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Area Forecast Discussion

812
FXUS64 KHUN 190238 AAB
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
938 PM CDT FRI APR 18 2014

.UPDATE...TO LOWER TEMPERATURES AND EXTEND POPS PAST MIDNIGHT.

&&

.DISCUSSION...
SURFACE LOW PRESSURE SOUTHEAST OF APPALACHICOLA FLORIDA IS VERY
SLOWLY PUSHING EAST THIS EVENING. A LARGE CANOPY OF MID TO HIGH
CLOUDS REMAIN IN PLACE ACROSS NORTHERN ALABAMA AND SOUTHERN MIDDLE
TENNESSEE. AN UPPER LEVEL LOW CAN BEEN SEEN IN WATER VAPOR SWINGING
EAST TOWARD THE SURFACE LOW OFF THE FLORIDA COAST.

00Z GUIDANCE MOVES THE SURFACE LOW LITTLE UNTIL THE UPPER LOW CATCHES
UP AND THEN PHASES WITH IT TOWARD DAYBREAK. AS THESE PHASE A FEW
SHOWERS COULD DEVELOP IN OUR FAR SOUTHEASTERN COUNTIES OF DEKALB OR
MARSHALL THROUGH DAYBREAK. VERY LITTLE ACCUMULATION IS EXPECTED...BUT
CANNOT RULE OUT A QUICK FEW HUNDRETHS IN THE SOUTHERN PORTIONS OF
THESE COUNTIES. THEREFORE LEFT SLIGHT CHANCE OF RAIN IN FOR THESE
COUNTIES THROUGH 7 AM. CLOUD COVER SHOULD DIMINISH AFTER
MIDNIGHT...ESPECIALLY WEST OF I-65. THIS IS SUPPORTED BY CURRENT
SATELLITE TRENDS. THE PHASING OF THE UPPER LOW SHOULD REDEVELOP CLOUD
COVER EAST OF I-65 AROUND MIDNIGHT...BEFORE PARTLY CLOUDY SKIES WILL
PUSH EAST AFTER 3 OR 4 AM IN ALL COUNTIES EXCEPT MARSHALL AND DEKALB
COUNTIES. IN THOSE TWO COUNTIES EXPECT MOSTLY CLOUDY CONDITIONS TO
HOLD ON ALL NIGHT.

ADVECTION AROUND THE PHASING SURFACE AREA OF LOW PRESSURE WILL BRING
LOWER SURFACE DEWPOINTS INTO NORTHERN ALABAMA AND ESPECIALLY
SOUTHERN MIDDLE TENNESSEE. BASED ON UPSTREAM DEWPOINTS BETWEEN 39 AND
46 DEGREES...BELIEVE SOUTHERN MIDDLE TN COUNTIES AND COUNTIES
NORTH OF THE TN RIVER /THE EXCEPTION BEING DEKALB COUNTY/ COULD SEE
DEWPOINTS DROP TO BETWEEN 40 AND 45 DEGREES. WITH LIGHT WINDS AND
PARTLY CLOUDY CONDITIONS EXPECTED TO BE PREVALENT AFTER MIDNIGHT IN
THESE AREAS...LOW TEMPERATURES COULD DROP INTO THE LOWER 40S IN
SOUTHERN MIDDLE TN AND LOCATIONS NORTH OF THE TN RIVER IN
NORTHEASTERN ALABAMA. LOWERED TEMPERATURES TO REFLECT THIS. IN
MARSHALL AND DEKALB COUNTIES...WINDS AND CLOUD COVER SHOULD KEEP LOWS
IN THE MID TO UPPER 40S. AS THE SURFACE LOW BEGINS TO PHASE TOWARD
DAYBREAK...WINDS SHOULD INCREASE TO BETWEEN 5 AND 10 MPH.

KTW

&&

.AVIATION...
/ISSUED 643 PM CDT FRI APR 18 2014/
FOR 00Z TAFS...
VFR CONDITIONS ARE EXPECTED THROUGH THE ENTIRE TAF PEROD. OVERCAST MID
TO HIGH LEVEL CLOUDS WILL SCATTER JUST AFTER MIDNIGHT. 10 TO 15 MPH
WINDS FROM THE NORTHEAST WITH GUSTS UP AROUND 20 KTS WILL DEVELOP
AFTER 19/13Z OR 19/14Z.

KTW

&&

.PREV DISCUSSION...
/ISSUED 226 PM CDT FRI APR 18 2014/
THE 19Z SURFACE OBS...AREA 88-DS AND IR SATELLITE IMAGERY INDICATED
THAT THE LARGE AREA OF SHOWERS WITH SOME MODERATE RAIN...WAS MOVING
MAINLY NORTH-NORTHEAST OUT OF CENTRAL ALABAMA INTO MAINLY NORTH
GEORGIA. SKIES WERE GENERALLY CLOUDY ACROSS NORTH ALABAMA AND INTO
SOUTHERN MIDDLE TENNESSEE. QUITE A BIT OF MID AND HIGH CLOUDS WERE
MOVING NORTH INTO THE FORECAST AREA AROUND THE PERIPHERY OF THE AREA
OF LOW PRESSURE ACROSS SOUTH ALABAMA. TEMPS WERE IN THE UPPER 50S TO
LOWER 60S ACROSS THE AREA.

