Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 301357 AAB
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
857 AM CDT SUN AUG 30 2015

.UPDATE...
TO ADJUST AFTERNOON POPS AND TEMPS.

&&

.DISCUSSION...
MORNING WATER VAPOR LOOP SHOWS A CLOSED UPPER LOW CIRCULATION ACROSS
THE WESTERN FLORIDA PANHANDLE INTO EXTREME SOUTHERN ALABAMA. THIS
FEATURE WAS LIFTING SLOWLY TO THE NORTH. DEEP TROPICAL MOISTURE WAS
NOTED FROM SOUTH OF THE CAYMANS NORTH THROUGH THE FLORIDA PENINSULA
AND WRAPPING AROUND THE AFOREMENTIONED UPPER LOW ACROSS PORTIONS OF
THE TENNESSEE VALLEY AND MID SOUTH REGION.

AT THE SURFACE...THERE IS A WEAK REFLECTION OF THE UPPER LOW WITH AN
INVERTED TROUGH AXIS EXTENDING FROM THE NORTH CENTRAL GULF THROUGH
NORTHEAST ALABAMA INTO THE SOUTHERN APPALACHIANS. 12Z RAOB FROM KBMX
SHOWS A VERY MOIST (PWATS AROUND 1.8") AND DEEPLY SATURATED AIRMASS.
GENERALLY LIGHT RAINFALL HAS BEEN ROTATING CYCLONICALLY AROUND THE
NORTHERN PERIPHERY OF THE UPPER LOW FOR SEVERAL HOURS WITH SOME
DEEPER CONVECTION NOTED IN THE EASTERN QUADRANT WHERE
INSTABILITY/LAPSE RATES ARE ENHANCED.

MAIN QUESTION MARKS FOR TODAY CERTAINLY SURROUND CONTINUATION OF
RAINFALL, POTENTIAL FOR THUNDERSTORMS, AND ASSOCIATED TEMPERATURE
TRENDS. THE HRRR INDICATES A MARKED DECREASE IN PRECIPITATION OVER
THE NEXT SEVERAL HOURS AS THE FORCING WITH THE UPPER LOW SHIFTS
EASTWARD WITH TIME. HOWEVER, THE 12Z NAM STILL SHOWS RATHER
SATURATED CONDITIONS AND IN FACT INCREASES THE PWAT VALUES TO NEAR 2"
THROUGH LATE AFTERNOON. HAVING SAID THAT, NONE OF THE MODELS ARE
EXACTLY HANDLING THE CURRENT PRECIP TRENDS RATHER WELL. ALSO, BASED
ON SATELLITE TRENDS THE MODELS SEEM TO HAVE A BIT TOO EASTERLY OF A
TRACK WITH THE UPPER LOW.

BASED ON CURRENT RADAR/DIAGNOSTIC TRENDS, AM INCLINED TO INCLUDE
RATHER HIGH POPS THROUGH THE AFTERNOON FOR MAINLY RAIN/SHOWERS
WITH VERY LOW THUNDER POTENTIAL. MAY ALSO NEED TO ADJUST MAX TEMPS
DOWN AS WELL AS CLEARING POTENTIAL LOOKS MINIMAL. WILL REVIEW 14Z
TRENDS BEFORE MAKING FINAL DECISION.

15

&&

.AVIATION...
/ISSUED 617 AM CDT SUN AUG 30 2015/
FOR 12Z TAFS...RAIN IS CONTINUING TO MOVE SE TO NW TOWARDS THE
TERMINALS THIS MORNING. LIGHT RAIN WILL START AND POCKETS OF MODERATE
RAIN ARE LIKELY THROUGH THE LATE MORNING HOURS. ANY THUNDERSTORMS
WILL BE TOO ISOLATED TO INCLUDE IN THE TAFS. IN MODERATE TO HEAVY
RAIN SHOWERS CIGS MAY DROP BRIEFLY TO MVFR LEVELS BUT SHOULD
GENERALLY REMAIN VFR THROUGH AT 6-7Z MONDAY. AFTER THAT...CIGS/VIS
MAY GET DOWN TO IFR LEVELS IN FOG/LOW STRATUS BUT CONFIDENCE IS TOO
LOW THIS FAR OUT TO FORECAST THAT...WILL GO WITH BKN030/4SM BUT THIS
COULD CHANGE WITH THE NEXT UPDATE.

LN

&&

.PREV DISCUSSION...
/ISSUED 306 AM CDT SUN AUG 30 2015/
EARLY THIS MRNG THERE IS A WEAK UPPER LOW CIRCULATION OVER THE
FLORIDA PANHANDLE ALONG WITH AN UPPER TROF OVER PORTIONS OF THE OHIO
VALLEY. COLDER CLOUD TOPS/CONVECTION/HVY RAIN ASSOCIATED WITH THE
REMNANTS OF ERIKA ARE CURRENTLY MOVING NORTH ALONG THE SERN
COASTLINE. CLOSER TO HOME THERE IS A LARGE BAND OF MAINLY SHRA WITH A
FEW EMBEDDED TSRA E/SE OF THE BHM AREA...MOVING TOWARDS THE TN
VALLEY. THIS PCPN IS ASSOCIATED MORE WITH THE WEAK UPPER LOW.

FOR TODAY WILL GO WILL HIGH POPS FOR LOCATIONS ALONG AND EAST OF
I65. WILL PUT HIGH CHC POPS (50%) ACROSS EXTREME NW AL. THE WEAK
UPPER LOW WILL CONTINUE TO MOVE NE TODAY AS IT BEGINS TO OPEN UP BY
TONIGHT. THIS WILL ALLOW THE CHC OF PCPN TO TAPER OFF ACROSS THE CWA
TONIGHT. CAPES/WIND SHEAR VALUES WILL BE VERY LOW TODAY/TONIGHT AND
ALONG WITH A SATURATED ATMOSPHERE...NOT EXPECTING WIDESPREAD TSRA.
THUS FOR NOW WILL GO WITH ISOLATED TSRA FOR TODAY AND TONIGHT. NO
SEVERE WX EXPECTED BUT LOCALIZED HVY RAIN AND GUSTY WINDS WILL BE
POSSIBLE. OTHERWISE WITH CLOUDS/PCPN...TEMPS MAY NOT GET OF OUT THE
70S FOR MANY LOCATIONS. THE BEST CHC OF REACHING THE LOWER 80S WILL
BE OVER NW AL WHERE THE CHC OF PCPN IS NOT THAT GREAT.

AN UPPER RIDGE WILL BUILD ACROSS THE REGION FOR THE PERIOD TUESDAY
THRU SATURDAY. AS A RESULT BOTH THE GFS/ECMWF ARE SHOWING LOW CHANCES
OF PCPN ALONG WITH WARMER TEMPS. DAYTIME HIGHS DURING THIS TIMEFRAME
WILL BE IN THE LOWER 90S WITH MRNG LOWS ARND 70. AS FOR THE CHC OF
PCPN WILL KEEP SLIGHT POPS IN MAINLY FOR THE AFTN HOURS.

007

&&

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

$$

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



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