Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 201130 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
630 AM CDT MON OCT 20 2014

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 511 AM CDT MON OCT 20 2014/
SURFACE OBS AND SATELLITE DATA PROVIDED BY NASA SPORT CONFIRM THAT
AREAS OF DENSE VALLEY FOG HAVE DEVELOPED IN STRONG RADIATIONAL
COOLING REGIME AROUND THE LOCAL AREA. AT THIS TIME...AREAL COVERAGE
ONLY APPEARS TO WARRANT AN SPS...BUT WILL CONTINUE TO MONITOR IN THE
EVENT THAT AN ADVISORY BECOMES NECESSARY. OTHERWISE...WATER VAPOR
SATELLITE DATA INDICATES A MID-LEVEL SHORTWAVE TROUGH DIGGING
SOUTHEASTWARD ACROSS THE UPPER MISSISSIPPI VALLEY THIS MORNING...
WITH THIS FEATURE FORECAST TO REACH THE LOWER GREAT LAKES BY 12Z AND
GRADUALLY AMPLIFY LATER TODAY AS IT SHIFTS INTO THE EASTERN GREAT
LAKES. AS THE SOUTHERN END OF THIS WAVE PUSHES ACROSS THE REGION THIS
AFTERNOON/EVENING...A SUBTLE INCREASE IN MID-LEVEL FORCING FOR ASCENT
CAN BE EXPECTED. BASED ON TRENDS IN RADAR/SATELLITE DATA ACROSS THE
OZARKS/LOWER OHIO VALLEY...THIS FORCING WILL LIKELY BE SUFFICIENT TO
GENERATE A THICKENING DECK OF ALTOCUMULUS CLOUDS AND PERHAPS A
GENEROUS COVERAGE OF VIRGA SHOWERS. HOWEVER...LIMITED SUBCLOUD
MOISTURE EVIDENT IN FORECAST SOUNDINGS SUGGESTS LITTLE THREAT FOR
MEASURABLE PRECIP AND HAVE ONLY INCLUDED A 10 POP AT THIS TIME.
ISOLATED LIGHT SHOWERS WILL BE MENTIONED FOR OUR SOUTHERN
TENNESSEE/NORTHEAST ALABAMA COUNTIES AS SLIGHTLY STRONGER VERTICAL
MOTIONS IN THESE AREAS MAY RESULT IN A FEW DROPS OF RAIN.

STRONG NORTHWEST FLOW ALOFT WILL BECOME ESTABLISHED LATE TONIGHT AS
THE INITIAL SHORTWAVE TROUGH LIFTS NORTHEASTWARD TO THE NORTHERN
MID-ATLANTIC COAST...AND A STRONGER UPSTREAM WAVE TRACKING ACROSS
THE GREAT LAKES BEGINS TO CUTOFF IN THE SOUTHERN PORTION OF THE
LONGWAVE TROUGH AXIS. A THICKER DECK OF STRATUS CLOUDS WILL LIKELY
INVADE THE REGION OVERNIGHT IN ADVANCE OF A REINFORCING COLD FRONT
WHICH WILL LIKELY PUSH SOUTHWARD ACROSS THE REGION LATE TUESDAY
MORNING/EARLY TUESDAY AFTERNOON WITH LITTLE CHANGE IN SENSIBLE
WEATHER ASIDE FROM AN INCREASE IN NORTHWEST WINDS. SHORT TERM MODELS
SUGGEST THAT THE CUTOFF UPPER LOW WILL DRIFT GENERALLY SOUTHEASTWARD
AND OFFSHORE THE MID-ATLANTIC COAST BY THE END OF THE SHORT TERM
PERIOD...WITH STRONG NORTHWEST FLOW REMAINING IN PLACE TO THE EAST OF
AN AMPLIFIED MID-TROPOSPHERIC RIDGE APPROACHING FROM THE CENTRAL
PLAINS. WITH CENTER OF CANADIAN SURFACE RIDGE SINKING INTO THE GREAT
LAKES...A LIGHT NORTHEAST WIND WILL CONTINUE TO ADVECT COOLER/DRIER
AIR INTO THE REGION WITH LOWS WEDNESDAY MORNING IN THE LOWER/MID 40S
AND HIGHS WEDNESDAY ONLY REACHING THE MID/UPPER 60S.

THE MID-LEVEL RIDGE AXIS IS FORECAST TO TRANSLATE ACROSS THE REGION
WEDNESDAY NIGHT...WITH FLOW ALOFT BACKING TO THE WEST-SOUTHWEST
DURING THE DAY ON THURSDAY AS ANOTHER MID-LEVEL TROUGH SPREADS
EASTWARD ACROSS THE NORTHERN/CENTRAL PLAINS. ASSUMING HIGH-LEVEL
CLOUDS DO NOT INCREASE TOO EARLY IN THE PERIOD...WEDNESDAY
NIGHT/THURSDAY MORNING WILL BE ANOTHER STRONG RADIATIONAL COOLING
EVENT AS CENTER OF RIDGE MAY BE SUFFICIENTLY CLOSE TO ALLOW FOR
BOUNDARY LAYER DECOUPLING. IF THIS SCENARIO UNFOLDS...AREAS OF DENSE
VALLEY FOG WILL DEVELOP ONCE AGAIN FOR THE MAJORITY OF THE AREA...
WITH PATCHY FROST ALSO POSSIBLE IN SHELTERED VALLEYS OF SOUTHERN
MIDDLE TENNESSEE/FAR NORTHEAST ALABAMA. AFTER SEVERAL CONSECUTIVE
MODEL CYCLES SHOWING A LARGE CUTOFF LOW MOVING INTO THE NORTHERN GULF
THIS WEEKEND...THE GFS/ECMWF HAVE NOW COME INTO BETTER AGREEMENT ON A
MORE PROGRESSIVE SOLUTION SHOWING A QUICK PASSAGE OF THE NEXT TROUGH
AXIS FROM THURSDAY NIGHT-FRIDAY NIGHT. ONCE AGAIN...LIFT WILL BE
STRONG BUT MOISTURE WILL BE LACKING SO WILL ONLY INCLUDE A SILENT 10
POP AND INCREASE IN CLOUD COVER AT THIS POINT. A MODEST WARMING TREND
WILL DEVELOP BY EARLY NEXT WEEK AS THE SUBTROPICAL RIDGE BUILDS
EASTWARD INTO THE SOUTHERN U.S.

70/DD

&&

.AVIATION...
FOR 12Z TAFS...IFR CONDS WILL LINGER AROUND THE KMSL TERMINAL THROUGH
14Z...BEFORE EARLY MORNING BR/FG BEGINS TO DIMINISH. VFR CONDS ARE
OTHERWISE GENERALLY XPCTED THROUGH THE PERIOD. SCT/BKN MID/HIGH
CLOUDS ASSOCIATED WITH AN ONCOMING COLD FRONT OUT OF THE NW WILL
BEGIN TO STREAM ACROSS THE AREA LATER TODAY...BEFORE THINNING THIS
EVENING AS THE FRONT BEGINS TO MOVE SE OF THE AREA.

09

&&

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

$$

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



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