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Area Forecast Discussion

018
FXUS64 KHUN 271125 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
625 AM CDT FRI MAR 27 2015

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 533 AM CDT FRI MAR 27 2015/
A HIGHLY AMPLIFIED MID/UPPER-LEVEL FLOW REGIME PREVAILS ACROSS NORTH
AMERICA THIS MORNING...FEATURING A STRONG RIDGE CENTERED ACROSS
SOUTHERN CALIFORNIA AND A SHARP LONGWAVE TROUGH EXTENDING FROM
EASTERN CANADA INTO THE NW GULF OF MEXICO. THE COLD FRONT WHICH
PUSHED ACROSS THE REGION YESTERDAY EVENING CONTINUES TO MOVE
SOUTHEASTWARD...WITH ALL LINGERING LIGHT RAIN NOW EAST OF THE REGION.
LOW STRATUS CLOUDS HAVE BEEN SLOWER TO DISSIPATE...AND MAY LINGER
WELL INTO THE MID-MORNING HOURS ESPECIALLY FOR AREAS EAST OF I-65. A
STRONG MID-LEVEL VORTICITY MAX -- CURRENTLY DROPPING SOUTH-
SOUTHEASTWARD OVER THE MISSOURI VALLEY -- IS FORECAST TO SPREAD
ACROSS THE LOCAL REGION TODAY. ENHANCED SYNOPTIC SCALE ASCENT
PROVIDED BY THIS FEATURE WILL COMBINE WITH VERY STEEP LOW-LEVEL LAPSE
RATES TO BRING A ROUND OF WIDELY SCATTERED SHOWERS TO THE REGION LATE
THIS AFTERNOON...WITH GREATEST POPS ACROSS THE NORTHWEST WHERE LIFT
MAY BE ENHANCED BY DIFFLUENT FLOW BENEATH THE LEFT EXIT REGION OF AN
UPPER JET MAX ACROSS THE MISSISSIPPI VALLEY. ISOLATED SHOWERS MAY
PERSIST FOR A FEW HOURS AFTER SUNSET...BEFORE COMPLETELY DISSIPATING.
AS THE PARENT DISTURBANCE TRACKS EASTWARD INTO GEORGIA/THE CAROLINAS
THIS EVENING...LINGERING CLOUD COVER WILL ALSO DISSIPATE SETTING THE
STAGE FOR SUB-FREEZING TEMPERATURES...AND FREEZE WARNING HAS BEEN
ISSUED FOR THE ENTIRE REGION. ALTHOUGH LIGHT NORTHERLY FLOW MAY
PREVENT DEVELOPMENT OF A FULLY DECOUPLED PBL /AND LIKEWISE LIMIT THE
THREAT FOR FROST DEVELOPMENT/...DEWPOINTS WILL BE IN THE MID/UPPER
20S AND THIS WILL SUPPORT TEMPERATURES IN THE UPPER 20S/LOWER 30S
ASSUMING EVEN PARTIALLY CLEAR SKIES.

ANOTHER MID-LEVEL SHORTWAVE TROUGH -- FORECAST TO DIG SOUTHEASTWARD
ACROSS MN/IA/MO TONIGHT -- WILL IMPACT WEATHER CONDITIONS ON
SATURDAY. HOWEVER...THIS SYSTEM APPEARS TO WEAKEN CONSIDERABLY AS IT
APPROACHES THE TENNESSEE VALLEY...WITH THE STRONGEST FORCING FOR
ASCENT LIKELY PASSING BY TO THE NORTH/EAST OF THE FORECAST AREA.
REGARDLESS...NORTHWESTERN PORTIONS OF THE AREA WILL REMAIN
SUFFICIENTLY CLOSE TO EXIT REGION OF UPPER JET TO WARRANT A SLIGHT
CHANCE OF LATE MORNING/AFTERNOON SHOWERS. THICKER MID-LEVEL CLOUDS
AND A COLDER START TO THE MORNING WILL TRANSLATE TO HIGHS ONLY
REACHING THE MID 40S FOR MOST LOCATIONS. CONDITIONS WILL BECOME
FAVORABLE FOR A FREEZE ONCE AGAIN SATURDAY NIGHT/SUNDAY MORNING AS
THE VORT MAX TRACKS EASTWARD ACROSS THE SOUTHERN APPALACHIANS AND
SKIES CLEAR DURING THE EVENING. AS CENTER OF SURFACE RIDGE SETTLES
ACROSS THE CENTRAL APPALACHIANS...THE PRESSURE GRADIENT WILL SUPPORT
LIGHT FLOW DURING THE EVENING AND WITH DEWPOINTS RANGING FROM THE MID
TEENS IN THE NE TO THE LOWER 20S IN THE SW A HARD FREEZE IS CERTAINLY
POSSIBLE. HEIGHT RISES AND SUBSIDENCE ALOFT WILL LEAD TO MUCH WARMER
TEMPERATURES ON SUNDAY...AS SOUTHERLY RETURN FLOW STRENGTHENS.

