Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 191119 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
619 AM CDT FRI SEP 19 2014

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 517 AM CDT FRI SEP 19 2014/
WATER VAPOR SATELLITE IMAGERY CONFIRMS THAT THE LAST IN A SERIES OF
MID-LEVEL VORTICES CONTINUES TO APPROACH THE REGION FROM THE
NORTHWEST THIS MORNING. RADAR DATA INDICATES THAT REMNANTS OF EVENING
SHOWER ACTIVITY WHICH DEVELOPED YESTERDAY EVENING AS THIS SYSTEM
APPROACHED THE REGION CONTINUES TO DISSIPATE ACROSS CENTRAL
ALABAMA...WITH OBSERVATIONAL DATA SUGGESTING THAT THE SFC-850MB FRONT
REMAINS NEARLY STATIONARY -- BISECTING THE FORECAST AREA FROM NW-TO-
SE THIS MORNING. SHORT TERM MODELS AGREE THAT MID-LEVEL HEIGHTS WILL
RISE SLOWLY TODAY WITH WINDS ALOFT VEERING TO THE NORTH AS A TROUGH
AMPLIFIES ACROSS THE SOUTHEASTERN ATLANTIC COAST. ALTHOUGH STRONGEST
MID-LEVEL FORCING FOR ASCENT WILL BE SHIFTING SOUTHEASTWARD AWAY FROM
THE REGION THROUGH THE DAY...THE PREVIOUSLY MENTIONED FRONTAL ZONE
WILL LIFT NORTHWARD AND MAY PROVIDE SUFFICIENT LOW-LEVEL CONVERGENCE
FOR THE DEVELOPMENT OF ISOLATED/WIDELY SCATTERED CONVECTION FROM LATE
MORNING THROUGH THE AFTERNOON. CURRENT INDICATIONS ARE THAT COVERAGE
OF THIS ACTIVITY MAY BE A BIT HIGHER ACROSS THE SOUTHWEST HALF OF
THE AREA...WHERE INCREASING EAST-SOUTHEASTERLY FLOW WILL ADVECT MID
60 DEGREE DEWPOINTS NORTHWARD RESULTING IN HIGHER SB INSTABILITY. THE
EAST-SOUTHEASTERLY FLOW REGIME WILL PERSIST OVERNIGHT...PERHAPS
RESULTING IN A FAIR AMOUNT OF LOW STRATUS CLOUDS AND LIGHT FOG
SATURDAY MORNING WITH LOW TEMPERATURES MORE UNIFORM AND IN THE LOWER
60S FOR MOST LOCATIONS.

