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Area Forecast Discussion

837
FXUS64 KHUN 041123
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
623 AM CDT WED MAY 4 2016

.UPDATE...
FOR 12Z TAFS

&&

.DISCUSSION...
/ISSUED 548 AM CDT WED MAY 4 2016/
A HIGHLY-AMPLIFIED LONGWAVE PATTERN FOR EARLY MAY CONTINUES TO UNFOLD
ACROSS MUCH OF NORTH AMERICA THIS MORNING...DRIVEN BY A MID TO
UPPER- LEVEL TROUGH APPROACHING THE PACIFIC COAST AND DOWNSTREAM
RIDGE BUILDING ACROSS THE ROCKIES. THE LONGWAVE TROUGH IN PLACE
ACROSS THE EASTERN CONUS WILL CONTINUE TO DEEPEN TODAY AS A RESULT OF
THIS...PUSHING AN INITIAL SHORTWAVE TROUGH EASTWARD ACROSS THE LOCAL
AREA THIS MORNING WITH LITTLE IMPACT. A STRONGER UPPER LOW --
CURRENTLY DROPPING INTO THE NORTHERN GREAT LAKES REGION -- IS
FORECAST TO CONTINUE SOUTHWARD TODAY, REACHING THE SOUTHERN GREAT
LAKES/OHIO VALLEY BY LATE THIS AFTERNOON.

A STRONG LATE SEASON COLD FRONT ASSOCIATED WITH THIS SYSTEM IS
FORECAST TO PUSH RAPIDLY SOUTHWARD AND SHOULD CLEAR MAJORITY OF THE
FORECAST AREA -- WITH PERHAPS THE EXCEPTION OF FAR SOUTHEASTERN
LOCATIONS -- BY 05/00Z. PRIOR TO ARRIVAL OF THE FRONT...THE
COMBINATION OF MODERATE WEST WINDS AND MOSTLY SUNNY SKIES WILL ALLOW
TEMPERATURES TO ONCE AGAIN CLIMB INTO THE L/M 70S. STRONGER MID-LEVEL
ASCENT AND HEIGHT FALLS WILL BEGIN TO OVERSPREAD THE REGION THIS
AFTERNOON AND FAVORABLY COINCIDE WITH FROPA DURING THE MID/LATE
AFTERNOON TO BRING A ROUND OF SHOWERS/THUNDERSTORMS -- MOST LIKELY IN
THE FORM OF A BROKEN LINE ALONG THE COLD FRONT. ALTHOUGH MLCAPE
VALUES AROUND 500 J/KG WILL LIMIT THE INTENSITY OF STORMS...VERY
STEEP LAPSE RATES IN THE SFC-800 MB LAYER WILL SUPPORT WIND GUSTS OF
30-40 MPH AND SMALL HAIL WITH THE STRONGEST CORES. BASED ON EXPECTED
POSITION OF THE COLD FRONT AT 00Z...A CHANCE POP WAS WARRANTED FOR
THE EARLY EVENING HOURS FOR OUR SOUTHEASTERN COUNTIES. HOWEVER...ANY
CONVECTION LINGERING BEYOND SUNSET SHOULD DIMINISH FAIRLY RAPIDLY AS
THE BOUNDARY LAYER BEGINS TO STABILIZE.

SHORT TERM MODELS ARE IN AGREEMENT THAT THE CENTER OF THE UPPER LOW
WILL DIG SOUTHEASTWARD INTO SE KY/SW VA/NE TN BY 12Z THURSDAY...AND
CONTINUE SOUTHEASTWARD THROUGH THE CAROLINAS DURING THE DAY. GUIDANCE
SUGGESTS THAT A STRONG VORTICITY LOBE WILL ROTATE SOUTH-
SOUTHEASTWARD FROM THE OHIO VALLEY INTO THE CUMBERLAND PLATEAU REGION
ON THURSDAY MORNING...BRINGING ANOTHER EPISODE OF LIGHT SHOWERS TO
LOCATIONS EAST OF I-65. THIS ACTIVITY MAY ALSO BE ENHANCED BY
STRENGTHENING UPSLOPE FLOW...AND WE HAVE INCLUDED SLIGHTLY HIGHER
POPS FOR SOUTHERN TN AND NORTHEAST AL TO REFLECT THIS. OTHERWISE...A
SCATTERED/BROKEN STRATOCU DECK WILL IMPACT MAJORITY OF THE REGION AND
WORK IN CONJUNCTION WITH STRONG LOW-LEVEL COLD ADVECTION TO KEEP
TEMPS IN THE 60S TOMORROW AFTERNOON. IN FACT, RIDGETOPS AND PORTIONS
OF THE PLATEAU IN THE EASTERN CWA MAY NOT EVEN REACH 60 TOMORROW.
STRONG NORTH-NORTHWEST WINDS ARE ANTICIPATED REGION-WIDE...AND A WIND
ADVISORY WILL MOST DEFINITELY BE NEEDED FOR ELEVATIONS ABOVE 1000 FT
WHERE SUSTAINED SPEEDS AROUND 30 MPH AND GUSTS TO 40 MPH WILL OCCUR.
CLEARING SKIES WILL ALLOW TEMPS TO DROP INTO THE MID 40S ONCE AGAIN
FRIDAY MORNING...WITH A LIGHT NORTHWEST WIND PREVENTING FULL
RADIATIONAL COOLING.