IN THE EXTENDED FORECAST PERIOD...THE INITIAL FEATURE OF INTEREST
WILL BE A STRONG PACIFIC TROUGH FORECAST TO PUSH INLAND ALONG THE
WA/OR COAST LATE TONIGHT AND WEAKEN AS IT SHIFTS EASTWARD THIS
WEEKEND...REACHING THE SOUTHERN GREAT LAKES BY SUNDAY EVENING.
INTENSE LOW-LEVEL WARM/MOIST ADVECTION AHEAD OF THIS FEATURE WILL
SUPPORT DEVELOPMENT OF WIDESPREAD NOCTURNAL CONVECTION ACROSS THE
REGION LATE SUNDAY NIGHT/MONDAY MORNING...WHICH WILL LIKELY DIMINISH
FROM N-TO-S BY EARLY MONDAY AFTERNOON AS A WEAK COLD FRONT DRIFTS
SOUTHWARD INTO CENTRAL ALABAMA. DESPITE THE NORTHWARD RETURN OF
DEWPOINTS IN THE MID 50S...MUCH OF THE CONVECTION WILL BE ELEVATED
EARLY MONDAY MORNING. HOWEVER...DEEP-LAYER SHEAR OF 40-50 KTS WILL
SUPPORT STORM ORGANIZATION ESPECIALLY GIVEN STRENGTH OF MID-LEVEL
LAPSE RATES...AND STRONG STORMS CAPABLE OF PRODUCING GUSTY WINDS AND
SMALL HAIL WILL CERTAINLY BE POSSIBLE. IF LOW-LEVEL MOISTURE RETURN
IS IN ANY GREATER THAN CURRENTLY FORECAST AND CONVECTION CAN BECOME
SURFACE-BASED THEN THE THREAT FOR SEVERE STORMS WILL ALSO INCREASE. A
COOLER PACIFIC AIRMASS WILL MOVE INTO THE REGION MONDAY NIGHT...BUT
TEMPS ARE NOT EXPECTED TO BE NEARLY AS COLD AS WHAT WE WILL SEE THIS
WEEKEND. THIS WILL BE A BRIEF SHOT OF COOLER AIR...AS SOUTHERLY
RETURN FLOW WILL INCREASE WITH PASSAGE OF A WARM FRONT NEXT TUESDAY
NIGHT/WEDNESDAY MORNING. BASED ON AVAILABILITY OF WARM/MOIST AIR...
WE WILL CARRY SLIGHTLY HIGHER THAN CLIMO VALUES FOR SHOWERS AND
THUNDERSTORMS BEYOND THIS POINT...ALTHOUGH GREATEST FORCING FOR
SIGNIFICANT CONVECTION WILL LIKELY COME AFTER THE END OF THIS
FORECAST PERIOD.

70/DD

&&

.AVIATION...
FOR 12Z TAFS...

MVFR CEILINGS WILL PERSIST AT KHSV FOR THE NEXT HOUR OR SO. THE
CLEARING LINE IS NEARING THE TERMINAL...AND SHOULD REACH THERE BY
13Z. OTHERWISE...VFR CONDITIONS ARE EXPECTED FOR MUCH OF THE FORECAST
PERIOD. A DRY AIR MASS WILL SETTLE INTO THE REGION TODAY...AS A WEAK
UPPER LEVEL DISTURBANCE MOVES SOUTHEASTWARD OVER THE AREA. THIS WILL
RESULT IN MID AND HIGH LEVEL CLOUDS...HOWEVER NO IMPACTS ARE
EXPECTED. NORTHERLY WINDS WILL BECOME LIGHT AND VARIABLE AFTER
SUNSET. NO VISIBILITY RESTRICTIONS ARE ANTICIPATED SATURDAY MORNING
DUE TO THE DRY AIR AT THE SURFACE.

73

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...FREEZE WARNING FROM 1 AM TO 10 AM CDT SATURDAY FOR ALZ001>010-016.

     FREEZE WARNING FROM 11 PM SATURDAY TO 9 AM CDT SUNDAY FOR
     ALZ001>010-016.

TN...FREEZE WARNING FROM 1 AM TO 10 AM CDT SATURDAY FOR TNZ076-096-097.

     FREEZE WARNING FROM 11 PM SATURDAY TO 9 AM CDT SUNDAY FOR TNZ076-
     096-097.

&&

$$

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



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