Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 231118 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
618 AM CDT THU OCT 23 2014

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 440 AM CDT THU OCT 23 2014/
ANOTHER QUIET AND COOL NIGHT IS IN PROGRESS ACROSS NORTHERN ALABAMA
AND SOUTHERN MIDDLE TENNESSEE...WITH NORMALLY IDEAL ENVIRONMENTAL
CONDITIONS FOR RADIATIONAL COOLING BEING DISRUPTED BY LIGHT NORTHEAST
WINDS. DESPITE THE PRESENCE OF A WELL-MIXED BOUNDARY LAYER...
TEMPERATURES HAVE STILL MANAGED TO FALL INTO THE MID 30S WHERE WINDS
HAVE DIMINISHED. THUS...WILL RETAIN PATCHY VALLEY FOG FOR THE ENTIRE
REGION AND PATCHY FROST FOR THE NORTHEASTERN QUADRANT OF THE FORECAST
AREA -- ALTHOUGH AM SKEPTICAL ABOUT BOTH AT THIS POINT.

FOR THE REMAINDER OF THE MORNING...SHORT TERM MODELS SUGGEST THAT A
HIGH AMPLITUDE MID-LEVEL RIDGE WILL SHIFT EASTWARD ACROSS THE
REGION BETWEEN A CUTOFF UPPER LOW OFF THE COAST OF NEW ENGLAND AND A
WEAKER UPSTREAM SHORTWAVE TROUGH TRACKING EASTWARD ACROSS SOUTHERN
CANADA AND THE NORTHERN PLAINS. BY AFTERNOON...WINDS ALOFT WILL BACK
TO THE SOUTHWEST AS THE SOUTHERN PORTION OF THE TROUGH AXIS BEGINS TO
APPROACH THE REGION AND THIS WILL ALLOW FOR A NOTICEABLE INCREASE IN
MID/HIGH-LEVEL CLOUD COVER -- POSSIBLY AS EARLY AS THIS AFTERNOON BUT
MAINLY THIS EVENING/OVERNIGHT. ALTHOUGH SOME VIRGA WILL CERTAINLY BE
POSSIBLE IN THIS REGIME...WEAK NATURE OF TROUGH AND ASSOCIATED LIFT
COUPLED WITH VERY DRY AIR BELOW 700 MB WILL LIMIT THE THREAT FOR EVEN
SPRINKLES. DESPITE WEAKER COLD ADVECTION AND 850 MB TEMPERATURES
APPROXIMATELY 3-5 DEGREES WARMER THAN YESTERDAY...THE INCREASE IN
CLOUD COVER AND SHALLOW MIXING LAYER WILL YIELD HIGH TEMPERATURES
NEAR OR SLIGHTLY COOLER THAN YESTERDAY. CONVERSELY...LOWS TONIGHT
WILL BE SEVERAL DEGREES WARMER THAN CURRENT TEMPERATURES BASED ON
EXPECTED AMOUNT OF CLOUD COVER -- WITH THREAT FOR VALLEY FOG BEING
RELATIVELY LOW. MODELS SUGGEST THAT THE MID-LEVEL TROUGH WILL SPREAD
RAPIDLY SOUTHEASTWARD AND OFF THE SOUTHEASTERN ATLANTIC COAST BY
SATURDAY MORNING AS HEIGHTS BEGIN TO RISE RATHER SUBSTANTIALLY OVER
THE SOUTHERN PLAINS. A STRONG NORTHWEST FLOW PATTERN WILL BE IN PLACE
FROM FRIDAY-SATURDAY WITH DRY CONDITIONS AND LITTLE FLUCTUATION IN
TEMPERATURES...WITH THE EXCEPTION OF SATURDAY WHEN A SLIGHTLY
STRONGER WESTERLY COMPONENT TO LOW-LEVEL FLOW WILL BOOST HIGHS BY
3-7 DEGREES. WITH SURFACE RIDGE ORIENTED DIRECTLY ACROSS THE REGION
SATURDAY MORNING...IT APPEARS A HIGHER THREAT FOR FOG WILL EXIST IN
VALLEYS AND NEAR BODIES OF WATER.

IN THE EXTENDED PERIOD...MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT
IN FORECASTING THE CENTER OF A STRONG SUBTROPICAL RIDGE TO SHIFT
SLOWLY EASTWARD FROM THE SOUTHERN PLAINS TO THE FLORIDA PENINSULA BY
MONDAY MORNING -- AS A DEEPER LONGWAVE TROUGH MOVES EASTWARD INTO THE
NORTHERN/CENTRAL ROCKIES. THUS...EXPECT GRADUAL HEIGHT RISES ALOFT
TO LEAD TO WARMER TEMPERATURES THROUGH THE END OF THE WEEKEND. A
RETURN TO SOUTHWEST FLOW ALOFT WILL MAINTAIN THE WARMING TREND EARLY
NEXT WEEK...AS THE LONGWAVE TROUGH SHIFTS FURTHER EASTWARD INTO THE
CENTRAL PLAINS AND THE SUBTROPICAL RIDGE BECOMES ESTABLISHED OFF THE
SOUTHEASTERN ATLANTIC COAST. LATEST VERSIONS OF THE GFS/ECMWF ARE NOW
IN BETTER AGREEMENT IN FORECASTING THE CORE OF THE LONGWAVE TROUGH TO
SHEAR APART AND LIFT NORTHEASTWARD INTO THE GREAT LAKES...ALLOWING A
WEAK COLD FRONT TO DRIFT SOUTHWARD INTO THE REGION TUESDAY NIGHT AND
WEDNESDAY. MOISTURE RETURN IN ADVANCE OF THE FRONT WILL BE
SUFFICIENT TO WARRANT AT LEAST CHANCE POPS -- AND ALTHOUGH MID-LEVEL
LAPSE RATES APPEAR TO BE RATHER WEAK WE WILL INCLUDE THUNDERSTORMS IN
THE GRIDS. DEEP-LAYER SHEAR AROUND 40 KNOTS WILL SUPPORT THE
POTENTIAL FOR STORM ORGANIZATION...AND IF INSTABILITY IS GREATER
THAN CURRENTLY ANTICIPATED THEN A FEW STRONG STORMS WILL BE POSSIBLE.
THERE ARE SOME INDICATIONS THAT THE COLD FRONT MAY STALL SOUTH OF THE
REGION LATE NEXT WEEK...WITH CLOUDS AND PERHAPS SOME LIGHT RAIN
POSSIBLE THURSDAY/FRIDAY.

70/DD

&&

.AVIATION...
FOR 12Z TAFS...
VFR CONDITIONS WILL PREVAIL THROUGH 12Z/24. MID AND HIGH LEVEL
MOISTURE WILL INCREASE THROUGH THE DAY/EVENING BUT THIS WILL RESULT
IN CIGS BTWN 12-15K FT. NO IMPACTS TO AVIATION ATTM.

DJN.83

&&

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

$$

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



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