Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 252335
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
535 PM CST WED FEB 25 2015

.UPDATE...
FOR 00Z AVIATION.

&&

.DISCUSSION...

FROM FAYETTE COUNTY EASTWARD ACROSS NORTHERN JEFFERSON TO CALHOUN
COUNTY...A BATTLE IS BEING WAGED BETWEEN WARM ADVECTION AND
DIABATIC COOLING FROM MELTING SNOW. THIS TRANSITION ZONE IS
DEPICTED CLEARLY IN DUAL-POL DATA...AND HAS PAUSED AFTER MOVING
SOUTHWARD RATHER QUICKLY OVER THE PAST FEW HOURS. OUR 21Z SOUNDING
SHOWS TEMPERATURES AS WARM AS 4C AROUND 850MB...SO THERE IS QUITE
A TEMPERATURE GRADIENT BETWEEN KBMX AND NORTHERN JEFFERSON COUNTY.
HEAVY PRECIPITATION HAS BECOME A LITTLE MORE SPOTTY OVER THE LAST
HOUR...AND THE TRANSITION LINE APPEARS TO BE NUDGING NORTHWARD.
EVENTUALLY ADDITIONAL HEAVY PRECIP SHOULD BRING THIS LINE BACK
SOUTHWARD TOWARD THE I-20 CORRIDOR AS THE 850MB TROUGH PASSES
THROUGH LATE THIS AFTERNOON. HOWEVER...THE WINDOW FOR ACCUMULATION
ALONG THE I-20 CORRIDOR WILL BE CLOSING AS THE BACK EDGE OF THE
PRECIP SHIELD MOVES IN FROM MISSISSIPPI.

THUNDERSNOW WITH VERY HIGH SNOWFALL RATES HAS BEEN REPORTED IN
SEVERAL LOCATIONS. ACCUMULATIONS ACROSS THE NORTH COULD REACH 8
INCHES IN ISOLATED SPOTS. AS THE PRECIP MOVES OUT...TEMPERATURES
WILL DROP BELOW FREEZING OVERNIGHT ACROSS MUCH OF THE AREA...
ESPECIALLY IN AREAS THAT HAVE SUBSTANTIAL SNOWPACK.

87/GRANTHAM

THURSDAY THROUGH MONDAY...

ANOTHER SHORTWAVE WILL BE SLIDING THROUGH ON THURSDAY/THURSDAY
NIGHT ON THE BACK EDGE OF THE LONGWAVE TROUGH ACROSS THE EAST.
MODELS ARE HINTING AT SOME ISOLATED AREAS OF PRECIP...BUT THE MEAN
LAYER HUMIDITY SEEMS RELATIVELY TOO DRY TO SEE ANY ACCUMULATION
WITH THIS ROUND THURSDAY AFTERNOON. MAIN IMPACT HERE SHOULD BE
CLOUDS ONLY...POSSIBLY FLURRIES...BUT NOT ENOUGH TO MENTION.

ON SATURDAY...THE RIDGE SHIFTS FURTHER ACROSS THE U.S. TO THE EAST
OVER OHIO DURING THE DAY AND TO THE ATLANTIC COAST BY SATURDAY
NIGHT. THIS WILL CUT OFF OUR NORTHERLY FLOW AND BRING SOME RETURN
FLOW. ONLY LOW RAIN CHANCES RETURN BY SATURDAY AFTERNOON AND NIGHT
THOUGH AS OVERALL MOISTURE WILL BE LIMITED INITIALLY. THE NEXT
STORM SYSTEM WILL BEGIN TO SLIDE IN SUNDAY AND MAY PERSIST THROUGH
EARLY NEXT WEEK. WILL NEED TO MONITOR THE TRENDS ON THIS SYSTEM
FOR TUESDAY AS A STRONG COLD FRONT MOVES THROUGH AND COULD SEE A
RETURN OF STRONG TO EVEN SEVERE THUNDERSTORMS BY THE END OF THE
PERIOD. MUCH MORE ON THAT AS WE GET CLOSER.

16


&&

.AVIATION...
00Z TAF DISCUSSION.

IFR CONDITIONS CURRENTLY ACROSS THE TERMINALS. KBHM HAS REPORTED
A WINTRY MIX BUT FOR THE MOST PART LIQUID PRECIPITATION HAS BEEN THE
PREDOMINANT AT THE TERMINALS. EXPECT A WINTRY MIX OF RAIN SNOW
WILL BE POSSIBLE ACROSS THE NORTHERN TERMINALS THROUGH 03Z AND
SHOULD BEGIN TO SWITCH TO PREDOMINANT SNOW AROUND 03Z AND LAST
UNTIL ROUGHLY 06Z ACROSS THE NORTHERN TERMINALS. THERE IS A SHARP
GRADIENT IN SNOWFALL AMOUNTS AND EXPECT THIS WILL SET UP JUST TO
THE NORTH OF THE TERMINALS. THEREFORE...PRECIPITATION TYPE AT THE
TERMINALS IS HIGHLY UNCERTAIN.

05/MA

&&

.BMX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING UNTIL MIDNIGHT CST TONIGHT FOR THE
FOLLOWING COUNTIES: BLOUNT...CALHOUN...CHEROKEE...CLEBURNE...
ETOWAH...FAYETTE...JEFFERSON...LAMAR...MARION...PICKENS...ST.
CLAIR...TUSCALOOSA...WALKER...WINSTON.

WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR THE
FOLLOWING COUNTIES: BIBB...CLAY...RANDOLPH...SHELBY...TALLADEGA.

WINTER WEATHER ADVISORY UNTIL 9 PM CST THIS EVENING FOR THE
FOLLOWING COUNTIES: GREENE...HALE...SUMTER.

&&

$$






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