Area Forecast Discussion
Issued by NWS Huntsville, AL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS64 KHUN 251123 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
623 AM CDT FRI JUL 25 2014

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 440 AM CDT FRI JUL 25 2014/
A MODERATELY STRONG NORTHWEST FLOW ALOFT PREVAILS ACROSS THE CENTRAL
TENNESSEE VALLEY THIS MORNING...WITH THE MID-LEVEL TROUGH AXIS NOW
LOCATED TO THE SOUTHEAST OF THE LOCAL AREA. THIS HAS TRANSLATED TO
VERY PLEASANT EARLY MORNING TEMPERATURES/DEWPOINTS FOR LATE
JULY...WITH PATCHY VALLEY FOG LEADING TO VISIBILITY REDUCTIONS
GENERALLY IN THE 3-5 MILE RANGE.

DURING THE PERIOD FROM TODAY THROUGH SATURDAY...MODELS REMAIN
CONSISTENT IN FORECASTING A STRONG SUBTROPICAL RIDGE -- CURRENTLY
CENTERED ACROSS NEW MEXICO AND THE TEXAS PANHANDLE -- TO BUILD
EASTWARD OVER THE CENTRAL PLAINS AND INTO THE LOWER MISSISSIPPI
VALLEY. SUBSTANTIAL HEIGHT RISES ALOFT WILL RESULT IN THE DEVELOPMENT
OF A PRONOUNCED INVERSION IN THE 850-800 MB LAYER...WHICH WILL WORK
IN TANDEM WITH THE DRY AIRMASS IN PLACE TO LIMIT PRECIPITATION
CHANCES TO A SILENT 5 PERCENT. A COUPLE OF WEAK VORTICES DROPPING
SOUTHWARD IN THE NORTHERLY FLOW ALOFT MAY BRING PERIODS OF ENHANCED
HIGH-LEVEL CLOUDS COVER TO THE REGION TODAY/TONIGHT...BUT WE ARE
GENERALLY EXPECTING MOSTLY CLEAR SKIES WITH THE EXCEPTION OF
SCATTERED CUMULUS THIS AFTERNOON. BASED ON THIS REASONING...HIGH
TEMPERATURES TODAY WILL LIKELY RISE TO AROUND 90 FOR ALL BUT THE
HIGHER TERRAIN LOCATIONS...WITH WIDESPREAD HIGHS IN THE LOWER/MID 90S
SATURDAY AND SUNDAY. FORTUNATELY...DEEP BOUNDARY LAYER MIXING IS
EXPECTED ON SATURDAY AND SHOULD PREVENT SIGNIFICANT CONCERNS FOR HIGH
HEAT INDEX VALUES.

LITTLE CHANGE IN THIS PATTERN IS ANTICIPATED UNTIL SATURDAY NIGHT...
WHEN A POWERFUL MID-LATITUDE TROUGH WILL DIG SOUTHEASTWARD INTO THE
NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY -- FORCING THE SUBTROPICAL
RIDGE TO RETROGRADE WESTWARD INTO THE SOUTHERN ROCKIES. SEVERAL OF
THE GLOBAL MODELS SUGGEST AT LEAST A GLANCING IMPACT FROM A WELL-
DEFINED VORTICITY MAX...WHICH IS PROGGED TO BE ROUNDING THE NORTHERN
PERIPHERY OF THE RIDGE AND MOVING EASTWARD ACROSS KANSAS/MISSOURI ON
SATURDAY. THIS FEATURE OR ITS REMNANTS MAY SHIFT SOUTHEASTWARD ACROSS
NORTHERN ALABAMA ON SUNDAY...PERHAPS PROVIDING ENOUGH FORCING FOR
UVM TO ERODE THE CAP -- ESPECIALLY AS AFTERNOON TEMPERATURES RISE
INTO THE LOWER/MID 90S AND LOW-LEVEL DEWPOINTS INCREASE INTO THE
LOWER 70S. THUS...WE HAVE DECIDED TO INCLUDE A 20 POP FOR ISOLATED
CONVECTION SUNDAY AFTERNOON. POINT FORECAST SOUNDINGS FROM THE
NAMBUFR/GFSBUFR/ECMWF INDEED SHOW THE CAPPING INVERSION WEAKENING
AND LIFTING SUNDAY AFTERNOON. IN THE ABSENCE OF CONVECTION...HEAT
INDEX VALUES WILL BE DANGEROUSLY HIGH IN THE 100-105 DEGREE RANGE.

MODELS SUGGEST THAT THE MID-LATITUDE TROUGH OVER THE UPPER
MISSISSIPPI VALLEY AT THE BEGINNING OF THE EXTENDED PERIOD WILL
CONTINUE TO DIG SOUTHEASTWARD OVER THE GREAT LAKES BEFORE ASSUMING A
NEGATIVE TILT OVER THE EASTERN GREAT LAKES REGION BY 00Z TUESDAY. A
STRONG SURFACE COLD FRONT ASSOCIATED WITH THIS FEATURE WILL SHIFT
SOUTHWARD...REACHING SOUTHERN MIDDLE TENNESSEE BY 12Z MONDAY.
THUNDERSTORMS WILL INCREASE FROM LATE SUNDAY NIGHT THROUGH MONDAY AS
THE COLD FRONT PUSHES SOUTHWARD OVER THE LOCAL AREA...WITH FORECAST
SOUNDINGS CONTINUING TO SUGGEST AN ELEVATED THREAT FOR STRONG/SEVERE
STORMS DURING THIS PERIOD. A DRY NORTHWEST FLOW ALOFT WILL PREVAIL
FOR THE REMAINDER OF THE EXTENDED PERIOD...WITH UNSEASONABLY COOL
HIGHS IN THE LOWER 80S AND LOWS IN THE UPPER 50S/LOWER 60S.

70/DD

&&

.AVIATION...
FOR 12Z TAFS... IFR/MVFR VSBYS DUE TO BR WILL IMPROVE TO VFR RAPIDLY
BY 14Z. VFR CONDITIONS AND LIGHT FLOW ARE ANTICIPATED THE REST OF THE
PERIOD.

AK

&&

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

$$

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



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.