A REGIME FEATURING STRONGER MID-LEVEL SUBSIDENCE AND HEIGHT RISES IS
EXPECTED TO BEGIN ON FRIDAY...AS THE UPPER LOW MOVES FURTHER UP THE
MID- ATLANTIC COAST AND A SHORTWAVE RIDGE BEGINS TO SHIFT EASTWARD
ACROSS THE SOUTHERN PLAINS. THIS WILL ALLOW TEMPS TO WARM BACK INTO
THE L/M 70S FRIDAY...WITH NORTHWEST WINDS DIMINISHING THROUGH THE DAY
AS A SURFACE RIDGE BUILDS SOUTHWARD INTO THE LOWER MISSISSIPPI
VALLEY. AS THE CENTER OF THE LOW-LEVEL RIDGE SPREADS EASTWARD ACROSS
THE NORTHERN GULF...WINDS WILL SHIFT TO THE WEST-SOUTHWEST FRIDAY
NIGHT/SATURDAY LEADING TO EVEN WARMER TEMPERATURES. MEANWHILE...AN
INTENSE NORTHERN STREAM TROUGH IS FORECAST TO DIG EAST-SOUTHEASTWARD
ACROSS THE GREAT LAKES AND INTO NEW ENGLAND SATURDAY NIGHT/SUNDAY...
WITH THE SYSTEM`S COLD FRONT SERVING AS A FOCAL POINT FOR CONVECTION
FROM THE OHIO VALLEY INTO THE SOUTHERN APPALACHIANS. IT APPEARS AS
IF EITHER THE WEAKENING FRONT OR CONVECTIVE OUTLFOW MAY MAKE IT AS
FAR SOUTH AS NORTHERN TN ON SUNDAY...AND -- ALTHOUGH NOT NOTED IN THE
CURRENT FORECAST -- A FEW SHOWERS/STORMS ARE NOT OUT OF THE QUESTION
IN OUR TN COUNTIES. A RETURN TO WARMER AND MORE HUMID CONDITIONS ARE
IN STORE EARLY NEXT WORK WEEK...AS SOUTHERLY WINDS INCREASE
DOWNSTREAM FROM A MID-LEVEL TROUGH MOVING EASTWARD FROM THE ROCKIES
INTO THE CENTRAL PLAINS. A LOW CHANCE OF SHOWERS/STORMS HAS BEEN
INTRODUCED BY MONDAY AS SOUTHWEST FLOW ALOFT MAY BRING SEVERAL WEAK
DISTURBANCES ACROSS THE REGION EARLY NEXT WEEK.

70/DD

&&

.AVIATION...
FOR 12Z TAFS...
A COLD FRONT CURRENTLY OVER SOUTHERN ILLINOIS WILL CONTINUE SOUTHWARD
AND ENTER THE TN VALLEY BETWEEN 18-21Z. SHOWERS AND THUNDERSTORMS ARE
EXPECTED ALONG THE FRONT BUT DUE TO THE MORE SCATTERED NATURE OF THE
THUNDERSTORMS HAVE OPTED TO GO WITH A VCTS AT BOTH TERMINALS. WINDS
AHEAD OF AND IMMEDIATELY BEHIND THE FRONT WILL BE BREEZY WITH GUSTS
UPWARDS OF 25KTS. AFTER 06Z TONIGHT SURFACE WINDS DROP BELOW 10KTS
BUT SPEEDS AROUND 2000FT ARE EXPECTED TO BE CLOSE TO 30KTS AND LLWS
MAY NEED TO BE INCLUDED IN LATER ISSUANCE`S. VFR CONDITIONS ARE
EXPECTED FOR A MAJORITY OF THE TAF PACKAGE BUT A BRIEF DROP TO MVFR
IS POSSIBLE NEAR THUNDERSTORMS.

STUMPF

&&

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

$$

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



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