Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 230513
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
113 AM EDT THU APR 23 2015

.SYNOPSIS...
A COLD FRONT MOVES SOUTH OF OUR AREA TONIGHT AND COOL...DRY HIGH
PRESSURE BUILDS IN FROM THE NORTH ON FRIDAY.  A WARM FRONT BRINGS
BETTER CHANCES FOR RAINFALL TO OUR REGION OVER THE WEEKEND. DRY HIGH
PRESSURE PREVAILS AT THE START OF NEXT WEEK...THEN A LOW MOVING
ALONG THE GULF COAST INFLUENCES OUR WEATHER IN MID WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 100 AM...UPDATED THE POPS TO MATCH UP WITH A WEAKENING CLUSTER
OF SHWRS AS IT CROSSES THE UPSTATE. THE PRECIP SHUD END OR EXIT TO
THE EAST WITHIN THE NEXT HOUR OR SO. ALSO UPDATED THE SKY AND WIND
GRIDS FOR THE 06Z TAFS.

AS OF 1030 PM EDT WEDNESDAY...EXPECTING LINE OF CONVECTION SLIDING
OUT OF NORTHEAST GA TO MOVE UP THE I85 CORRIDOR AS IT WEAKENS.
LATEST GUIDANCE FAVORS SURVIVAL OF SAID SHRA/TSRA AT LEAST THROUGH
THE I26 CORRIDOR...WITH SOME WEAKENING PROGGED FURTHER EAST.  02Z
SPC MESO ANALYSIS INDICATES LITTLE INSTABILITY TO FUEL THE LINE AS IT
MOVES EAST THUS EXPECTING THUNDER CHANCES TO DIMINISH LEAVING
NOTHING MORE THAN A BAND OF SHRA WITHIN AN HOUR OR SO.
NEVERTHELESS...MODEST LLV WINDS COULD MIX TO THE SURFACE TO PRODUCE
ISOLATED GUSTS OF UP TO 30-40MPH INITIALLY.  MEANWHILE...THE COLD
FRONT IS PUSHING THROUGH THE HIGH TERRAIN ATM...AND SHOULD SWEEP
THROUGH THE REMAINDER OF THE FCST AREA WITHIN THE NEXT FEW HOURS AS
PREVIOUSLY FCST.  TWEAKED POPS/QPF IN THE EXTREME NEAR TERM TO
BETTER REFLECT MOST RECENT RADAR TRENDS.  NO OTHER SIG CHANGES
NEEDED/MADE TO THE FCST WITH THIS UPDATE.

PREVIOUS DISCUSSION...

AS OF 2 PM WED...LATEST VISIBLE SAT IMAGE SHOWS SCT CUMULUS
DEVELOPING OUTSIDE THE MOUNTAINS...WITH CONSIDERABLE CLOUDINESS OVER
THE MOUNTAINS AS A COLD FRONT APPROACHES FROM THE NW. REGIONAL RADAR
SHOWS A FEW LIGHT RETURNS OVER THE MOUNTAINS. CAM MODELS STILL
INDICATE THAT CT SHOWERS WILL DEVELOP MAINLY OVER THE BORDER
COUNTIES OF WESTERN NC CIRCA 20Z AND MOVE SE. ISOLATED THUNDERSTORMS
REMAIN POSSIBLE AS SEVERAL HUNDRED JOULES OF CAPE POOL AHEAD OF THE
FRONT. AIRMASS IS QUITE DRY AND WITH A DEEP LAYER WESTERLY COMPONENT
THROUGH THE COLUMN EXPECT THAT DOWNSLOPE SHOULD ESSENTIALLY KILL
MOST...IF NOT ALL OF THE SHOWERS AS THEY TRY TO MOVE OUT OF THE
MOUNTAINS THIS EVENING. HENCE...MOST AREAS EAST OF THE MOUNTAINS
WILL JUST SEE AN INCREASE IN CLOUDS AND SCT SPRINKLES AT BEST.
GRADIENT WINDS WILL REMAIN STRONG WITH SOME GUSTS TO AROUND 30
MPH...EXCEPT 40-50 MPH IN THE NORTHERN MOUNTAINS. HENCE...WILL
CONTINUE THE WIND ADVISORY IN THE NORTHERN MOUNTAINS. A FEW HIGHER
WIND GUSTS MAY OCCUR WHERE SHOWERS MIX DOWN HIGHER WINDS.

