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000
FXUS64 KHUN 180929
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
429 AM CDT SAT MAY 18 2013

.DISCUSSION...
WEATHER CONDITIONS HAVE BECOME MOSTLY QUIET AND
STABLE EARLY THIS MORNING ACROSS NORTHERN ALABAMA AFTER THE RAIN AND
ISOLATED THUNDERSTORMS OF YESTERDAY...ONE OF WHICH PRODUCED A COUPLE
OF BRIEF EF-0 TORNADOES. SOME RECENT DEVELOPMENT OF SHOWERS HAS
OCCURRED THOUGH IN AREAS SOUTH OF THE TN RIVER. A FEW MODIFICATIONS
WERE MADE WITH THIS LATEST FCST PACKAGE...MOSTLY TO POPS FOR TODAY
BASED ON THE LATEST TRENDS AND TO DECREASE POPS SLIGHTLY SUNDAY.
MOSTLY SMALL ADJUSTMENTS WERE MADE TO FCST ELEMENTS BEYOND
SUNDAY...WITH POPS ADDED TO TUESDAY NIGHT AND EXTENDED INTO FRIDAY
DUE TO DISCREPANCIES BETWEEN GLOBAL MODELS.

EARLY MORNING ANALYSIS SHOWS AN UPR LOW DIRECTLY OVER THE TN
VALLEY...WITH DEEP CONVECTION NOTED IN SATL AND RADAR IMAGERY
STRETCHING FROM N CENTRAL MISS ACROSS N CENTRAL AL. MOST OF THE
ACTIVITY WAS CONFINED TO AREAS BETWEEN THE TN RIVER AND THE
INTERSTATE 20 CORRIDOR...ALTHOUGH THE DEEPEST AND BEST ORGANIZED
AREA OF CONVECTION WAS LOCATED IN N CENTRAL MISS. MUCH OF THIS
APPEARS TO BE FORMING ALONG THE REMNANTS OF A LOW-LVL BAROCLINIC
BOUNDARY...MADE VISIBLE PARTLY BY A LINEAR REGION OF STRATUS CLOUD
STRETCHING NW-SE BUT ALSO BY A WEAK TEMP/DEWPOINT GRADIENT. THE
AFORE-MENTIONED UPR LOW IS OF COURSE AIDING IN CONVECTIVE
DEVELOPMENT THROUGH ASSOC QG LIFT AND ELEVATED INSTABILITY. INITIAL
THINKING WAS THAT THE UPR WAVE WOULD BE THE NEAR SOLE DRIVER OF
CONVECTION TODAY. HOWEVER...THERE HAS BEEN SOME RECENT TENDENCY FOR
A LINE OF CONVECTION TO DEVELOP SLOWLY NORTHWARD ALONG THE MOVING
BOUNDARY. THE 06Z RAP AND 00Z NAM DO SHOW STREAMLINE CONVERGENCE
SLOWLY MIGRATING NORTHWARD THROUGH THE DAY IN ASSOC/W THIS
FEATURE...ALTHOUGH THE BETTER CONVERGENCE IS MOSTLY IN THE WEST AND
APPEARS TO EVENTUALLY STALL THERE. THE POP GRADIENT FOR TODAY WAS
REVISED TO SHOW HIGHER CHANCES IN THE SOUTH...AT THE LIKELY CATEGORY
THERE GRADUALLY TAPERING OFF TO CHANCE POPS IN FAR NORTHERN AREAS.
GIVEN THE SLOW BUT PROGRESSIVE NATURE OF THE UPR LOW AND ITS CURRENT
POSITION...HIGHEST CHANCES FOR CONTINUED DEEP CONVECTION BY THIS
FEATURE WOULD BE IN THE EAST...WHILE THE LOW-LVL BOUNDARY SHOULD
RESULT IN FURTHER CONVECTION IN THE WEST. STEERING FLOW IS ALIGNED
NEARLY PARALLEL TO THE SFC BOUNDARY...WHICH IS CAUSING TRAINING OF
CELLS TO OUR SOUTH AND WEST. THIS MAY CONTINUE FOR OUR SOUTHERN AND
WESTERN COUNTIES INTO THE MORNING AS THE LINE DRIFTS SLOWLY
NORTHWARD. LOCAL INSTANCES OF FLASH FLOODING MAY OCCUR IN THE PW-
RICH ENVIRONMENT. SHEAR AND STORM ORGANIZATION WILL ACTUALLY LIKELY
BE STRONGEST THIS MORNING BEFORE SHEAR WEAKENS THIS AFTERNOON. WHILE
SHEAR WILL BE WEAK TODAY...POTENTIALLY HIGH CAPE VALUES THIS
AFTERNOON ~2500J/KG COULD RESULT IN A FEW INSTANCES OF LARGE HAIL
AND DAMAGING WIND GUSTS WITH ANY STRONGER STORMS.