FROM TONIGHT THROUGH SATURDAY NIGHT...THE AMPLIFIED WAVE OVER THE
SOUTHEASTERN ATLANTIC COAST IS FORECAST TO INITIALLY CLOSE OFF
BEFORE SHEARING APART AND LIFTING RAPIDLY NORTH-NORTHEASTWARD JUST
OFF THE MID-ATLANTIC COAST. AS THIS OCCURS...A MID-LEVEL RIDGE
CURRENTLY ACROSS THE SOUTHERN PLAINS WILL BUILD EASTWARD IN ADVANCE
OF A STRONG VORT MAX PROGGED TO DIG SOUTHEASTWARD FROM THE SOUTHERN
CANADIAN PROVINCES INTO THE NORTHERN PLAINS BY SATURDAY EVENING. A
FEW SPRINKLES OF RAIN WILL BE POSSIBLE ACROSS NORTHWEST ALABAMA
TOMORROW IN THE LOW-LEVEL WARM ADVECTION REGIME...BUT OVERALL HEIGHT
RISES ALOFT WILL MAINTAIN DRY CONDITIONS AND SLIGHTLY WARMER
TEMPERATURES ON SATURDAY. DEPENDING ON THE AMOUNT OF LOW-LEVEL MIXING
THAT OCCURS ON SATURDAY AFTERNOON...LIGHT WINDS SATURDAY EVENING IN
PROXIMITY TO SURFACE RIDGE MAY ALLOW LOW TEMPERATURES SUNDAY MORNING
TO BE A FEW DEGREES COOLER. AS THE STRONG NORTHERN STREAM VORT MAX
BEGINS TO SHIFT EASTWARD OVER THE GREAT LAKES WITHIN BASE OF
AMPLIFYING LONGWAVE TROUGH...A STRONG COLD FRONT WILL PUSH
SOUTHWARD...EXTENDING FROM NORTHERN ARKANSAS INTO EASTERN KENTUCKY BY
SUNDAY EVENING. SCATTERED SHOWERS/THUNDERSTORMS WILL LIKELY DEVELOP
ALONG A PREFRONTAL WIND SHIFT AXIS ACROSS WESTERN/MIDDLE TENNESSEE
EARLY SUNDAY AFTERNOON...WITH SOME OF THIS ACTIVITY TRANSLATING
SOUTHEASTWARD INTO THE REGION BY LATE AFTERNOON. HOWEVER...A BROAD
REGION OF SUBSIDENT AIR ALOFT BENEATH THE ANTICYCLONIC AXIS OF A
100-120 KT UPPER JET WILL ADVECT OVER THE REGION IN ADVANCE OF THE
COLD FRONT LIMITING COVERAGE/INTENSITY OF THIS ACTIVITY. A FEW
LINGERING SHOWERS/STORMS WILL BE POSSIBLE FOR THE SOUTHEASTERN ZONES
EARLY SUNDAY EVENING...IMMEDIATELY AHEAD OF THE COLD FRONT WHICH
SHOULD PUSH THROUGH MOST OF THE REGION BETWEEN 00-06Z MONDAY.

THE BASE OF THE LONGWAVE TROUGH WILL PASS OVERHEAD ON MONDAY BUT
SHOULD NOT DISRUPT VERY PLEASANT CONDITIONS AS DEWPOINTS FALL INTO
THE UPPER 40S/LOWER 50S. IN FACT...DEWPOINTS MAY REACH THE LOWER/MID
40S MONDAY NIGHT PROVIDING LOW TEMPERATURES IN LOWER 50S...AS
CONDITIONS WILL NOT BE IDEAL FOR STRONG RADIATIONAL COOLING. FOR THE
REMAINDER OF THE EXTENDED PERIOD...THE SOUTHERN PORTION OF THIS
LONGWAVE TROUGH APPEARS TO CUTOFF ONCE AGAIN ACROSS THE SOUTHEASTERN
ATLANTIC COAST...WITH THIS LOW EXPECTED TO RETROGRADE WEST-
NORTHWESTWARD AROUND THE SOUTHERN PERIPHERY OF A MID-LEVEL HIGH
SITUATED FROM THE EASTERN GREAT LAKES ACROSS NEW ENGLAND. THIS WILL
ALLOW FOR A GRADUAL INCREASE IN CLOUD COVER...BUT LITTLE CHANCE FOR
RAIN THROUGH THE END OF NEXT WEEK.

70/DD

&&

.AVIATION...
FOR 12Z TAFS...
A WEAK BOUNDARY DRAPED ACROSS THE AREA WILL DEVELOP SHOWERS AND
STORMS IN THE VICINITY OF THE TERMINALS TODAY, WITH SLIGHTLY BETTER
CHANCES AT KMSL. SCATTERED CLOUDS THIS MORNING WILL BRIEFLY CLEAR
BEFORE THE SHOWERS AND STORMS DEVELOP BY MIDDAY, ENDING LATE THIS
EVENING. LOW CLOUDS ARE POSSIBLE HEADING INTO SATURDAY MORNING, BUT
WILL ONLY INCLUDE MVFR CEILINGS WITH THIS ISSUANCE (2500FT).

12

&&

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

$$

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


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