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000
FXUS64 KHUN 041145 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
545 AM CST WED MAR 4 2015

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 424 AM CST WED MAR 4 2015/

THE PREVIOUSLY ADVERTISED WARM FRONT HAS NOW MOVED NORTH OF THE
FORECAST AREA...WITH MANY LOCATIONS IN THE MID TO UPPER 60S.
MEANWHILE...A COLD FRONT EXTENDS FROM UPSTATE NEW
YORK...SOUTHWESTWARD INTO EASTERN OKLAHOMA. SHOWERS...AND A FEW
THUNDERSTORMS...WERE OBSERVED JUST ALONG THIS FRONT...MOVING TO THE
NORTHWEST ACROSS WESTERN TENNESSEE. THIS FRONT WILL MAKE ITS SLOW
PROGRESSION SOUTHEAST TODAY...WITH MODEL CONSENSUS MOVING THE FRONT
INTO THE NORTHWESTERN PORTION OF ALABAMA BY 18Z...AND THEN SLOWLY
MOVING EAST OF THE AREA BETWEEN 00Z AND 03Z. PRIOR TO THE FRONT
REACHING THE FORECAST AREA...FORECAST HIGHS INTO THE UPPER 60S...AND
POSSIBLE LOWER 70S ARE EXPECTED. SHOWERS AND ISOLATED THUNDERSTORMS
WILL ALSO BE POSSIBLE ALONG THE FRONT.

AS THE FRONT MOVES EAST OVER THE NEXT 12 TO 18 HOURS...A SOUTHERN
STREAM CLOSED UPPER LEVEL LOW OVER SOUTHERN CALIFORNIA WILL PHASE
WITH A NORTHERN STREAM TROUGH. THE RESULTING LONGWAVE TROUGH WILL
SLOWLY PROGRESS EASTWARD...AS THE UPPER LEVEL JET STREAM
INTENSIFIES. THIS WILL PROVIDE AN ABUNDANCE OF LIFT BEHIND THE
FRONT...WITH WIDESPREAD SHOWERS EXPECTED TO DEVELOP BY THE EVENING.
MEANWHILE...THE SHALLOW COLD AIR BEHIND THE FRONT WILL MOVE IN FAIRLY
QUICKLY ACROSS THE FORECAST AREA...HOWEVER WITH TEMPERATURES RISING
TO NEAR 70 DEGREES PRIOR TO FRONTAL PASSAGE...IT WILL STILL BE AFTER
MIDNIGHT BEFORE TEMPERATURES FALL BELOW FREEZING. AS TEMPERATURES
FALL...RAIN WILL TRANSITION TO FREEZING RAIN FROM WEST TO EAST
THROUGH 12Z. MANY LOCATIONS ACROSS THE EAST MAY NOT SEE FROZEN PRECIP
UNTIL AFTER 12Z...HOWEVER HAVE KEPT A CHANCE FOR FREEZING RAIN MIXING
IN WITH RAIN...TO ACCOUNT FOR THE COLDER AIR POSSIBLY REACHING THESE
LOCATIONS SOONER THAN FORECAST. MODELS ARE COMING IN WITH BETTER
AGREEMENT THAT THE POST FRONTAL PRECIP WILL CONTINUE THROUGH AT LEAST
18Z...WITH MORE QPF THEN PREVIOUS RUNS. THEREFORE...INCREASED POPS
DURING THE 12Z TO 18Z TIME FRAME...WHICH PUTS THE EASTERN HALF OF THE
CWA IN FROZEN PRECIP LONGER. THEREFORE...ALSO MADE AN ADJUSTMENT TO
THE ICE ACCUMULATION GRIDS. CONFIDENCE IS A LITTLE ON THE LOW SIDE
CONCERNING THE SLEET AND SNOW MIXING IN WITH FREEZING RAIN. FORECAST
SOUNDINGS ACROSS THE BOARD SHOW THE WARM NOSE REMAINING IN PLACE
DURING THE HEAVIEST PRECIP...WITH THE TEMP PROFILE GOING BELOW
FREEZING JUST AS THE DRIER AIR FILTERS IN. HOWEVER KEPT THE CHANCE
FOR MODERATE SLEET ACROSS THE NORTHWESTERN PORTION OF THE AREA AND
LEFT THE SLEET/SNOW AMOUNTS UNCHANGED.

