000
FXUS64 KHUN 161157
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
657 AM CDT THU MAY 16 2013

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 509 AM CDT THU MAY 16 2013/
MOST OF THE SENSIBLE WEATHER IMPACTS FOR THE TN
VALLEY OVER THE SHORT TERM WILL BE EITHER DIRECTLY OR INDIRECTLY
ASSOCIATED WITH A CLOSED UPR LOW NOW MOVING ACROSS THE RED RIVER
VALLEY. THIS FEATURE WAS PARTIALLY RESPONSIBLE FOR SEVERE WEATHER
INCLUDING TORNADOES JUST WEST OF THE DFW METRO YESTERDAY...BUT IS
EXPECTED TO WEAKEN AS IT MOVES TOWARD THE TN VALLEY. SEVERE WEATHER
CHANCES LOOK RATHER SMALL FOR OUR AREA THROUGH THE END OF THE WEEK
AND INTO THE WEEKEND. WEATHER CONDITIONS FOR THE PERIOD BEYOND WILL
BECOME INCREASINGLY WARM AS A RIDGE BUILDS OVER THE EASTERN CONUS.
HOWEVER...CONFIDENCE IS BUILDING FOR ANOTHER TROUGH AND PERHAPS A
SLIGHTLY COOLER AIRMASS FOR MID TO LATE WEEK. MORE DETAILS FOLLOW
BELOW.

EARLY MORNING ANALYSIS SHOWS THE MAIN BELT OF THE POLAR WESTERLIES
CONFINED TO THE CANADIAN/CONUS BORDER...WHILE THE SUBTROPICAL JET
EXTENDED ACROSS NORTH-CENTRAL MEXICO INTO THE WESTERN GOM. IN
BETWEEN...A CLOSED UPR-LOW WAS MOVING SLOWLY EWRD ACROSS THE OK/TX
BORDER REGION...WITH THE CENTER VERY NEAR OK CITY. STANDARD WATER
VAPOR IMAGERY INDICATED A REGION OF DRIER AIR WRAPPING AROUND THE
SOUTHERN FLANK OF THE LOW...WHICH WAS CORROBORATED BY 00Z SOUNDINGS
AND OTHER MULTI-SPECTRAL MODIS/VIIRS AND RGB IMAGERY. REGIONAL
RADARS AT 330 AM CDT SHOWED HEAVIER CONVECTION WAS GENERALLY
CONFINED TO PORTIONS OF AR AND TX...WHILE A FEW SHOWERS WERE LOCATED
IN THE MEMPHIS METRO AND ALONG A NARROW LINE STRETCHING FROM THE
MISS DELTA INTO SW ALABAMA. THESE SHOWERS...IN ASSOC/WITH AN AREA OF
SHEARED UPR VORTICITY WILL CONTINUE TO ADVANCE EWRD THROUGH THE
MORNING. WHILE SOME OF THE RAIN MAY BE REACHING THE SFC...SOME OF
THE LIGHTER SHOWERS ALOFT LIKELY ARE NOT REACHING THE SFC DUE TO THE
PRESENCE OF A SUBSTANTIALLY DRY MID-LAYER. THIS FEATURE WILL BE
PROGRESSIVE THROUGH THE MORNING...AND SHIFT TO OUR EAST BY THE
AFTERNOON. HOWEVER...THE MAIN UPR LOW IS LIKELY TO BECOME
INCREASINGLY SHEARED W-E AS THE DAY PROGRESSES...WITH WEAK UPR VORT
MAXIMA ROTATING THROUGH THE REGION. THE PATTERN WITH THE SUITE OF
GUIDANCE IS TOO CHAOTIC TO DISCERN A COHERENT FEATURE...BUT SUFFICE
IT TO SAY THAT LIFT ON A SYNOPTIC SCALE WILL BE PRESENT BUT LIKELY
WEAK. IN ADDITION...LOW-LEVEL FLOW LOOKS TO BE LARGELY DIFFLUENT IN
NATURE. NEVERTHELESS...GIVEN THE CLOUD TRENDS OVER THE LAST SEVERAL
HOURS...IT LOOKS AS THOUGH MORE CLEARING AND INSOLATION MAY BE
REALIZED LATER THIS AFTERNOON THAN PREVIOUSLY THOUGHT. THIS WOULD
LEAD TO GREATER DESTABILIZATION AND PRESENT A HIGHER THREAT OF
SHRA/TSTM ACTIVITY...BUT WILL RETAIN THE SLIGHT CHANCE POPS FOR TODAY
ATTM GIVEN THE OTHER COMPETING FACTORS.

ALTHOUGH THE PARENT UPR LOW IS LIKELY TO WEAKEN OVER THE NEXT COUPLE
OF DAYS...IT WILL KEEP A STEADY ADVANCE TO THE EAST. BY LATER
TONIGHT...THE MAIN CORE OF THE UPR LOW WILL PROBABLY PUSH INTO
WESTERN PORTIONS OF THE TN VALLEY. CONTINUING INSTABILITY AHEAD OF
THE FEATURE WILL LIKELY RESULT IN ANOTHER AREA OF DEEP CONVECTION IN
THE MID-MISS VALLEY LATER TODAY AHEAD OF THE UPR LOW. ALTHOUGH
STEERING FLOW WILL BE SW-W...CONVECTION MAY BE PARTIALLY COLD-POOL
DRIVEN...WITH THE POSSIBILITY FOR DEVELOPMENT INCREASING IN OUR AREA
TONIGHT. POPS WERE RAISED A LITTLE MAINLY IN THE NW TO ACCOUNT FOR
THIS SCENARIO...BUT WERE KEPT AT CHANCE CATEGORY UNTIL A CLEARER
PICTURE EMERGES. CHANCES FOR SEVERE WEATHER LOOK RATHER SMALL FOR NOW
WITH VERY LOW SHEAR AND MARGINAL CAPE.

