Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 201954
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
254 PM EST THU NOV 20 2014

.SYNOPSIS...
A COLD FRONT WILL CROSS THE REGION TONIGHT WITH HIGH PRESSURE
BUILDING IN ON FRIDAY AND LINGERING INTO SATURDAY. ABUNDANT MOISTURE
WILL RETURN ON SUNDAY AHEAD OF A LOW PRESSURE SYSTEM LIFTING FROM
TEXAS TO THE GREAT LAKES. THE WEATHER MAY REMAIN UNSETTLED EARLY
NEXT WEEK AS ANOTHER COLD FRONT APPROACHES FROM THE WEST.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 200 PM EST THURSDAY...AN UPPER TROUGH AXIS IS FORECAST TO
SWING ACROSS THE SOUTHEAST THIS EVENING THROUGH TONIGHT AND OFF THE
ATLANTIC COAST BY FRI MORNING. THIS WILL PUSH A TRAILING DRY COLD
FRONT THROUGH THE FORECAST AREA THIS EVENING INTO TONIGHT WITH
SW/WSW WINDS VEERING TO THE NW IN ITS WAKE. CONDITIONS SHOULD REMAIN
DRY WITH CONSIDERABLE LLVL CLOUDINESS CAN BE SEEN ALONG THE TN
BORDER. WITH GOOD NW DOWNSLOPING EFFECT...MORNING LOWS ON FRIDAY
WILL BE A FEW DEGREES WARMER THAN THIS MORNING/S LOW MAINLY EAST OF
THE MTNS.

DURING THE DAY ON FRIDAY...H5 HEIGHTS WILL GRADUALLY RISE OVER THE
REGION AS A WEAK UPPER RIDGE BUILDS IN FROM THE WEST. THIS WILL
ALLOW SURFACE HIGH CENTERED OVER THE OHIO VALLEY TO MIGRATE INTO THE
MID ATLANTIC STATES BY FRI AFTERNOON...SETTING UP A COLD AIR WEDGE
OVER OUR CWA. THEREFORE...WEE WILL SEE CONTINUED DRY CONDITIONS WITH
AFTERNOON TEMPS RUNNING AROUND 7-10 DEGREES BELOW NORMAL.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH MONDAY NIGHT/...
AS OF 145 PM EST THURSDAY...OUR MAIN FOCUS FOR THE SHORT RANGE
PERIOD IS THE SYSTEM EXPECTED TO MOVE THROUGH ON SUNDAY. PRIOR TO
THAT...THE WEATHER SHOULD BE FAIRLY QUIET FOR THE FIRST HALF OF THE
WEEKEND. HEIGHTS WILL BUILD AS AN UPPER RIDGE AXIS CROSSES LATE
SATURDAY. THAT WILL SUPPORT SURFACE HIGH PRESSURE OVER THE MID
ATLANTIC AND CAROLINAS FRIDAY NIGHT THAT SLOWLY DRIFTS OFFSHORE ON
SATURDAY. THEN...THINGS GO QUICKLY DOWNHILL SATURDAY NIGHT.

