Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 201142 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
642 AM CDT SAT SEP 20 2014

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 457 AM CDT SAT SEP 20 2014/
QUIET BUT SEASONABLY WARM/HUMID CONDITIONS PREVAIL ACROSS THE CENTRAL
TENNESSEE VALLEY THIS MORNING...WITH JUST A FEW PATCHES OF MID-
LEVEL CLOUDS MOVING SOUTHWARD IN THE NORTHERLY FLOW AROUND A
DEVELOPING MID-LEVEL CYCLONE ACROSS NORTH FLORIDA. OVERALL...VERY
LITTLE HAS CHANGED IN THE SHORT TERM PORTION OF THE FORECAST THIS
MORNING WITH A STRONG SHORTWAVE TROUGH -- CURRENTLY DIGGING
SOUTHEASTWARD ACROSS SASKATCHEWAN -- FORECAST TO REACH NORTH
DAKOTA/NORTHERN MINNESOTA BY THIS EVENING. THIS WILL FORCE THE NORTH
FLORIDA CLOSED LOW TO LIFT NORTHEASTWARD ALONG THE ATLANTIC COAST AND
ALLOW HEIGHTS TO GRADUALLY RISE ACROSS THE LOCAL AREA -- RESULTING IN
ANOTHER WARM AND GENERALLY DRY DAY. A REMOTE SHOWER/THUNDERSTORM MAY
DEVELOP THIS AFTERNOON ACROSS PORTIONS OF FAR NORTHWEST ALABAMA AS
WELL AS IN THE HIGHER TERRAIN OF SOUTHERN MIDDLE TENNESSEE...AS MID-
LEVEL SUBSIDENCE WILL BE A BIT WEAKER IN THESE REGIONS. HOWEVER...THE
THREAT IS TOO LOW TO INCLUDE ANYTHING OTHER THAN A 10 POP. HIGHS WILL
ONCE AGAIN RISE INTO THE MID/UPPER 80S...WITH SUFFICIENT DIURNAL
MIXING OF LOW-LEVEL MOISTURE ALLOWING LOWS TONIGHT TO BE JUST A
DEGREE OR SO COOLER THAN WHAT WE WILL EXPERIENCE THIS MORNING.

MOST MODELS AGREE THAT THE NORTHERN PLAINS VORT MAX WILL UNDERGO
FURTHER AMPLIFICATION AS IT SHIFTS EASTWARD ACROSS THE GREAT LAKES
TONIGHT AND INTO WESTERN NEW ENGLAND ON SUNDAY. A WEAK MID-LEVEL
SHEAR AXIS AND ASSOCIATED SURFACE TROUGH/WIND SHIFT LINE WILL LIKELY
MOVE SOUTHEASTWARD INTO THE REGION SUNDAY MORNING...PERHAPS
INITIATING THE DEVELOPMENT OF A FEW LATE MORNING SHOWERS. HOWEVER...
IT STILL APPEARS AS IF CONDITIONS WILL BE UNFAVORABLE FOR THE
DEVELOPMENT OF CONVECTION FOR MUCH OF SUNDAY AFTERNOON AS STRONG
SINKING MOTIONS TO THE SOUTH OF THE GREAT LAKES TROUGH OVERSPREAD THE
REGION FROM THE NORTH. THIS IS INDICATED WELL BY POINT FORECAST
SOUNDINGS WHICH ACTUALLY SUGGEST THAT CINH VALUES WILL INCREASE
THROUGH THE AFTERNOON. A GUSTY WESTERLY FLOW IN THE BOUNDARY LAYER
WILL PROMOTE STRONG WARMING ONCE AGAIN...WITH HIGHS PERHAPS A DEGREE
OR SO WARMER THAN TODAYS VALUES. THE THREAT FOR SHOWERS/THUNDERSTORMS
WILL INCREASE BY LATE AFTERNOON...AS A STRONG COLD FRONT PUSHES
SOUTHWARD -- EXTENDING FROM EASTERN KENTUCKY SOUTHWESTWARD TO WESTERN
TENNESSEE/CENTRAL ARKANSAS BY 00Z MONDAY. BASED ON EXPECTED TIMING OF
FRONTAL PASSAGE...WILL HAVE HIGHEST LATE AFTERNOON POPS ACROSS NW
ALABAMA/SRN TENNESSEE AND HIGHEST EARLY EVENING POPS ACROSS THE
REMAINDER OF THE FORECAST AREA. THE AREAL COVERAGE OF SHOWERS/STORMS
MAY ACTUALLY INCREASE AFTER 00Z AS GRADUAL HEIGHT FALLS ALOFT FORCE
THE CAP TO WEAKEN. COLD FRONT WILL LIKELY BE SOUTH OF THE ENTIRE
REGION BY 06Z MONDAY WITH A GUSTY NNE WIND ADVECTING COOLER/DRIER AIR
SOUTHWARD AS DEWPOINTS FALL INTO THE U40S/L50S BY MONDAY MORNING.
BEAUTIFUL AUTUMN WEATHER IS EXPECTED MONDAY...WITH ABUNDANT SUNSHINE
AND HIGHS ONLY REACHING THE MID/UPPER 70S FOR MOST LOCATIONS.

THESE CONDITIONS WILL PERSIST INTO THE BEGINNING OF THE EXTENDED
PERIOD...WITH COOL TEMPERATURES IN STORE ON MONDAY NIGHT/TUESDAY
MORNING. ALTHOUGH POSITION OF SURFACE RIDGE OVER THE UPPER OHIO
VALLEY WILL LIKELY MAINTAIN A LIGHT NORTHEAST FLOW OVER THE REGION
TEMPERATURES SHOULD STILL MANAGE TO FALL INTO THE UPPER 40S/LOWER
50S. FOR THE REMAINDER OF THE EXTENDED PERIOD...GLOBAL MODELS SUGGEST
THAT A MID-LEVEL RIDGE WILL BECOME ESTABLISHED OVER THE LOWER OHIO
VALLEY BY MID-WEEK...WITH ANOTHER INVERTED TROUGH EXPECTED TO DEVELOP
ACROSS THE SOUTHEASTERN ATLANTIC COAST. THIS TROUGH IS FORECAST TO
LIFT NORTHWESTWARD THROUGH THE END OF THE WEEK...AS THE MID-LEVEL
RIDGE AXIS BECOMES ESTABLISHED OVER THE GREAT LAKES DOWNSTREAM FROM A
MORE AMPLIFIED PACIFIC LONGWAVE TROUGH. EASTERLY FLOW WILL PERSIST AT
THE SURFACE...WITH A CONTINUATION OF DRY CONDITIONS AND A GRADUAL
WARMING TREND EXPECTED THROUGH NEXT WEEKEND.

70/DD

&&

.AVIATION...
FOR 12Z TAFS...VFR CONDITIONS ARE GENERALLY EXPECTED THRU 12Z/21. THE
MAIN EXCEPTION COULD BE RAPIDLY-DEVELOPING IFR-MVFR STRATUS PUSHING
NWWD FROM KATL AND KMGM. IT WOULD AFFECT KHSV BEFORE KMSL...AND
LIKELY WOULD BE LIFTING AND SCATTERING SOMEWHAT UPON ARRIVAL. HAVE
LIMITED ANY MENTION TO SCT015 THRU 14Z FOR NOW.

BCC

&&

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

$$

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


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