ON FRIDAY...AS DAYTIME HEATING COMMENCES ALBEIT UNDER A DENSER CLOUD
CANOPY...THUNDERSTORM COVERAGE IS LIKELY TO INCREASE. POPS WERE
ADJUSTED UPWARD TO ACCOUNT FOR THE GREATER INSTABILITY AND SYNOPTIC
LIFT AVAILABLE. SHEAR WILL REMAIN RELATIVELY LOW WITH THIS FEATURE
AS IT MOVES ACROSS THE REGION...HOWEVER BRIEF INTENSIFICATION OF THE
LOW-LEVEL JET FRIDAY AFTERNOON INTO SAT MORNING MAY ALLOW FOR SOME
ORGANIZATION OF STORMS ALONG THE SE FLANK OF THE UPR LOW. WHILE
BETTER STORM ORGANIZATION IS MORE LIKELY TO OUR WEST OVER THE MID-
MISS VALLEY OR THE WESTERN TN VALLEY...STORMS MAY MAINTAIN
ORGANIZATION AS THEY MOVE EWRD INTO PORTIONS OF NW ALABAMA LATE
FRIDAY AFTERNOON. SCTD STRONG STORMS WILL PROBABLY PERSIST ACROSS
THE AREA INTO FRIDAY EVENING AND THE OVERNIGHT PERIOD. CONTINUED
STORM ORGANIZATION IS POSSIBLE WITH AMPLE INSTABILITY...ALTHOUGH THE
THREAT FOR SEVERE WEATHER IS LIKELY TO DECREASE WITH THE LOSS OF
DAYTIME HEATING.

KEPT POPS FOR SATURDAY AS ANOTHER UPSTREAM UPR-WAVE MOVES SWRD INTO
THE REGION...PERHAPS MERGING WITH THE PRE-EXISTING UPR TROUGH.
INSTABILITY MAY ACTUALLY BE HIGHEST ON THIS DAY...WITH CLOUD COVER
THE OBVIOUS CAVEAT. NEVERTHELESS...FORECAST CAPE VALUES EXCEEDING
2000 J/KG SUGGEST STRONG UPDRAFT POTENTIAL. WHILE SHEAR REMAINS
GENERALLY WEAK...MARGINALLY SEVERE HAIL COULD STILL OCCUR.

THE EFFECTS OF THE COMBINED UPR-LVL SYSTEMS COULD IMPACT THE AREA
THROUGH SAT NIGHT...AND PERHAPS INTO THE EARLY PART OF THE DAY ON
SUNDAY IN THE EAST. DUE TO THE UNCERTAINTY WITH THE EVENTUAL
MOVEMENT OF THE SYSTEM...A SLIGHT CHANCE POP WAS INTRODUCED IN THE
EASTERN HALF OF THE AREA FOR SUNDAY.

FOR MON-TUES...A RIDGE WILL BUILD QUICKLY IN THE EASTERN CONUS AS
THE LARGE SCALE PATTERN BECOMES INCREASINGLY AMPLIFIED. GENERALLY
HOT AND DRY WEATHER WILL LIKELY RESULT FOR THE REGION.
CURRENTLY...HIGHS IN THE MID/UPR 80S ARE FORECAST FOR MOST LOCATIONS
ON MON AND TUES. HOWEVER...SOME GUIDANCE IS INDICATING LOW 90S ARE
POSSIBLE AS EARLY AS MONDAY.

ALTHOUGH TYPICAL DIFFERENCES STILL EXIST WITH THE GLOBAL GUIDANCE
DURING THE MIDDLE OF NEXT WEEK...CONFIDENCE IS SLOWLY INCREASING
THAT A PROGRESSIVE TROUGH WILL MOVE INTO THE TN/OH VALLEY REGION BY
ABOUT WED. THIS WOULD BRING A CHANCE OF SHOWERS/TSTMS TO THE AREA
AND A CHANCE FOR COOLER CONDITIONS.

KDW

&&

.AVIATION...
FOR 12Z TAFS...VFR CONDS WILL LIKELY PERSIST AT BOTH HSV/MSL FOR THE
MAJORITY OF THE UPCOMING VALID TAF PERIOD. BKN/OVC VFR CIGS OF
AS/CS AND SOME VIRGA WILL CONTINUE TODAY...WITH LOWEST CIGS GENERALLY
14-18 KFT. CLOUD DECKS WILL BEGIN TO DESCEND EARLY THIS EVENING AS AN
UPPER- LEVEL DISTURBANCE SLOWLY APPROACHES FROM THE WEST...WITH
STRATUS CIGS POTENTIALLY FALLING TO BTWN 3-4 KFT BY END OF FORECAST
PERIOD. HAVE ALSO INCLUDED VCSH IN TAFMSL BTWN 17/06-12Z...ALTHOUGH A
FEW TSRA WILL ALSO BE PSBL -- ESPECIALLY AFTER 09Z. SFC WINDS WILL
BACK FROM SSW TODAY TO SSE OVERNIGHT...WITH SPEEDS REMAINING IN THE
5-10 KNOT RANGE.

70/DD

&&

.HUN WATCHES/WARNINGS/ADVISORIES...

AL...NONE.

TN...NONE.

&&

$$

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