COLD ADVECTION BEHIND THE FRONT WILL BE NOTICEABLE OVER THE MOUNTAINS
TONIGHT. TEMPERATURES ARE FORECAST TO FALL INTO THE MIDDLE 30S TO
LOWER 40S. CLOUDS AND WINDS SHOULD PRECLUDE ANY FROST FORMATION
OVERNIGHT. MINIMUM TEMPS OUTSIDE THE MOUNTAINS WILL RANGE FROM THE
MIDDLE 40S OVER THE NORTHERN FOOTHILLS TO THE MIDDLE 50S IN THE
LOWER PIEDMONT.

THE FRONT WILL MOVE ACROSS THE ENTIRE AREA BY EARLY THU. HIGH
PRESSURE WILL THEN RIDGE SE OVER THE AREA ON THURSDAY. A FEW CLOUDS
MAY LINGER ESPECIALLY OVER SOUTHERN SECTIONS EARLY TOMORROW...BUT
CONSIDERABLE SUNSHINE SHOULD BE THE RULE. MAX TEMPS WILL BE WELL
BELOW CLIMO IN THE MOUNTAINS AND A CATEGORY OR SO BELOW NORMAL
OUTSIDE THE MOUNTAINS.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
AS OF 200 PM WED...UPPER TROUGH AXIS MOVES EWD AND OFFSHORE THU
NIGHT AND FRI ALLOWING HEIGHTS TO RISE OVER THE CWFA...AND DRY HIGH
PRESSURE TO CENTER OVER THE SRN APPALACHIANS BY FRI MRNG. THE
AIRMASS IS CANADIAN IN ORIGIN THOUGH IS LIKELY HAVE MODIFIED TO SOME
EXTENT BY THE TIME IT SETTLES IN. THE SFC HIGH IS NOT THAT
EXPANSIVE...AND FURTHERMORE THE RELATIVELY TIGHT HEIGHT GRADIENT
ALOFT MAY KEEP THE HIGHER ELEVATIONS UNDER SLIGHT FLOW THRU THE
NIGHT. MOS GUIDANCE BASICALLY SUPPORTS A HARD FREEZE OVER THE NRN
MTN ZONES AND VICINITY. THIS SEEMS A BIT TOO LOW. FOR NOW WILL
FEATURE MINS WITHIN A DEGREE OR TWO OF FREEZING AT THE COOLEST
SPOTS. HIGH VALLEYS MAY END UP THE COLDEST. FROST APPEARS TO BE OF
LITTLE CONCERN DUE TO DRY DEWPOINTS THAT WILL ACCOMPANY THE AIRMASS.
CAN/T RULE OUT THE EVENTUAL ISSUANCE OF A FREEZE WARNING...BUT FOR
NOW WILL JUST CONTINUE MENTION IN HWO.

THE HIGH SHIFTS OFF TO THE SOUTHEAST AS THE RIDGE AXIS APPROACHES
LATER FRIDAY. SKIES WILL INITIALLY BE MOSTLY CLEAR AND TEMPS SHOULD
BE ABLE TO REBOUND TO ABOUT A CATEGORY BELOW NORMAL FOR MAXES.
HOWEVER...A SHORTWAVE MOVING FROM THE SRN ROCKIES INTO THE PLAINS AND
ASSOCIATED SFC LOW WILL ADVECT GULF MOISTURE INTO THE SERN STATES.
CLOUDS WILL INCREASE AS ISENTROPIC LIFT RAMPS UP OVER THE AREA DURING
THE SECOND HALF OF THE DAY...WITH POPS FOLLOWING SUIT. CLOUDY SKIES
FRI NIGHT WILL KEEP TEMPS ABOVE FREEZING. MOISTURE AND DEEP FORCING
PEAK DURING THE DAY SATURDAY...WITH AT LEAST MODEST CONVECTIVE
ENHANCEMENT POSSIBLE. PWAT VALUES ARE PROGGED BY THE GFS TO REACH
NEAR RECORD VALUES OVER AT LEAST THE SRN PORTION OF THE AREA. USED
SREF PLUMES TO GET A FEEL FOR QPF...WITH A FAIRLY WIDE RANGE AND
SPATIAL DISTRIBUTION NOTED BETWEEN DIFFERENT MODELS. LOCALLY HEAVY
RAIN IS OF SOME CONCERN SATURDAY ESP IF CONVECTIVE ELEMENTS GET
INVOLVED. HOWEVER WIND PROFILES WILL LIKELY KEEP CELLS MOVING...AND
SOIL CAPACITY LIKELY WILL HAVE RECOVERED SOMEWHAT FROM THE RECENT
RAINFALL.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 205 PM WEDNESDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
SUNDAY WITH FLATTENING UPPER RIDGING OVER THE SE CONUS AND AN H5
SHORTWAVE MOVING INTO THE FCST AREA FROM THE WEST. AT THE SAME
TIME...A LARGE AND PERSISTENT CLOSED UPPER LOW IS SPINNING AND
REMAINS NEARLY STATIONARY OVER NEW ENGLAND. THE OVERALL AGREEMENT
BETWEEN THE LONG RANGE MODELS WRT TO THE SYNOPTIC PATTERN EVOLUTION
DOES NOT LOOK VERY GOOD AT THIS TIME. THE 00Z ECMWF HAS THE H5
SHORTWAVE BEING ABSORBED BACK INTO THE CLOSED LOW LATE SUN AND THE
CENTER OF THE LOW SLIDING GRADUALLY SW ON MON AND TUES. THE GFS
KEEPS THE UPPER LOW FARTHER TO THE NE AND BRINGS ANOTHER ROUND OF
UPPER RIDGING OVER THE FCST AREA ON MON. BOTH MODELS SPIN OFF A
SOUTHERN STREAM CLOSED H5 LOW OVER ARIZONA/NEW MEXICO EARLY IN THE
WEEK AND MOVE THE LOW TO OUR REGION BY MID WEEK. THE GFS MAINTAINS A
DEEPER AND MORE WELL DEFINED LOW COMPARED TO THE ECWMF WHICH TRIES
TO REABSORB THE LOW BACK INTO THE NORTHERN FLOW. REGARDLESS OF THE
SOLUTION YOU USE...BOTH HAVE THE UPPER TROF/LOW MOVING OVER THE CWFA
BY NEW DAY 7 ON WED.