A STRONG SHORT WAVE IS FCST TO COME OUT ACROSS TX SATURDAY NIGHT TO
AR/MS DELTA REGION BY 12Z SUNDAY. THE PATTERN AMPLIFIES IN RESPONSE
WITH THE FLOW VEERING SW ACROSS THE SOUTHEASTERN UNITED STATES BY
SUNRISE ON SUNDAY. THIS SHOULD OPEN UP THE EASTERN GULF AND ATLANTIC
AND LET MOISTURE RETURN BEGINNING LATE SATURDAY EVENING. A
MOISTENING LOW LEVEL SE FLOW WILL INCREASE SATURDAY EVENING WHICH
SHOULD BEGIN TO FORCE THE DEVELOPMENT OF LIGHT PRECIP NEAR THE SC/NE
GEORGIA BLUE RIDGE BY 06Z. PRECIP CHANCES BEGIN THERE AND GRADUALLY
EXPAND UP THE BLUE RIDGE OVERNIGHT AND OUT OVER THE PIEDMONT AND
FOOTHILLS SUNDAY MORNING...FIRST IN RESPONSE TO THE MECHANICAL LIFT
WITH THE STRENGTHENING SE FLOW...THEN IN RESPONSE TO THE DEVELOPMENT
OF ISENTROPIC LIFT FROM THE S AND UPPER DIVERGENCE FROM THE SW IN
THE 06Z TO 12Z SUNDAY TIME RANGE...AND THE APPROACH OF A VORT MAX
AFTER 12Z. FORTUNATELY...WARM ADVECTION SHOULD KEEP TEMPS ABOVE
FREEZING...SO PRECIP TYPE SHOULD NOT BE AN ISSUE. PRECIP CHANCES
OVERALL LOOK VERY GOOD...SO THE POP WAS ALLOWED TO RAMP UP TO
CATEGORICAL EVERYWHERE BY SUNDAY AFTERNOON. THERE ARE A FEW ISSUES
WITH THIS FCST...CHIEFLY THE SEVERE WEATHER POTENTIAL. AS THE PRECIP
DEVELOPS...THE RETREATING SFC HIGH SHOULD BE IN POSITION TO ALLOW
FOR AN IN SITU COLD AIR DAMMING WEDGE TO DEVELOP IN THE USUAL
LOCATION ON SUNDAY MORNING. ONCE ESTABLISHED... THE WEDGE WILL BE
DIFFICULT TO DISLODGE AND SHOULD PREVENT DESTABILIZATION ACROSS ALL
BUT PERHAPS THE LAKELANDS. THE SHEAR AND HELICITY SHOULD BE VERY
STRONG. THE MAIN SHORT WAVE ACQUIRES A SHARP NEGATIVE TILT AS IT
LIFTS OUT TO OUR WEST ON SUNDAY...WHICH BACKS THE LOW LEVEL FLOW IN
THE AFTERNOON AS THE LOW LEVEL JET TRANSLATES OVERHEAD ATOP THE
WEDGE. AT THIS POINT...THE SITUATION DOES NOT APPEAR FAVORABLE FOR
SEVERE STORMS ACROSS MOST OF THE AREA AS WE WILL HAVE THE HIGH SHEAR
BUT NOT THE LOW CAPE. EVEN THE USUALLY MORE UNSTABLE NAM KEEPS THE
LOW CAPE S OF I-20 THRU 00Z MONDAY. WHATS MORE...WE ALSO LACK THE
STRONG SRN STREAM ADVECTIVE SHORT WAVE THAT WE OFTEN SEE IN EVENTS
THAT RESULT IN SEVERE STORMS DURING HIGH SHEAR LOW CAPE SITUATIONS.
THAT WAVE STAYS WELL TO OUR W AND NW. HEAVY RAIN MIGHT BE THE
GREATER CONCERN...BUT EVEN THAT LOOKS SUSPECT AS THE STRONGER STORMS
MAY LIFT ACROSS THE COASTAL PLAIN... IN THE WARMER AIR AND NEAR THE
WEDGE BOUNDARY...WHICH WILL LIMIT THE MOISTURE TRANSPORT AND PRECIP
RATES ACROSS OUR REGION. FOR NOW...WILL NOT MENTION ANY SEVERE
WEATHER POSSIBILITIES IN THE HWO.

