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Area Forecast Discussion

255
FXUS64 KHUN 171902
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
202 PM CDT FRI APR 17 2015

.DISCUSSION...
STRATIFORM -RA CONTINUES TO EXPAND EARLY THIS AFTERNOON IN ADVANCE
OF THE APPROACHING SHORTWAVE CROSSING THE MS RIVER. THUS FAR, NO
LIGHTNING HAS OCCURRED IN OUR AREA WITH UNSTABLE AIR CONFINED TO
AREAS SW OF THE WEDGE FRONT IN CENTRAL MS INTO SRN AL. DRY AIR IN
THIS AREA IS ALSO AIDING MID LEVEL LAPSE RATES. ATTM, TS APPEAR TO BE
A VERY LOW THREAT, SO HAVE KEPT THEM OUT OF THE EVENING FORECAST AS
THIS WAVE MOVES ACROSS. THE BEST LIFT EXITS BY 00Z, BUT WE`LL HAVE
LINGERING -RA/SHRA MAINLY IN OUR EASTERN COUNTIES. DRIER NERLY FLOW
IN MID LEVELS WILL ALLOW FOR PARTIAL CLEAR TO TAKE PLACE LATER
TONIGHT. THIS MAY SET UP A PRETTY DECENT ENVIRONMENT FOR FOG TO
DEVELOP IF SFC WINDS CAN DROP OFF. FOR NOW, WENT WITH PATCHY FOG FROM
06-12Z.

MID TO UPPER LEVEL RIDGING ARRIVES ON EARLY SATURDAY AS NELY LOW LEVEL
FLOW DRIES THE ATMO OUT TEMPORARILY. DESPITE SOME EARLY SUNSHINE,
HAVE GONE CLOSER TO THE COOLER GFS MOS TEMPS. SFC FLOW BECOMES SELY
DURING THE AFTERNOON WITH S-SWLY FLOW DEVELOPING THRU 850 MB.
ISENTROPIC LIFT WILL PRODUCE STRATIFORM PRECIP INITIALLY THRU EARLY
SATURDAY EVENING. AS THE CO LOW FINALLY EMERGES INTO THE PLAINS AND
LOWER MO VALLEY, DIVERGENT MID-UPPER FLOW WILL INCREASE UVVS
SUBSTANTIALLY LATE SATURDAY NIGHT INTO SUNDAY MORNING OVER THE TN
VALLEY. WIDESPREAD SHRA AND TSRA ARE EXPECTED (INITIALLY ELEVATED) TO
OVERSPREAD THE AREA AS THE LLJ OF 40-50KT INCREASES MOISTURE
TRANSPORT. THE NAM SIGNALS A DEFINED SFC-PRESSURE WAVE (POSSIBLE
QLCS) FROM 09-12Z WHICH MAY BE SFC-BASED. 2KM BULK SHEAR VALUES WILL
BE INCREASING TO 30-35KT ALONG THIS LINE, SO WE MAY HAVE A MARGINAL
THREAT OF DAMAGING WINDS. AN EVIDENT DRY SLOT WILL LIKELY SWEEP THE
QLCS/TRAILING STRATIFORM PRECIP OUT OF THE AREA RATHER QUICKLY EARLY
SUNDAY MORNING. MOST OF THE DAY MAY BE DRY AND WARM ON SUNDAY. THE
ATMO MAY REMAIN TOO STABLE UNTIL VERY LATE IN THE DAY FOR
REDEVELOPMENT. THE LACK OF CONVERGENCE SHOULD ALSO LIMIT TSRA
REDEVELOPMENT UNTIL ANOTHER WEAK SHORTWAVE ARRIVES DURING THE EVENING
HOURS (AND THIS IS STILL UNCERTAIN). THE BETTER CHC WILL HOLD OFF
UNTIL A STRONG WAVE ARRIVES LATER SUNDAY NIGHT INTO EARLY MONDAY WHEN
THE COLD FRONT MOVES IN. HODOGRAPHS WHICH ARE INITIALLY LINEAR
BECOME MUCH MORE STRONGLY CURVED AS LOW LEVEL WINDS BACK AND INCREASE
IN RESPONSE TO THE LLJ LATER SUNDAY NIGHT. THE ONE NEGATIVE FACTOR
FOR WIDESPREAD SIGNIFICANT SEVERE IS THE WEAK UPPER LEVEL JET SPEEDS
OVER THE REGION. THE STRONGER JET CORE WILL REMAIN ACROSS THE WESTERN
AND CENTRAL GULF COAST.

A WELCOME DRY PERIOD FOLLOWS EARLY NEXT WEEK UNTIL A CP HIGH DROPS
THRU THE PLAINS INTO THE DEEP SOUTH. THE MEDIUM RANGE MODELS THEN
DIVERGE WRT HANDLING OF THE WNWLY UPPER FLOW PATTERN AND A FRONTAL
BOUNDARY MOVING SE INTO THE REGION BY MID TO LATE NEXT WEEK. THE GFS
HAS A WETTER SOLUTION WITH A WAVE PUSHING THRU THE PLAINS RIDGE
POSITION WHILE THE 00Z ECMWF DOES NOT. WILL STAY WITH THE SUGGESTED
MODEL BLEND AT THIS POINT WHICH DOES KEEP PRECIP CHANCES GOING. BUT
THIS FORECAST IS CERTAINLY SUBJECT TO CHANGE.

AK

&&

.AVIATION...
/ISSUED 101 PM CDT FRI APR 17 2015/
FOR 18Z TAFS...

IFR TO MVFR CIGS ARE EXPECTED FOR THE NEXT 6-7 HOURS AS AN AREA OF
SHRA MOVES ACROSS N AL/S MIDDLE TN. THERE IS THE POTENTIAL FOR LOWER
CIGS (LIFR) BTWN 23Z-01Z AT KMSL AS A LARGE AREA OF SHRA GRADUALLY
MOVES ACROSS NW AL. A BREAK TO VFR CIGS IS THEN ANTICIPATED AFTER
00Z-03Z BUT MFVR VIS IS EXPECTED AS A RESULT OF FOG FORMATION BTWN
00Z-13Z. VFR CONDITIONS SHOULD THEN PREVAIL AFTER 13Z.

SL.77

&&

.PRELIMINARY POINT TEMPS/POPS...
HUNTSVILLE    60  76  66  78 /  20  30 100  90
SHOALS        59  77  65  79 /  20  30 100  80
VINEMONT      59  76  65  78 /  20  40 100  90
FAYETTEVILLE  58  77  65  77 /  20  30 100  90
ALBERTVILLE   59  77  65  77 /  20  40 100  90
FORT PAYNE    58  78  64  76 /  20  30 100  90

&&

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

$$

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



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