AT THE SFC...A WARM FRONT WILL BE MOVING NORTH OF THE CWFA LATE
SAT/EARLY SUN AS THE PARENT LOW APPROACHES THE CAROLINAS FROM THE
WEST. AS THE CENTER OF THE LOW MOVES TOWARDS THE COAST...LOW LVL
WINDS ARE EXPECTED TO BECOME MORE NORTHERLY AND THE DEEPER LYR
MOISTURE SHOULD DWINDLE. BY MON MORNING...CANADIAN HIGH PRESSURE
WILL SPREAD BACK OVER THE REGION FROM THE NORTH AND DRY THINGS OUT.
ON TUES...A GREAT PLAINS LOW WILL DEEPEN AND MAKES ITS WAY TOWARDS
THE FCST AREA. AT THIS POINT...MODEL DIFFERENCE BECOME MORE
SIGNIFICANT WITH THE ECMWF KEEPING THE LOW ON A MORE SLY PATH AND
NOT HAVING IT REACH THE CWFA UNTIL EARLY WED...WHILE THE GFS
DEVELOPS A DEEPER LOW AND KEEPS IT ON A MORE NLY TRACK AS IT
APPROACHES THE CWFA ON TUES. EITHER WAY...THE END OF THE FCST PERIOD
SHOULD BE THE WETTEST AND MOST ACTIVE. TEMPS START OUT AROUND CLIMO
ON SUN AND STEADILY DROP THRU THE PERIOD WITH HIGHS ON DAYS 6 AND 7
ABOUT 7 TO 10 DEGREES BELOW NORMAL.

&&

.AVIATION /05Z THURSDAY THROUGH MONDAY/...
AT KCLT AND ELSEWHERE...VFR CONDITIONS EXPECTED THRU THE TAF 06Z
TAF PERIOD. A BATCH OF MID LVL CLOUDS WILL EXIT TO THE EAST DURING
THE OVERNIGHT HOURS...WITH JUST FEW-SCT CIRRUS EXPECTED FROM THEN
ON. WINDS WILL SHIFT FROM WEST-SOUTHWEST TO NORTHWEST OUTSIDE THE
MTNS...WHILE THE NW WIND WILL CONTINUE AT KAVL THRU THIS MORNING. A
LEE TROF WILL SET UP THIS AFTN...SHIFTING WINDS BACK TO SW ACRS THE
PIEDMONT SITES. MAY SEE OCCASIONAL LOW-END GUSTS IN THE 15-19 KT
RANGE. AT KAVL...THE NW WIND WILL PICK UP AND SHUD SEE LOW-END
GUSTS. WINDS WILL SUBSIDE THIS EVENING.

OUTLOOK...DRY HIGH PRESSURE WILL BUILD IN ACRS THE REGION THROUGH
FRIDAY...BEFORE ANOTHER WET STORM SYSTEM APPROACHES THE AREA FROM
THE WEST OVER THE WEEKEND ALONG WITH RESTRICTIONS.

CONFIDENCE TABLE...

            05-11Z        11-17Z        17-23Z        23-00Z
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...DEO
NEAR TERM...ARK/CDG/LG
SHORT TERM...WIMBERLEY
LONG TERM...JPT
AVIATION...ARK


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