Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 012343 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
643 PM CDT FRI AUG 1 2014

.UPDATE...
FOR 00Z TAFS

&&

.DISCUSSION...
/ISSUED 238 PM CDT FRI AUG 1 2014/
THE MID-LEVEL SHORTWAVE TROUGHS AND EMBEDDED UNDULATIONS WILL BE
PUSHING ACROSS THE MS RIVER VALLEY OVER THE NEXT 24-48 HOURS BRINGING
THE POSSIBILITY OF SHOWERS AND THUNDERSTORMS STARTING THIS EVENING
INTO TONIGHT. IT DOES APPEAR THAT THE TN VALLEY WILL REMAIN ON THE
DRIER SIDE WITH DRY AIR ADVECTION APPARENT ON WV IMAGERY AHEAD OF THE
NE/MO SHORTWAVE THIS EVENING. DID KEEP AN ISOLATED CHANCE OF SHOWERS
IN THIS EVENING TO ACCOUNT FOR ANY LINGERING ACTIVITY ALREADY
OCCURRING, BUT THE PRIMARY THREAT WILL BE EARLY TOMORROW MORNING AS
MOISTURE ADVECTS NORTHEAST AHEAD OF THE SHORTWAVE TROUGH WITH MORNING
LOW CLOUDS POSSIBLE OVER NE AL. A GRADIENT IN TSRA COVERAGE IS
EXPECTED WITH THE MOISTURE AXIS AND LIFT FOCUSED MAINLY OVER NE AL TO
W CENTRAL AL. THUS, INTRODUCED THE GRADIENT IN THUNDERSTORM CHANCES
FROM NW TO SE WITH HIGHER POPS OVER THE SE SIDE OF THE CWA (DEKALB,
MARSHALL, CULLMAN COUNTIES) MAINLY FOR SCT THUNDERSTORMS AT TIMES
THROUGH THE DAY. INSTABILITY IS WEAK WITH SBCAPES BTWN 500-700 J/KG
(UP TO 1000 J/KG ON NAM) BUT STILL ENOUGH FOR GENERAL THUNDERSTORM
ACTIVITY.

THERE IS EVIDENCE OF AN ADDITIONAL CHC FOR THUNDERSTORMS AS AN
ANOTHER AMPLIFYING SHORTWAVE TROUGH TRAVERSES THE MS RIVER VALLEY ON
SAT NIGHT INTO SUN, BUT HAVE ONLY KEPT LOW END ISOLATED TO SCT
THUNDERSTORM THREAT MAINLY ON SAT NIGHT. THE VERTICAL PROFILE
APPEARS TO DRY QUICKLY ON SUNDAY WITH MOST OF THE FORCING AND
MOISTURE RETURN TO THE S AND SE OF THE TN VALLEY. DRY AIR ADVECTION
DOES LOOK POSSIBLE ON SUNDAY INTO MONDAY AS A WEAK SFC FRONT
MEANDERS OVER THE TN VALLEY. HOWEVER, AM NOT COMPLETELY CONVINCED
THAT THE DEWPOINTS WILL DROP QUITE AS MUCH AS SOME OF THE CURRENT
GUIDANCE SUGGESTS, AND THIS LOOKS SHORT-LIVED. NEVERTHELESS, WITH
THE UPPER NW FLOW INDICATED BY THE GFS/ECMWF/CANADIAN, COULD SEE
SOME MIXING DOWN OF DRY AIR ESPECIALLY ON MONDAY AND TUESDAY.

BY MONDAY THROUGH WEDNESDAY, THE MODELS DIVERGE SOMEWHAT ON THE
UPPER FLOW PATTERN TRANSITION WITH THE ECMWF SHOWING A LESS
AMPLIFIED TROUGH OVER THE EASTERN HALF OF THE COUNTRY WHILE GFS
SHOWS A MORE AMPLIFIED TROUGH AND A BUILDING RIDGE TO THE WEST. FOR
NOW, HAVE LEFT THIS TIME PERIOD DRY AND RETAINED CLIMO SCHC POPS ON
THU/FRI WITH A HINT OF A SHORTWAVE TROUGH MOVING ACROSS THE REGION.
IN ADDITION, MADE SOME SLIGHT ADJUSTMENTS TO TEMPERATURES IN THE
EXTENDED BUT MAINLY KEPT CLIMO LOW 90S AS HIGHS AND MID TO UPPER
60S AS LOWS.

SL.77

&&

.AVIATION...
FOR 00Z TAFS...LINGERING WEAK CONVECTION ALONG A SFC TROUGH DRAPED
ACROSS ERN TN INTO NE AL...CONTINUES TO GRADUALLY DIMINISH NEAR THE
KHSV TERMINAL. THIS SHOULD TRANSLATE INTO VFR CONDS FOR THE TWO MAIN
AIRPORTS AT LEAST INTO THE OVERNIGHT HRS. LATEST GUIDANCE IS HINTING
AT SOME -BR OR BRIEF/TEMPO MVFR VIS DEVELOPING GOING INTO THE EARLY
MORNING HRS SAT...AND THIS IS REFLECTED FOR A FEW HRS IN THE TAF
PRODUCTS. SCT CONVECTION OR SHRA/TSRA ARE THEN XPCTED TO DEVELOP IN
RESPONSE TO A CONTINUED PRESENCE OF WEAK UPPER DISTURBANCES ROTATING
EWD ACROSS THE REGION HEADING INTO THE LATE MORNING PERIOD...ALTHOUGH
TIMING/PLACEMENT WILL PROVE DIFFICULT GIVEN THE SUBTLE NATURE OF
THESE PASSING WAVES.

09

&&

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

$$

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



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