THE MAIN PRECIP SHOULD LIFT OFF TO THE NE SUNDAY EVENING HAVE KEPT
SOME LINGERING PRECIP CHANCE PER THE MODEL GUIDANCE AND NEIGHBORING
FCST OFFICES.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
AS OF 250 PM THURSDAY...ON MONDAY...THE SFC COLD FRONT IS EXPECTED
TO RUN NORTH TO SOUTH ACROSS MIDDLE KENTUCKY AND TENNESSEE BY 12Z
MONDAY. AT H5...THE LONGWAVE TROUGH AXIS WILL AMPLIFY ACROSS THE
CENTRAL CONUS INTO THE SOUTHERN PLAINS. THE PATTERN SHOULD PROVIDE
WARM LLVL TEMPS AND THICKNESSES ACROSS THE FORECAST AREA ON MONDAY.
USING A BLEND OF GUIDANCE...I WILL FORECAST HIGH TEMPERATURES TO
RANGE FROM THE MID 60S WITHIN THE MTN VALLEYS TO THE LOW 70S EAST. I
WILL KEEP A MENTION OF CHC POPS ACROSS THE CWA WITH THE PASSAGE OF
THE COLD FRONT.

TUESDAY...THE LONGWAVE TROUGH WILL APPROACH THE SOUTHEAST THROUGH
THE DAY...RESULTING THE PASSAGE A FEW WEAK VORTS. I WILL KEEP SCHC
TO CHC POPS ACROSS THE REGION. MIN TEMPERATURES SHOULD REMAIN AROUND
5 DEGREES ABOVE NORMAL. HIGH TEMPERATURES ARE FORECAST TO RANGE FROM
THE MID 50S WITHIN THE MTNS VALLEYS TO AROUND 60 EAST. WEAK CAA WILL
DEVELOP ACROSS THE REGION TUESDAY EVENING AND NIGHT. H85 FLOW IS
FORECAST TO REMAIN FROM THE WNW AROUND 20 KTS...SUPPORTING WEAK
NORTHWEST FLOW SHOWERS ALONG THE TN BORDER AND RIDGES. PRECIP IS
EXPECTED TO MIX OVER FROM RAIN TO SNOW DURING THE EVENING...WITH
SNOW REMAIN DURING THE NIGHT. ACCUMS APPEARS TO REMAIN MININMAL
DURING THE PERIOD OF NWFS.

WED THROUGH THURS...THE ECMWF INDICATES THAT DRY ZONAL FLOW WILL
DEVELOP ACROSS THE REGION. THE GFS INDICATES THAT A VERY STRONG MID
LEVEL SHORT WAVE WILL RIPPLE ACROSS THE REGION THANKSGIVING
AFTERNOON...WHICH COULD RESULT IN SIGNIFICANT WEATHER.
HOWEVER...NATIONAL PREFERRED GUIDANCE IS CLOSE TO THE ECMWF...SO IT
WILL BE THE MODEL OF CHOICE. TEMPERATURES WILL REMAIN SLIGHTLY BELOW
NORMAL BOTH DAYS.

&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
AT KCLT AND ELSEWHERE...EXPECT VFR CONDITIONS TO PERSIST THROUGH 18Z
FRI. SW TO WSW WINDS OF 10-15 KTS THIS AFTERNOON WILL DECREASE AND
VEER TO THE NW BY AROUND 6Z AS A DRY COLD FRONT PUSHES THROUGH THE
AREA. THE EXCEPTION WILL BE KAVL WHERE N WINDS SHOULD PREVAIL
THROUGHOUT THE PERIOD. AS SURFACE HIGH PRESSURE BECOMES CENTERED TO
OUR NORTHEAST...N/NW WINDS OVERNIGHT WILL VEER TO THE NE BY TOMORROW
MORNING. SKIES SHOULD REMAIN MOSTLY CLEAR UNDER THE RIDGE OF HIGH
FOR MOST LOCATIONS.

OUTLOOK...DRY HIGH PRESSURE ARRIVES FOR
FRIDAY AND SATURDAY. CLOUDS AND PRECIPITATION RETURN TO THE AREA ON
SUNDAY WITH ANOTHER FRONT...AND ASSOCIATED RESTRICTIONS ARE
POSSIBLE. BRIEF DRYING FOLLOWS THE FRONT ON MONDAY.

CONFIDENCE TABLE...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...CSH
NEAR TERM...JOH
SHORT TERM...PM
LONG TERM...NED
AVIATION...JOH


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