SHOWER AND TSTM ACTIVITY IS LIKELY TO WANE SOMEWHAT TONIGHT WITH THE
LOSS OF DAYTIME HEATING...AND ALSO AS THE UPR WAVE BEGINS TO SHIFT
TO THE EAST. HOWEVER...AS AN UPR WAVE CURRENTLY IN THE MIDWEST MOVES
SWRD AND MERGES WITH THE LOW OVER THE TN VALLEY...FURTHER CONVECTIVE
DEVELOPMENT IS POSSIBLE. THE 00Z GFS/CANADIAN/ECMWF SUITE WERE
FAVORED OVER THE REGIONAL NAM...WHICH INDICATED A SLOWER MOVING WAVE
DIRECTLY OVER OUR AREA. GIVEN THE HIGHER CONFIDENCE IN THE MOVEMENT
OF THIS FEATURE AND THE POTENTIAL FOR CONVECTION OVER THE
AREA...POPS WERE INCREASED A LITTLE IN THE NE WHERE DEVELOPMENT IS
FAVORED. MOST OF THE CONCENTRATED SHRA/TSTM ACTIVITY THOUGH IS
LIKELY TO BE IN TN/GA.

RETAINED CHANCE POPS IN THE EAST FOR SUNDAY...MAINLY TO ACCOUNT FOR
THE DIGGING UPR WAVE. HOWEVER...POPS WERE DECREASED A LITTLE IN THE
AFTERNOON. DEPENDING ON THE AMOUNT OF CLOUD COVER...WHICH IS LIKELY
TO DECREASE DURING THE DAY...HIGHS IN THE MID/UPR 80S APPEAR LIKELY.

WARMER AIR IS STILL EXPECTED TO ENTER THE REGION AS A RIDGE BUILDS
ACROSS THE SOUTHEAST IN ADVANCE OF A BROAD TROUGH IN THE WESTERN AND
CENTRAL CONUS. WHILE SOME SENSIBLE HEATING WILL GO INTO EVAPORATION
OF RECENT RAINS AND THE AIRMASS IS LIKELY TO REMAIN HUMID...HIGHS IN
THE UPR 80S TO NEAR 90 APPEAR POSSIBLE IF NOT LIKELY. THE COMBINED
TEMPS AND HUMIDITY WILL CREATE HEAT INDICES IN THE LOW/MID 90S FOR
MANY LOCATIONS FOR THE FIRST TIME THIS WARM SEASON. DRY CONDITIONS
ARE STILL ANTICIPATED FOR MON THRU TUES.

BY TUES NIGHT...A LINE OF SHOWERS/TSTMS IS EXPECTED TO APPROACH THE
TN VALLEY FROM THE WEST...IN ADVANCE OF THE IMPENDING CDFNT. TIMING
UNCERTAINTIES REMAIN WITH THE FRONT AND THE ASSOCIATED
SHOWERS/TSTMS...BUT THERE HAS BEEN SUFFICIENT CONSISTENCY AMONG
SOLUTIONS TO REINTRODUCE POPS BACK IN THE FCST FOR TUES NIGHT FOR
MOST AREAS. THE WEST WILL SEE THE BEST CHANCES OF COURSE.

POPS WERE RAISED A LITTLE FOR WED/WED NIGHT WITH CONFIDENCE SLOWLY
INCREASING IN THE TIMING FOR THE FRONT AND ASSOCIATED IMPACTS. RIGHT
NOW...DYNAMICS WITH THE FRONT DO NOT LOOK PARTICULARLY STRONG. SO
CHANCES FOR SEVERE WEATHER APPEAR SMALL. NEVERTHELESS...THIS WILL
BEAR WATCHING.

THE POSSIBILITY STILL EXISTS THAT THE FRONT MAY INITIALLY STALL...AND
THERE IS SOME INDICATION THAT A SECONDARY FRONT AND SEASONABLY COOL
AIRMASS WILL FINALLY PUSH INTO THE REGION BY NEXT WEEKEND.

KDW

&&

.AVIATION...
/ISSUED 103 AM CDT SAT MAY 18 2013/
FOR 06Z TAFS...SCTD SHRA/TSRA WILL CONTINUE TO DEVELOP ACROSS THE
REGION THRU TOMORROW AFTN...ASSOC WITH VARIABLE CIGS. WHILE BOTH
SITES ARE CURRENTLY MVFR...IFR/ALT MINS CIGS HAVE DEVELOPED AROUND
THE SHRA/TSRA IN MS/AL. THEREFORE...DO NOT EXPECT MVFR CONDS TO
LINGER LONG. CIGS SHOULD DROP TO AT LEAST IFR OVER THE NEXT SEVERAL
HRS AND COULD DIP BELOW ALT MINS NEARING 12Z. HAVE NOT INCLUDED THIS
IN THE TAFS ATTM BECAUSE OF CHALLENGES IN TIMING THE ONSET. ADDTL
TSRA DEVELOPMENT WILL THEN OCCUR AFTER SUNRISE BUT CIGS SHOULD SLOWLY
IMPROVE THROUGH THE END OF THE PERIOD AS THIS SYSTEM SLIDES EASTWARD
AND AWAY FROM THE TERMINALS.

CCC/DD

&&

.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE    82  66  87  66 /  50  40  20  10
SHOALS        83  66  88  67 /  50  30  20  10
VINEMONT      80  66  85  66 /  60  30  20  10
FAYETTEVILLE  81  64  84  64 /  40  40  40  10
ALBERTVILLE   79  64  84  65 /  60  30  40  10
FORT PAYNE    79  65  82  64 /  70  40  50  10

&&

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

$$

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AT WEATHER.GOV/HUNTSVILLE.