WILL CONTINUE WITH A SLIGHT CHANCE/CHANCE OF SHOWERS MAINLY EAST OF
INTERSTATE 65 THROUGH THE EVENING DUE TO THE CLOSE PROXIMITY OF THE
AREA OF SHOWERS TO THE FORECAST AREA. IT WILL BE A TRICKY FORECAST
OVERNIGHT INVOLVING WHEN THE CLOUDS AND SYSTEM MOVE EAST-NORTHEAST OF
THE FORECAST AREA. FOR NOW...WILL CONTINUE WITH THE TRENDING THAT WE
HAVE GOING IN THE CURRENT FORECAST...BASED ALSO UPON SHORT TERM MODEL
TRENDS. WILL GO WITH CLEARING BY OR SHORTLY AFTER 06Z FROM THE WEST
TO THE EAST ACROSS THE FORECAST AREA. THE MODELS ARE SIMILAR IN
MOVING THE SURFACE LOW TO THE SOUTHEAST GEORGIA COAST BY 00Z SUNDAY.
SINCE NORTHEAST ALABAMA WILL BE CLOSER TO THE WESTERN PERIPHERY OF
THE CLOUD SHIELD ON SATURDAY...THERE MAY BE MORE OF PARTLY CLOUDY
CONDITIONS THERE...WITH MOSTLY SUNNY SKIES EXPECTED ELSEWHERE ACROSS
THE FORECAST AREA. TEMPS WILL BE MORE IN LINE WITH GFS GUIDANCE ON
SATURDAY.

AS WE HEAD INTO EASTER...WEAK HIGH PRESSURE WILL BE IN CONTROL OF THE
WEATHER ACROSS THE TENNESSEE VALLEY REGION. TEMPS WILL FOR A CHANGE
BE SLIGHTLY ABOVE NORMAL ON SUNDAY AND GENERALLY ACCEPT THE MORE
OPTIMISTIC CLOUD AND TEMP FORECASTS FROM THE GFS AND ECMWF MODELS.
THE NEXT STORM SYSTEM THAT WILL AFFECT THE FORECAST AREA BY LATE
MONDAY WILL TAKE SHAPE IN THE CENTRAL PLAINS STATES ON SUNDAY. WILL
CONTINUE WITH MONDAY AFTERNOON TSRA CHANCES FOR THE FORECAST AREA
AND WILL KEEP IN CHANCE POPS FOR MONDAY NIGHT AND INTO TUESDAY. THE
MODELS ARE IN GOOD AGREEMENT INVOLVING MOVING THE SURFACE COLD FRONT
THROUGH THE FORECAST AREA BY 18Z TUESDAY...WITH IMPROVING WEATHER
CONDITIONS EXPECTED BY THE AFTERNOON FROM THE WEST TO THE EAST ACROSS
THE FORECAST AREA. A LARGE AREA OF HIGH PRESSURE WILL THEN BUILD INTO
THE LOWER OHIO AND TENNESSEE VALLEYS BY LATER TUESDAY AND WILL SHIFT
EASTWARD THROUGH THE REGION THROUGH THURSDAY. WITH MORE OF A ZONAL
MID TO UPPER FLOW IN PLACE...TEMPS WILL REMAIN SLIGHTLY ABOVE NORMAL
AND SHOULD BE NICE FOR THIS TIME OF THE YEAR THROUGH THURSDAY.

ANOTHER COLD FRONT IS PROGGED BY THE GFS AND ECMWF MODELS TO SHIFT
SOUTHEAST THROUGH THE CENTRAL PLAINS AND INTO THE LOWER OHIO VALLEY
BETWEEN THURSDAY AND FRIDAY. THE GFS IS SLOWER WITH THE SOUTHEAST
MOVEMENT OF THE COLD FRONT...KEEPING IT NORTHWEST OF THE FORECAST
AREA THROUGH FRIDAY AFTERNOON. THE ECMWF MODEL IS MORE PROGRESSIVE
WITH THIS SYSTEM...WITH PRECIP PROGGED TO MAKE IT INTO THE AREA BY
FRIDAY AFTERNOON. DUE TO THE LACK OF MODEL CONSISTENCY...WILL NOT
INTRODUCE SHRA/TSRA CHANCES FOR FRIDAY YET. WILL KEEP TEMPS NEAR
GUIDANCE THROUGH THE END OF THE EXTENDED FORECAST PERIODS.

TT

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE
AT WEATHER.GOV/HUNTSVILLE.



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