FXUS64 KBMX 111157
AFDBMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
555 AM CST FRI DEC 11 2009
.UPDATE...AVIATION DISCUSSION.
&&
.DISCUSSION...
ACTIVE SOUTHERN STREAM WILL BRING A SEVERAL DAY PERIOD OF
UNSETTLED CONDITIONS TO CENTRAL ALABAMA...BEGINNING TONIGHT AND
LASTING INTO TUESDAY. THERE ARE TWO MAIN WEATHER SYSTEMS TO DEAL
WITH DURING THIS TIME FRAME.
THE FIRST IS AN OVERRUNNING EVENT WHICH WILL BEGIN LATE TONIGHT.
MODELS HAVE BEEN FAIRLY CONSISTENT IN BRINGING AN AREA OF RAIN
NORTHWARD FROM THE GULF INTO CENTRAL ALABAMA AFTER MIDNIGHT
TONIGHT. MEANWHILE...THE BIG COLD SURFACE HIGH WILL SET UP SHOP
ALONG THE CAROLINA COAST. AS THE TOP DOWN MOISTENING PROCESS TAKES
PLACE...A COLD AIR DAMMING WEDGE WILL SET UP. THE SURFACE HIGH IS
NOT IN THE BEST POSITION...AND THIS CAD WEDGE WILL BE INDUCED AND
DRIVEN BY THE RAIN FALLING INTO AND EVAPORATING WITHIN THE DRY AIR
ASSOCIATED WITH THE HIGH. WHILE NOT A CLASSIC SETUP...THE MODELS
DEFINITELY HAVE THAT IN SITU CAD WEDGE "LOOK" TO THEM IN THE
SURFACE PRESSURE PATTERN.
SO...WHAT DOES IT ALL MEAN AS FAR AS OUR WEATHER GOES. WELL...IT
DOES LEND A BIT OF UNCERTAINTY TO THE LOW LEVEL TEMPERATURE AND
DEWPOINT PROFILE...AS THE MODELS TYPICALLY DON'T HANDLE THE
SHALLOW WEDGE AIR MASS VERY WELL. AND RIGHT NOW...I AM A BIT
FREAKED OUT BY THE SINGLE DIGIT AND BELOW ZERO DEWPOINTS NOT TOO
FAR TO OUR EAST THAT STAND TO GET ADVECTED INTO OUR AREA OVER THE
NEXT 24 HOURS. IF SOME OF THAT AIR CAN GET TRANSPORTED AND INTO
CENTRAL ALABAMA...AND GETS REPLENISHED AS THE OVERRUNNING RAINS
FALL INTO IT...THEN WE COULD SEE EVAPORATIONAL COOLING BEYOND THAT
CURRENTLY PREDICTED BY THE MODELS. THE MODELS ARE ALREADY PAINTING
A PICTURE THAT IS PERILOUSLY CLOSE TO FREEZING EARLY MONDAY
MORNING. WE WILL HAVE TO WATCH THE NEXT 12 TO 24 HOURS CAREFULLY.
HOPEFULLY...WE WON'T HAVE TO RAPIDLY RAMP UP A FREEZING RAIN
ADVISORY. AT THE WORST RIGHT NOW WE ARE JUST GOING TO GO WITH A
BRIEF PERIOD OF LIGHT SLEET AT THE ONSET OF PRECIPITATION...
TRANSITIONING TO A COLD RAIN FOR THE REST OF THE DAY ON MONDAY.
THE RAIN STICKS AROUND FOR UNTIL SUNDAY MORNING...WITH
TEMPERATURES NOT MOVING MUCH AT ALL UNTIL SUNDAY AFTERNOON. SUNDAY
NIGHT IS THE TRANSITION PERIOD...IN BETWEEN THE OVERRUNNING EVENT
AND THE COLD FRONT CONVECTIVE EVENT...WHICH COMES ON MONDAY AND
MONDAY NIGHT. CONDITIONS APPEAR TO WARM CONSIDERABLY AHEAD OF THE
COLD FRONT...AND THERE IS A BIT OF INSTABILITY ON THE MODEL PROGS
MONDAY AFTERNOON. THEREFORE...WILL CONTINUE TO INCLUDE THUNDER IN
THE FORECAST FOR MONDAY AND MONDAY NIGHT. THE LATEST MODEL RUNS
HAVE THE FRONT SURGING THROUGH HERE MONDAY NIGHT INTO TUESDAY...
WITH WHAT LOOKS LIKE AN AIR MASS THAT SHOULD AT LEAST BE AS COLD
AS THE ONE WE ARE CURRENTLY EXPERIENCING. THUS...I WENT A LITTLE
BELOW THE MEXMOS GUIDANCE IN THE TUESDAY THROUGH THURSDAY TIME
FRAME. NO PRECIPITATION IS INDICATED AFTER THE FRONT PUSHES TO THE
EAST OF US ON TUESDAY THROUGH THE REMAINDER OF THE 7 DAY FORECAST.
/61/
&&
.AVIATION...12Z TAF DISCUSSION.
VFR CONDITIONS ARE FORECAST FOR THE ENTIRE PERIOD. AN ACTIVE
SOUTHERN BRANCH JET STREAM WILL KEEP A STEADY STREAM OF MID AND HIGH
LEVEL CLOUDINESS OVER THE AREA. A FEW CEILINGS MAY APPROACH THE 8K
FT MARK FROM TIME TO TIME THROUGH 06Z...BUT THE PREDOMINANT HEIGHT
SHOULD BE ABOVE 10K FT. SURFACE WINDS WILL REMAIN RATHER LIGHT FROM
360 TO 030 WITH A GRADUAL SHIFT TOWARD THE EAST THROUGH THE PERIOD
AS THE SURFACE HIGH SHIFTS EASTWARD.
INCREASING MOISTURE WILL OCCUR TOWARD THE VERY END OF THE FORECAST
PERIOD. THERE IS A CHANCE OF SOME LIGHT RAIN...POSSIBLY MIXED WITH
SOME SLEET AT ONSET AT MGM/TOI. IF THE FROZEN PRECIP OCCURS...IT
WILL NOT AMOUNT TO MUCH. INCREASED RAIN CHANCES AND MVFR TO IFR
CEILINGS POSSIBLE RIGHT AT THE END OF THE PERIOD AND BEYOND.
75/LINHARES
&&
.FIRE WEATHER...
DEWPOINTS ARE LOW...AND AFTERNOON RELATIVE HUMIDITIES WILL DROP
INTO THE LOWER 20S FOR SEVERAL HOURS IN MOST LOCATIONS TODAY. WILL
UPGRADE THE FIRE WEATHER WATCH TO A RED FLAG WARNING FOR THIS
AFTERNOON.
&&
.PRELIMINARY POINT TEMPS/POPS...
GADSDEN 45 27 40 39 51 / 0 10 100 90 60
ANNISTON 47 31 40 40 53 / 10 10 100 90 70
BIRMINGHAM 48 32 42 42 58 / 10 20 100 90 60
TUSCALOOSA 48 34 44 43 60 / 10 30 90 90 40
CALERA 48 33 43 42 59 / 10 30 100 90 50
AUBURN 48 33 40 39 57 / 10 30 100 90 60
MONTGOMERY 48 34 44 44 62 / 10 50 100 90 50
TROY 48 35 44 43 64 / 10 60 100 90 60
&&
.BMX WATCHES/WARNINGS/ADVISORIES...
RED FLAG WARNING THIS AFTERNOON NORTH OF A DEMOPOLIS TO EUFAULA
LINE.
&&
$$
