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Area Forecast Discussion

250
FXUS64 KHUN 021601 AAB
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
1101 AM CDT THU OCT 2 2014

.UPDATE...
MINOR ADJUSTMENTS TO CLOUD COVER TRENDS AND DEWPOINTS. ALSO LOWERED
RAIN CHANCES A TAD...MAINLY ACROSS NE ALABAMA FOR THE AFTERNOON.

&&

.DISCUSSION...
SURFACE HIGH PRESSURE CENTERED OVER NEW BRUNSWICK EXTENDED
SOUTHWARD TO THE SE STATES. THIS HAS PLACED THE FORECAST AREA IN
A SOUTHERLY FLOW. WITH DAYTIME HIGHS REACHING THE CRITICAL/
CONVECTIVE LEVEL...CUMULUS WERE FORMING IN FORMERLY CLEAR SKIES.
LATE MORNING TEMPERATURES HAVE RISEN INTO THE LOWER 80S.

THIS AFTERNOON APPARENTLY WILL BE THE LAST VERY WARM TO HOT DAY
ACROSS THE TENNESSEE VALLEY FOR A GOOD WHILE. A STRONG COLD FRONT
NOW TRAVERSING EASTWARD ACROSS THE WESTERN/CENTRAL GREAT PLAINS
WILL APPROACH...AND BRING VERY GOOD CHANCES OF SHOWERS AND
TSTORMS...ESPECIALLY DURING THE OVERNIGHT. SOME OF THE STORMS COULD
BECOME SEVERE...WITH DAMAGING WINDS THE MAIN THREAT. CURRENT RADAR
TRENDS INDICATED CONVECTION HAS FORMED ACROSS WESTERN TENNESSEE
(NORTH OF CORINTH) SOUTHWARD TO THE GOLDEN TRIANGLE. THIS
ACTIVITY...MOVING NNE 15-20 MPH SHOULD BEGIN AFFECTING PARTS OF NW
ALABAMA DURING THE COURSE OF THE LATE MORNING AND EARLY AFTERNOON.
THIS DEVELOPMENT... AND POSSIBLE NEW DEVELOPMENT COULD AFFECT AREAS
AROUND THE I-65 CORRIDOR LATE IN THE AFTERNOON AND EVENING.

THE FORECAST FOR THIS AFTERNOON IS OVERALL IN GOOD SHAPE. MADE
UPDATES TO CLOUD TRENDS...MAINLY CONCERNING CLOUDS ASSOCIATED WITH
THE CONVECTION OUT WEST...AND EXPECTED COVERAGE THIS AFTERNOON.
LOWERED POPS SOMEWHAT...MAINLY FOR AREAS EAST OF I-65 FOR THE
AFTERNOON. TEMPERATURES AND WINDS LOOK GOOD FOR NOW.

RSB

&&

.AVIATION...
/ISSUED 557 AM CDT THU OCT 2 2014/
FOR 12Z TAFS... VFR CONDITIONS ARE EXPECTED THROUGH MOST OF THE
PERIOD. SCT DIURNAL CUMULUS WILL DEVELOP BY LATE MORNING INTO EARLY
AFTERNOON. A FEW SHRA AND POSSIBLY TSRA MAY DEVELOP BY LATE THIS
AFTERNOON. A LINE OF TSRA WILL ARRIVE FROM 07-11Z AT KMSL AND 09-12Z
AT KHSV. THE TSRA WILL PRODUCE A PERIOD OF GUSTY WINDS AND FLIGHT
RESTRICTIONS TO AT LEAST MVFR. +RA MAY YIELD BRIEF IFR CONDITIONS BUT
WILL ADDRESS THAT IN LATER UPDATES AS THE SITUATION BECOMES MORE
CLEAR.

AK

&&

.PREV DISCUSSION...
/ISSUED 313 AM CDT THU OCT 2 2014/

SYNOPSIS...

A DEEPENING UPPER TROUGH OVER THE ROCKIES AND NORTHERN PLAINS IS
BRINGING SEVERE WEATHER ACROSS THE CENTRAL PLAINS AND WILL BE THE
MAIN PLAYER FOR THE WEATHER TONIGHT INTO THIS WEEKEND. THE PRIMARY
IMPACT AND WHAT WILL BE DISCUSSED FURTHER IS THE POTENTIAL FOR
STRONG TO SEVERE WEATHER ACROSS THE TN VALLEY LATE TONIGHT INTO
FRIDAY MORNING. ANOTHER NOTICEABLE IMPACT IS THAT THE CP AIRMASS
BEHIND THE INDUCED SFC LOW/FRONT WILL BRING AN ABRUPT CHANGE TO
SENSIBLE WEATHER. THIS WILL BE ESPECIALLY TRUE ON FRIDAY/SATURDAY
WITH TEMPS BETWEEN 20-25 DEGREES LOWER BY THIS WEEKEND.

