Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 220042 AAB
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
742 PM CDT TUE OCT 21 2014

.UPDATE...
EVENING UPDATE.

&&

.DISCUSSION...
A PLEASANT EVENING IS UNDERWAY ACROSS THE TENNESSEE VALLEY, WITH
EVENING TEMPERATURES ALREADY FALLING INTO THE MIDDLE 50S IN A FEW
LOCATIONS AS OF THIS WRITING. A REINFORCING COLD FRONT IS IN THE
PROCESS OF PUSHING SOUTHWARD THROUGH THE CWFA, WITH SLIGHTLY
COOLER/DRIER AIR IN TOW. THIS FRONT EXTENDS FROM CENTRAL IA/MO
SOUTHEASTWARD THROUGH SRN MIDDLE TN/NRN AL/GA AND THEN NORTHEASTWARD
INTO THE CAROLINAS/VIRGINIAS. NO PRECIPITATION IS OCCURRING WITH THIS
FRONT, AND IN FACT, ONLY A BRIEF WIND GUST OR TWO CAN BE PICKED OUT
ON REGIONAL METARS JUST TO OUR NORTH.

WEAK CAA OVERNIGHT IN ADDITION TO CLEAR SKIES/CALM WINDS WILL ALLOW
MORNING LOWS TO FALL INTO THE LOWER 40S, WITH A FEW NOTORIOUSLY
COOLER SPOTS DIPPING INTO THE UPPER 30S. WILL RETAIN THE FOG MENTION
FOR MAINLY SHELTERED VALLEY LOCATIONS, AS WELL AS THOSE IN CLOSE
PROXIMITY TO RIVERS/LAKES. ASIDE FROM A FEW ADJUSTMENTS TO HOURLY
TEMP GRIDS TO MATCH UP WITH OBSERVATIONAL TRENDS, NO ADDITIONAL
CHANGES WERE WARRANTED FOR THIS UPDATE.

FRESHENED WORDING IN AND HAVE ALREADY SENT UPDATED PRODUCTS.

12

&&

.AVIATION...
/ISSUED 613 PM CDT TUE OCT 21 2014/
FOR 00Z TAFS...
A DRY COLD FRONT WILL MOVE ACROSS THE TERMINALS THIS EVENING, WITH
N/NW WINDS EXPECTED AOB 5KTS OVERNIGHT. ASIDE FROM IFR FOG DEVELOPING
AGAIN AT KMSL BETWEEN 22/7-11Z, VFR CONDS WILL PREVAIL AT BOTH TAF
SITES THRU THE PERIOD, WITH N/NW WINDS ARND 10KTS EXPECTED TOMORROW.

12

&&

.PREV DISCUSSION...
/ISSUED 206 PM CDT TUE OCT 21 2014/
THE 18Z SURFACE ANALYSIS AND IR/VISIBLE SATELLITE IMAGES INDICATED
THAT A WEAK AND DIFFUSE COLD FRONT WAS MOVING SOUTHEAST THROUGH
KENTUCKY. THE FORECAST AREA WAS ALREADY IN A NORTHWEST FLOW IN THE
WAKE OF THE PREVIOUS COLD FRONT THAT MOVED THROUGH ON MONDAY. TEMPS
WERE IN THE UPPER 60S IN SOUTHERN MIDDLE TENNESSEE...AND INTO THE LOW
TO MID 70S ACROSS THE REST OF THE FORECAST AREA UNDER MOSTLY SUNNY
SKIES.

IN THE SHORT TERM...THE MODELS ARE IN GOOD AGREEMENT WITH MOVING THE
WEAK COLD FRONT SOUTHEAST THROUGH THE REGION BY THIS EVENING WITH
CLEAR SKIES EXPECTED. WINDS SHOULD BECOME LIGHT AFTER 06Z TONIGHT AND
WITH THE TEMP/DEWPOINT SPREAD EXPECTED TO AGAIN BE LESS THAN FIVE
DEGREES BY WEDNESDAY MORNING...WILL AGAIN MENTION VALLEY/RIVER FOG
FOR THE FORECAST AREA IN TONIGHTS FORECAST. THE SHORT TERM MODELS
INDICATE THAT THE SLOW MOVING EASTERN U.S. MID-UPPER TROUGH WILL
CONTINUE TO ALLOW A NORTH-NORTHEAST LOW-LEVEL WIND FLOW ACROSS THE
REGION THROUGH THURSDAY. THIS SHOULD RESULT IN CONTINUED SLIGHTLY
COOLER THAN NORMAL TEMPS. HAVE FOLLOWED CLOSELY TOWARD A MIX BETWEEN
GFS AND ECMWF TEMP GUIDANCE THROUGH THURSDAY.

BY LATE THURSDAY...THE GFS/ECMWF MODELS INDICATE THAT ANOTHER
WEAKENING COLD FRONTAL BOUNDARY WILL MOVE EAST-SOUTHEAST THROUGH THE
LOWER OHIO VALLEY WITH ANY MOISTURE EXPECTED TO REMAIN GENERALLY
NORTH OF TENNESSEE. THIS COLD FRONT SHOULD MOVE THROUGH THE FORECAST
AREA BETWEEN THE FRIDAY AFTERNOON/EVENING TIME FRAME WITH A QUICK
WIND SHIFT TO THE NORTHWEST EXPECTED. THE ECMWF AND GFS MODELS ARE
IN GOOD AGREEMENT INVOLVING BUILDING A LARGE MID TO UPPER LEVEL
RIDGE OF HIGH PRESSURE EASTWARD INTO THE TENNESSEE VALLEY BY
SATURDAY. THE BACK SIDE OF THE SURFACE RIDGE IS EXPECTED TO SLIDE
EAST OF THE AREA ON SUNDAY...WITH TEMPS EXPECTED TO WARM TO ABOVE
NORMAL LEVELS FOR THIS TIME OF THE YEAR.

THE GFS/ECMWF MODELS ARE IN FAIR AGREEMENT AT THE END OF THE
EXTENDED FORECAST PERIOD INVOLVING BREAKING DOWN THE UPPER
RIDGE. AN UPPER TROUGH IS PROGGED TO THEN DIG SOUTHEAST INTO THE
SOUTHERN PLAINS/OHIO VALLEY REGION BY TUESDAY. A SURFACE COLD FRONT
IS EXPECTED TO WEAKEN AS IT APPROACHES THE REGION LATE IN THE DAY ON
TUESDAY. HAVE NOT ADDED IN ANY MENTION OF SHOWERS/STORMS FOR TUESDAY
YET...AS THE TIMING IS NOT FOR CERTAIN YET AND THE TRACK RECORD OF
THE PREVIOUS FEW COLD FRONTS COULD MEAN THIS COLD FRONT MAY
DISSIPATE/WEAKEN ENOUGH TO BE A DRY BOUNDARY. HAVE UPPED TEMPS
SLIGHTLY IN THE EXTENDED FORECAST PERIODS TO ACCOUNT FOR MODEL RUN
CONSISTENCIES OVER THE PAST COUPLE OF DAYS.

TT

&&

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

$$

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



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