Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 241414
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
914 AM CDT THU JUL 24 2014

.UPDATE...
REMOVED DENSE FOG ADVISORY AND MADE SMALL ADJUSTMENTS TO POPS.

&&

.DISCUSSION...
A WEAK CDFNT LOOKS TO BE BETWEEN MSL AND HSV. LOCAL RADARS WERE ONLY
SHOWING A FEW SHRA OVER PORTIONS OF MID TN ATTM. WATER VAPOR STLT
SHOWED VERY DRY AIR IN THE MID/UPPER LAYERS OF THE ATMOSPHERE...THAT
HAS PUSHED ACROSS THE TN VALLEY. TIME SECTIONS/MODEL SOUNDINGS/12Z
U/A SOUNDINGS ALL SHOWED LIMITED MOISTURE FOR THE CDFNT TO WORK WITH
AS IT MOVES ACROSS THE CWA TODAY. THE BEST CHC OF PCPN WILL BE OVER
OUR SERN ZONES (LATE MRNG/AFTN) AS THE CDFNT MOVES EAST AND THE
EFFECT OF DAYTIME HEATING. NO SVR WX EXPECTED TODAY BUT A FEW STORMS
MAY PRODUCE GUSTY WINGS AND BRIEF HVY RAIN.

07

&&

.AVIATION...
/ISSUED 619 AM CDT THU JUL 24 2014/
FOR 12Z TAFS... LOW CLOUDS AND AREAS OF FG WITH PERIODIC REDUCTIONS
IN VSBY TO IFR WILL OCCUR ALONG THE TN RIVER THRU ~14Z. THE CLOUDS
WILL LIFT INTO A SCT-BKN CUMULUS LAYER LATE THIS MORNING. ISOLD/SCT
SHRA AND TSRA SHOULD DEVELOP, BUT THE PROB IS TOO LOW TO INCLUDE IN
THE PREVAILING FORECAST ATTM. A COOL FRONT WILL SHIFT WINDS TO THE N
THIS AFTN AND EVENING WITH A CLEARING TREND AND VFR CONDS EXPECTED.

AK

&&

.PREV DISCUSSION...
/ISSUED 352 AM CDT THU JUL 24 2014/
THE ANOMALOUS JULY PATTERN CONTINUES, WITH A RELATIVELY WEAK SURFACE
COLD FRONT SITTING JUST NORTH OF THE HUN CWFA AT 08Z. THIS WAS BEING
MARKED BY A CLUSTER OF SHOWERS AND THUNDERSTORMS AROUND MIDNIGHT, BUT
THIS HAS SINCE DISSIPATED DESPITE THE PRESENCE OF A MID-LEVEL
SHORTWAVE. WITH THE DISSIPATION OF THE CONVECTION, THE FOCUS NOW
SHIFTS TO FOG, AS SEVERAL LOCATIONS HAVE SEEN VISIBILITY RAPIDLY DROP
OFF WITH CLEARING. THERE IS LITTLE DRY AIR ADVECTION OCCURRING
IMMEDIATELY BEHIND THE FRONT; LOWER DEWPOINTS ARE STILL SITTING
ROUGHLY ALONG THE TN-KY STATE LINE.

BASED UPON CURRENT OBSERVATIONS AND CLEARING SKIES, AND THE FAIRLY
WIDESPREAD PRECIPITATION YESTERDAY, DENSE FOG SHOULD BECOME AN
INCREASING PROBLEM AS WE APPROACH SUNRISE. SO WE WILL ISSUE A DENSE
FOG ADVISORY, WHICH WILL BE IN EFFECT THROUGH 9 AM.

NEAR-TERM MODELS HAVE HAD A FAIRLY GOOD HANDLE ON THE CONVECTION
SITUATION THIS MORNING, WITH SEVERAL INDICATING THE HUN CWFA GETTING
SPLIT BY WEAKENING/DISSIPATING CONVECTION TO THE NORTH (AS HAPPENED
BETWEEN 12-2AM) AND STORMS THAT RE-FIRE LATER TODAY TO THE SOUTH.
CONSIDERING THE MID/UPPER-LEVEL DRY AIR RAPIDLY PUSHING INTO THE
AREA (PER WATER VAPOR), THIS SCENARIO IS LOOKING MORE AND MORE
REASONABLE. SO FORECAST POPS FOR TODAY WILL EMPHASIZE THE MORNING
HOURS, ANTICIPATING THE ARRIVAL OF DRIER AIR FOR AFTERNOON, AND SKEW
HIGHER TO THE SOUTH AND EAST WHERE MOISTURE WILL LINGER THE LONGEST.
HIGHS TODAY ARE TOUGH, AS ADVECTION IS NOT EXPECTED TO BE COLD AS
MUCH AS DRY; SO MOS CONSENSUS OF UPPER 80S LOOKS GOOD.

THE REST OF THE SHORT TERM SHOULD BE DRY AS DRY MID/UPPER-LEVEL AIR
SETTLES IN OVER THE REGION. NIGHT TIME TEMPERATURES WILL REMAIN BELOW
NORMAL IN LIGHT OF DRIER-THAN-NORMAL DEWPOINTS AND DECENT RADIATIONAL
COOLING, BUT HIGH TEMPERATURES WILL QUICKLY RISE DUE TO GOOD
INSOLATION AND DRY AIR. IN FACT, THE MOS CONSENSUS PUSHES HIGHS INTO
THE MID AND UPPER 90S SATURDAY AS MID-LEVEL RIDGING MAKES A BRIEF
ATTEMPT TO BUILD OVER THE MID-SOUTH. HOWEVER, THE GFS HAS AVERAGED
2-4 DEGREES TOO WARM THIS SUMMER (THE NAM WARM BIAS IS LESS
PRONOUNCED BUT STILL EXISTS) SO THE FORECAST WILL UNDERCUT THE MOS.

THE FLIRTATION WITH THE HEAT AND HUMIDITY WILL BE SHORT-LIVED, AS
ANOTHER ANOMALOUSLY DEEP (3-4 STANDARD DEVIATIONS BELOW NORMAL)
TROUGH IS EXPECTED TO DIG OVER THE EASTERN CONUS SUNDAY-MONDAY, WITH
THE SURFACE FRONT PROGGED TO PASS ACROSS THE HUN CWFA MONDAY MORNING.
THIS WILL MEAN ANOTHER SURGE OF INCREASED RAIN/STORM POTENTIAL,
THOUGH THE OVERNIGHT ARRIVAL MAY LIMIT COVERAGE. THE MESOSCALE SETUP
IS TYPICAL FOR JULY--DECENT INSTABILITY BUT LITTLE SHEAR.

BEHIND THE FRONT, ONCE AGAIN, A DRY FORECAST IS EXPECTED FOR THE
REST OF THE FORECAST PERIOD (THROUGH WEDNESDAY) AS DRIER AIR
ASSOCIATED WITH THE TROUGH SETTLES IN OVER THE AREA. HIGH
TEMPERATURES SHOULD FALL BACK (AGAIN) TO 5-10 DEGREES BELOW NORMAL
WITH LOWS 10-15 DEGREES BELOW NORMAL. THE GFSX MOS SEEMS TOO WARM IN
THIS REGIME, AND HAVE TRENDED TOWARDS A MODIFIED PERSISTENCE BASED ON
SIMILAR PATTERNS FROM EARLIER THIS SUMMER.

BCC

&&

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

$$

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


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