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332
FXUS64 KHUN 011131 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
631 AM CDT MON SEP 1 2014

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 308 AM CDT MON SEP 1 2014/

SYNOPSIS...

THE UPPER FLOW PATTERN ACROSS CENTRAL NORTH AMERICA IS BEGINNING TO
AMPLIFY WITH A RIDGE BEGINNING TO BUILD OVER THE SOUTHEAST, WHILE A
BROAD SHORTWAVE TROUGH MOVES ACROSS THE EASTERN PLAINS AND UPPER MID
WEST. THAT PARTICULAR TROUGH IS BRINGING WIDESPREAD SEVERE WEATHER
ACROSS THE CORN BELT REGION. HOWEVER, ACROSS THE TN VALLEY, REMNANTS
OF THE SHEARED TROUGH AXIS HAVE MOVED OFF TO THE NORTHEAST. THIS
FEATURE WAS RESPONSIBLE FOR BRINGING SHOWERS AND THUNDERSTORMS OVER
THE PAST COUPLE OF DAYS. THE HEAT OFFICIALLY RETURNS TODAY AS IT WILL
DEFINITELY BE HOT AND MUGGY BEGINNING TODAY AND EXTENDING THROUGH THE
REST OF THE WEEK.

SL.77


DISCUSSION...

HIGH CLOUD COVER FROM THE REMNANT VORTICITY MOVING OFF TO THE
NORTHEAST WILL SLOWLY MOVE OFF TO THE EAST TODAY. AS A RESULT,
TEMPERATURES SHOULD RISE INTO THE LOW TO MID 90S WITH SOUTHERLY TO
SOUTHEASTERLY SFC FLOW AND WAA IN PLACE FOR LABOR DAY ACTIVITIES
TODAY. A WEAK CONVERGENCE AXIS DOES EXIST THIS AFTERNOON OVER NE AL
AND HAVE ADDED ISOLATED THUNDERSTORMS OVER THAT AREA AND PORTIONS OF
S MIDDLE TN, THIS AFTERNOON. THEN, WITH A CLEARING SKY AND LIGHT
WINDS, RADIATIONAL COOLING WILL LIKELY LEAD TO PATCHY FOG ALONG
RIVERS, LAKES, AND VALLEYS TONIGHT. NOW, THERE IS THE POSSIBILITY
THAT SFC WINDS MAY NOT COMPLETELY DECOUPLE. THUS, THE REASON WHY FOG
HAS NOT BEEN ADDED TO FORECAST FOR THE WHOLE AREA TONIGHT.

BEFORE THE RIDGE COMPLETELY BUILDS OVER THE REGION, A FEW WEAK
EDDIES WITHIN THE PREVAILING WESTERLIES ARE DEPICTED BY THE MED
RANGE MODELS CROSSING THE SOUTHERN PLAINS ON TUESDAY. ONE OF THESE
ARRIVES OVER THE TN VALLEY ON TUESDAY NIGHT INTO WEDNESDAY BRINGING
THE POSSIBILITY OF MORE WIDESPREAD SHOWERS AND THUNDERSTORMS
ESPECIALLY WITH AN ANTECEDENT TROPICAL AIRMASS ACROSS THE REGION.
THERE IS EVIDENCE OF A WEAK SFC BOUNDARY CROSSING W TN/KY THAT LOOKS
TO STALL CLOSE TO THE AREA AND MAY PROVIDE ANOTHER FOCUSING LIFTING
MECHANISM FOR CONVECTIVE ACTIVITY THAT MAY MOVE SOUTHWARD.
INSTABILITY PARAMETERS ARE SHOWING MODEST INSTABILITY PROFILES (I.E.
BTWN 1500-2500 J/KG OF SBCAPES) ACROSS THE TN VALLEY DURING THE
AFTERNOON. HOWEVER, A WEAKLY SHEARED ENVIRONMENT AND LIGHT STEERING
FLOW WILL TRANSLATE TO MORE PULSE-LIKE THUNDERSTORM ACTIVITY WITH
MICROBURSTS AND HEAVY RAINFALL THE PRIMARY THREATS.

THUNDERSTORM ACTIVITY SHOULD END WEDNESDAY NIGHT. LARGE SCALE
RIDGING ACROSS THE EASTERN HALF OF THE COUNTRY SHOULD TRANSLATE TO A
MORE DIURNALLY FOCUSED THUNDERSTORM TREND DURING THE AFTERNOON HOURS
ON THURSDAY AND FRIDAY. LEFT ISOLATED TO SCATTERED THUNDERSTORM
CHANCES IN THE FORECAST THROUGH THAT PERIOD. HOWEVER, IF THE CENTER
OF THE RIDGE AXIS MOVES ATOP THE TN VALLEY IT MAY INHIBIT ANY
THUNDERSTORM ACTIVITY, ESPECIALLY ON FRIDAY. HOWEVER, WILL WAIT UNTIL
LATER FORECAST MODEL RUNS SHOW MORE CONSISTENCY WITH THE MOVEMENT OF
THIS FEATURE.

THE RIDGE THEN SHOWS SIGNS OF WEAKENING AS A POSITIVELY TILTED
LONGWAVE TROUGH BEGINS TO MOVES ACROSS THE PACIFIC NORTHWEST AND
ALBERTA/MANITOBA ON THURSDAY/FRIDAY. RIGHT NOW, THE RIDGE APPEARS TO
DAMPEN AND SHIFT FURTHER SOUTH ACROSS THE DEEP SOUTH ON SATURDAY AND
SUNDAY. THE TROUGH PUSHES A WEAK SFC FRONT SOUTHWARD. HOWEVER, WITH
THE PREVAILING WESTERLIES SHIFTING TO AN ALMOST PARALLEL ORIENTATION
TO THE NE TO WSW ORIENTED FRONT, EXPECTING SLOW FRONTAL MOVEMENT AS
IT APPROACHES THE OH/MS RIVER VALLEY ON SATURDAY/SUNDAY. FOR NOW,
WILL KEEP THE CHC POPS FOR SATURDAY AND SUNDAY, BUT MAY NEED TO MAKE
ADJUSTMENTS IN LATER FORECASTS IF THIS TREND CONTINUES.

SL.77

&&

.AVIATION...
FOR 12Z TAFS...
WITH AN EXCEPTION OF TEMPO MVFR FOG/MIST THIS MORNING AT KMSL...
VFR WEATHER IS OTHERWISE FORECAST TODAY AND THIS EVENING. LIGHT
SE WINDS THIS MORNING WILL BECOME SW 5-10KT FOR THE LATE MORNING
AND AFTERNOON. WINDS SHOULD BECOME LIGHT/VARIABLE AFTER DUSK.
MVFR MIST/FOG HAS BEEN ADDED TO KMSL LATE IN TAF.

RSB

&&

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

$$

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




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