SL.77

WARM AIR ADVECTION AHEAD OF THE APPROACHING TROUGH/FRONTAL SYSTEM
WILL CONTINUE IN EARNEST TODAY WITH 5-10 KNOTS OF SFC FLOW WHILE THE
LLJ SLOWLY INCREASES THROUGHOUT THE DAY. WITHIN THE WARM AIR
ADVECTION, EXPECTING CLOUDS AND WEAK SHOWERS/STORMS TO DEVELOP
ACROSS MS AND POSSIBLY MOVE OVER NW AL THIS MORNING EXPANDING EAST
THROUGHOUT THE DAY. THEY WILL BE ISOLATED TO SCATTERED IN NATURE.
DEWPOINTS WILL RISE INTO THE MID TO UPPER 60S BY LATE TONIGHT AS A
RESULT OF THE WARM AIR ADVECTION. AS THE TROUGH APPROACHES, A QLCS
CURRENTLY FORMING/ORGANIZING OVER THE CENTRAL PLAINS TO MO WILL MOVE
EAST OVER THE COURSE OF THE DAY TODAY. THIS LINE WILL APPROACH THE
MS RIVER VALLEY THIS AFTERNOON AND TONIGHT WITH AN ANTECEDENT
UNSTABLE AND AMPLY SHEARED ENVIRONMENT FOR A DAMAGING WIND/SPIN UP
TORNADO THREAT.

AS THIS QLCS MOVES CLOSER TO NORTH MS/NORTHWEST AL, THERE IS STILL A
LITTLE DIFFERENCE IN MODEL GUIDANCE ON THE PREVAILING ENVIRONMENT,
BUT BELIEVE THAT THE S/SW LLJ AND LOCATION OF THE RR QUADRANT OF THE
MID-UPPER LEVEL SOUTHWESTERLY JET STREAKS BTWN 06-10Z WILL TRANSLATE
TO 0-3 KM SRH VALUES OF 200-300 M2/S2 AND BULK SHEAR BTWN 35-45 KTS.
THE WIND SHEAR IS NEARLY UNI-DIRECTIONAL BUT (MUCAPE) INSTABILITY IS
BETWEEN 800-1200 J/KG AS THE QLCS APPROACHES. IT IS NOTED THAT
INSTABILITY AND WIND SHEAR DO DECREASE SOMEWHAT FURTHER EAST, BUT
THE QLCS MAY NOT WEAKEN OR LOSE ORGANIZATION AS IT CROSSES INTO NW
AL. WITH THAT IN MIND, BELIEVE THAT THE HIGHEST THREAT WILL BE OVER
NW AL WITH DAMAGING WINDS AND BRIEF SPIN-UP TORNADOES THE PRIMARY
THREATS WITH ANY BOWING SEGMENTS. HEAVY RAINFALL WILL BE A THREAT BUT
WITH THE ANTECEDENT DRY CONDITIONS, DO NOT BELIEVE WE WILL HAVE MUCH
MORE THAN A NUISANCE FLOODING THREAT WITH THIS LINE. FURTHER EAST
(EAST OF INTERSTATE 65) THE LINE WILL LIKELY START TO LOSE
ORGANIZATION BY 08-12Z OVER NE AL.

THEN, TRAILING STRATIFORM LOOKS TO PREVAIL FOR AT LEAST PART OF THE
DAY ON FRIDAY BEFORE THE PRIMARY CP COLD FRONT APPROACHES ON LATE
FRIDAY MORNING INTO THE AFTERNOON. THERE IS A CHANCE FOR
THUNDERSTORMS AS THE FRONT PASSES WITH DAYTIME HEATING CONTRIBUTING
TO THE ENVIRONMENT BECOMING UNSTABLE. THERE IS SOME UNCERTAINTY ON
THE WIND SHEAR PROFILE AND LAPSE RATES, BUT WITH INVERTED V PROFILES
AND ~30 KTS OF BULK SHEAR, STRONG THUNDERSTORMS ARE POSSIBLE WITH
GUSTY WINDS THE PRIMARY THREAT. SUSTAINED WINDS BTWN 10-20 MPH WILL
BE POSSIBLE AHEAD AND IMMEDIATELY BEHIND THE FRONT

THEN, A COLD POLAR BLAST FOLLOWS WITH TEMPERATURES FALLING INTO THE
MID TO UPPER 40S ON FRIDAY NIGHT WITH A CLEAR SKY. DAYTIME HIGHS ON
SATURDAY WILL THEN STRUGGLE TO REACH INTO THE UPPER 60S. THE LOWEST
TEMPS OF THE SEASON SO FAR WILL BE ON SATURDAY NIGHT AS LIGHT WINDS
AND CLEAR SKY AND DEWPOINTS IN THE 30S YIELD OVERNIGHT LOWS CLOSE
POSSIBLY DIPPING IN THE UPPER 30S OVER HIGHER ELEVATIONS OF THE
CUMBERLAND PLATEAU BY SUNDAY MORNING.

BY SUNDAY, THE UPPER TROUGH THAT BROUGHT THE THUNDERSTORMS AND
STRONG COLD FRONT IS THEN BLOCKED FROM MOVING EAST AND BROADENS--
EXPANDING WESTWARD. THIS WILL PLACE THE SOUTHEAST WITHIN THE UPPER
NW FLOW ALOFT AND A FEW MID-LEVEL SHORTWAVE TROUGHS MOVING WITHIN
THE FLOW. THERE IS THE POSSIBILITY THAT SOME LOW LEVEL SOUTHERLY
FLOW MAY INCREASE SATURATION LEVELS TO YIELD ISOLATED SHOWERS ON
MONDAY (AND POSSIBLY TUESDAY). OTHERWISE, DAYTIME HIGH TEMPS SHOULD
BEGIN TO MODERATE BACK INTO THE 70S AND 80S AS THE AIRMASS IS
MODIFIED OVER THE COURSE OF THE EXTENDED.

SL.77

&&

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

$$

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



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