
MIDWEST. THIS WILL PUSH THE MID LEVEL RIDGE AXIS TO OUR EAST
LEAVING CENTRAL ALABAMA UNDER SOUTHWESTERLY FLOW. AN ENHANCED LLJ
LIFTS FROM OUR WEST TO NORTH DURING THE DAY...AND BETTER UPPER
LEVEL JET STRUCTURES ARE WELL TO OUR WEST. WITH A WARM FRONT TO
OUR NORTH...THE AREA WILL BE WARM AND UNSTABLE DURING THE
AFTERNOON...BUT WITHOUT AN ORGANIZED FORCING MECHANISM TO SPUR
CONVECTION FOR MUCH OF THE AREA. OUTSIDE OF THE NORTHWESTERN
COUNTIES...WHICH WILL BE CLOSER TO BETTER FORCING ASSOCIATED WITH
THE UPPER LOW...SCATTERED DIURNALLY DRIVEN ACTIVITY WILL BE
POSSIBLE. BELIEVE MOST OF THE AREA WILL BE DRY UNTIL SATURDAY
EVENING WHEN A STRONGER SHORTWAVE ROTATING THROUGH THE TROUGH
CROSSES THE AREA.

SATURDAY NIGHT...THE SURFACE LOW WILL BE TO OUR NORTHWEST MOVING
TOWARD THE OHIO RIVER VALLEY WITH A FRONT STRETCHING SOUTHWARD
ALONG THE MISSISSIPPI RIVER BY SUNRISE. SHOWERS AND THUNDERSTORMS
WILL INCREASE IN COVERAGE AS THE ABOVE MENTIONED SHORTWAVE
CROSSES THE AREA AND THE FRONT PUSHES EASTWARD. THIS TREND
CONTINUES SUNDAY DUE TO THE SLOW MOVING NATURE OF THE FRONT. AT
SOME POINT...EXPECT THE BETTER FORCING TO OUT PACE THE FRONT AND
RAIN COVERAGE WILL DECREASE ACROSS PORTIONS OF THE AREA. DIFFICULT
TO PINPOINT WHEN THAT WILL HAPPEN AT THIS POINT...AS MODEL
SOLUTIONS CONTINUE TO DIFFER ON THE PROGRESSION OF BOTH THE FRONT
AND UPPER LEVEL SUPPORT BEYOND EARLY SUNDAY. IF THE ECMWF
VERIFIES...THE FRONT WILL STALL...WAITING FOR THE NEXT SHORTWAVE
TO MOVE OUT OF THE PLAINS AND WIDESPREAD RAINFALL WILL CONTINUE
MONDAY AND TUESDAY.

THE SECOND HALF OF NEXT WEEK LOOKS DRIER...WITH NORTHWESTERLY FLOW
AND HIGH PRESSURE DOMINATING THE EASTERN CONUS FOR SEVERAL DAYS.

14

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     86  64  83  64  81 /  10  20  40  60  70
ANNISTON    86  63  83  65  81 /  10  20  30  50  70
BIRMINGHAM  87  66  83  67  80 /  40  60  30  50  70
TUSCALOOSA  87  68  84  67  82 /  60  60  20  50  70
CALERA      86  66  83  66  81 /  30  50  20  50  70
AUBURN      87  64  84  66  83 /  10  10  20  30  50
MONTGOMERY  89  66  86  68  85 /  20  20  20  30  50
TROY        89  65  87  67  85 /  20  20  20  20  40

&&

.BMX WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY UNTIL 9 AM CDT THIS MORNING FOR THE FOLLOWING
COUNTIES: AUTAUGA...BARBOUR...BULLOCK...CHAMBERS...DALLAS...
ELMORE...LEE...LOWNDES...MACON...MONTGOMERY...PIKE...RUSSELL...
TALLAPOOSA.

&&

$$



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