SLEET/SNOW ACCUMULATIONS OF UP TO AN INCH ARE POSSIBLE...MAINLY
ACROSS THE NORTHWESTERN 3 COUNTIES IN ALABAMA AND ALL OF SOUTHERN
MIDDLE TENNESSEE. ICE ACCUMULATIONS OF ONE TO THREE TENTHS OF AN
INCH WILL ALSO BE POSSIBLE. GIVEN THAT WE WILL BE FAIRLY WARM PRIOR
TO THE ONSET OF FROZEN PRECIP...MOST OF THE ACCUMULATIONS WILL BE ON
ELEVATED SURFACES. HOWEVER...THE MAJORITY OF THE FROZEN PRECIP IS
EXPECTED TO OCCUR JUST BEFORE...AND DURING...MORNING COMMUTE
TOMORROW...WHICH MAY CREATE HAZARDOUS TRAVEL CONDITIONS.
ADDITIONALLY...WINDS WILL BE IN THE 15 TO 20 KT RANGE WHILE PRECIP
IS FALLING...WHICH MAY LEAD TO GREATER ICE ACCUMULATIONS THAN
FORECAST. GIVEN THIS UNCERTAINTY...HAVE DECIDED TO INCLUDE
MADISON...MORGAN...AND CULLMAN COUNTIES TO THE WATCH...GIVEN THAT
QPF AMOUNTS MAY BE HIGHER THAN FORECAST IN THESE LOCATIONS AFTER
12Z.

PRECIP WILL TAPER OFF BY 18Z...WITH LINGERING LIGHT SNOW FLURRIES
POSSIBLE DURING THE AFTERNOON. TEMPERATURES WILL NOT WARM VERY MUCH
DURING THE DAY...AND MOST LOCATIONS WILL LIKELY STAY BELOW FREEZING.
TEMPS WILL BOTTOM OUT EARLY FRIDAY MORNING...WITH LOWS DROPPING INTO
THE TEENS. THIS...COMBINED WITH WINDS STAYING NEAR 10 KTS...WILL
CREATE FRIGID CONDITIONS ACROSS THE FORECAST AREA. THE GOOD NEWS IS
THAT THE FORECAST AREA WILL THEN EXPERIENCE A WARMING TREND DURING
THE EXTENDED PORTION OF THE FORECAST PERIOD. MODEL GUIDANCE BEYOND
FRIDAY IS INCONSISTENT...SO KEPT A BLEND OF THE GUIDANCE...WITH THE
CHANCE FOR LIGHT PRECIP RETURNING TO THE AREA ON MONDAY. TEMPS WILL
MODERATE TO NEAR NORMAL FOR THIS TIME OF YEAR.

73

&&

.AVIATION...
PERIODS OF SHOWERS ARE FORECAST TODAY. INCREASED INSTABILITY COULD
BRING AN ISOLATED T-STORM OR TWO...WITH THE PRIMARY THREAT FROM GUSTY
WINDS. MUCH COLDER TEMPS ARE EXPECTED THIS AFTERNOON AND EVENING...
AS AN ARCTIC COLD FRONT MOVES ACROSS THE REGION...AND TEMPS FALL
BELOW FREEZING AFTER MIDNIGHT WED NIGHT AND BEFORE DAYBREAK THU. THIS
WILL RESULT IN RAIN BECOMING A WINTRY MIX OF FREEZING RAIN AND SLEET.
SSW WINDS 10-20KT AT THE TAF START WILL BECOME WEST...THEN NNW AFTER
THE FRONT PASSES...WITH SOME GUSTS TO 25KT. LIGHTER WINDS AT THE
SURFACE THIS MORNING AND STRONGER WINDS ALOFT WILL BE CLOSE TO WIND
SHEAR CRITERIA.

RSB

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...WINTER STORM WATCH FROM LATE TONIGHT THROUGH THURSDAY AFTERNOON FOR
     ALZ001>007-016.

TN...WINTER STORM WATCH FROM LATE TONIGHT THROUGH THURSDAY AFTERNOON FOR
     TNZ076-096-097.

&&

$$

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AT WEATHER.GOV/HUNTSVILLE.