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000
FXUS62 KGSP 231144
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
744 AM EDT THU MAY 23 2013

.SYNOPSIS...
AN APPROACHING UPPER LEVEL TROUGH WILL CONTINUE TO INFLUENCE THE
REGION TODAY. A COLD FRONT MOVES THROUGH THE AREA TONIGHT...BEFORE A
COOLER AND DRIER AIRMASS SETTLES IN FOR THE WEEKEND. THE AIRMASS
MODIFIES THROUGH THE EARLY PART OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
1155 UTC UPDATE...POPS HAVE BEEN INCREASED IN THE NORTHERN NC
MOUNTAINS AND SOUTHEAST OF KCLT PER RADAR TRENDS.

AT 300 AM EST THURSDAY...AN UPPER TROUGH AXIS WILL CROSS THE OH AND
TN VALLEYS TODAY...CROSS THE SOUTHERN APPALACHIANS THIS EVENING...
THEN MOVES SLOWLY OVER THE EASTERN SEABOARD TONIGHT. THE REMAINS OF
A COLD FRONT WILL CONTINUE TO CROSS OUR AREA EARLY TODAY..EXITING
THE AREA TO THE EAST THIS AFTERNOON. A STRONG COLD FRONT WILL
APPROACH FROM THE NW TODAY...REACHING THE MOUNTAINS BY THIS
EVENING...AND CROSSING THE ENTIRE AREA SHORTLY AFTER MIDNIGHT.

THE ATMOSPHERE WILL DESTABILIZE AGAIN TODAY...WITH MODEST WIND
SHEAR...AND SUFFICIENT DRY AIR ALOFT FOR DOWNDRAFT PRODUCTION. MODEL
TIME HEIGHTS SHOW THE BEST LIFT BETWEEN 18 AND 21Z. A VEERING LOW
LEVEL FLOW WILL DRY OUT THE LOWER LEVELS BEFORE LIFT IS MAXIMIZED IN
THE FOOTHILLS...BUT DEEPER MOISTURE WILL REMAIN IN THE PIEDMONT...
WHERE HEAVIER RAINFALL CAN BE EXPECTED. MAXIMUM TEMPERATURES WILL BE
SLIGHTLY ABOVE NORMAL TODAY.

AS THE COLD FRONT CROSSES THE ARE THIS EVENING...WINDS WILL VEER NW.
MODEL TIME HEIGHTS SHOW SOME LOW LEVEL MOISTURE PERSISTING EAST OF
THE BLUE RIDGE...DESPITE A DOWNSLOPE FLOW...AND LIGHT RAINFALL MAY
PERSIST INTO THE EVENING. POST FRONTAL PRECIPITATION WILL BE BEST
AND MOST PROLONGED ALONG THE TN BORDER WITH NC...WHERE A PRONOUNCED
MOIST NW UPSLOPE FLOW WILL SET UP AND LINGER OVERNIGHT. MINIMUM
TEMPERATURES WILL BE NEAR NORMAL.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 210 AM THURSDAY...AXIS OF AN UPPER TROF SWINGS ACROSS THE AREA
FRI. AT THE SFC...PRESSURE GRADIENT TIGHTENS ACROSS THE AREA AS A
COLD FRONT SLOWLY MOVES EAST AND HIGH PRESSURE SLOWLY MOVES IN FROM
THE WEST. LOW LEVEL MOISTURE LINGERS OVER THE MTNS DURING THE
MORNING...KEEPING SOME SCT RAIN SHOWERS THERE IN THE NWLY UPSLOPE
FLOW. THE SHRA DISSIPATE BY AFTERNOON AS THE MOISTURE DIMINISHES.
THE WIND AND COOLER AIR MASS WILL BE THE BIGGER STORIES. MODERATELY
STRONG LOW LEVEL WINDS MOVE IN AND MIXING SHUD BE ABLE TO TAP THOSE
WINDS DURING THE DAY. ALTHOUGH A WINDY DAY IS EXPECTED...GUSTS SHUD
REMAIN BELOW WIND ADV LEVELS. WITH THE COOLER AIR MASS MOVING IN...
HIGHS WILL BE 5 TO 10 DEGREES BELOW NORMAL.

HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE ARE FRI NITE AS NWLY
FLOW DEVELOPS ALOFT. THE GUSTY WINDS SHUD COME TO AN END DURING THE
EVENING. HOWEVER...THE COLD AIR MASS WILL DROP LOWS TO AROUND 15
DEGREES BELOW NORMAL. IN FACT...TEMPS IN THE NC MTN VALLEYS WILL BE
COLD ENUF FOR FROST. IF THE WIND CAN DIMINISH ENUF...WHICH LOOKS
QUITE POSSIBLE FOR THE SWRN VALLEYS...THEN A FROST ADV WOULD BE
NEEDED.

NWLY FLOW ALOFT REMAINS OVER THE AREA SAT AND SAT NITE AS A FEW WEAK
SHORT WAVES MOVE THRU. AT THE SFC...A WEAK BACK DOOR COLD FRONT
DROPS INTO THE AREA LATE SAT OR SAT NITE. ALTHOUGH MOISTURE
INCREASES SIGNIFICANTLY AND THERE IS SOME FORCING...THE FCST REMAINS
DRY. HIGHS REMAIN NEARLY STEADY OUTSIDE OF THE MTNS...BUT REBOUND A
FEW DEGREES OVER THE MTNS SAT. LOWS SAT NITE ALSO INCREASE...BUT
REMAIN ABOUT 10 DEGREES BELOW NORMAL.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 345 AM THURSDAY...THE GFS AND ECMWF ARE IN GENERAL AGREEMENT
ON THE OVERALL PATTERN DURING THE MEDIUM RANGE. HOWEVER...THERE ARE
SOME SIGNIFICANT DETAIL DIFFERENCES...ESPECIALLY AT THE SFC. NWLY
FLOW ALOFT STARTS OUT OVER THE AREA BETWEEN AN UPPER LOW OVER NEW
ENGLAND AND A RIDGE OVER THE CENTRAL CONUS. THIS FLOW CONTINUES THRU
MON ON THE GFS UNTIL THE RIDGE MOVES EAST OVER THE AREA ON TUE WITH
THE RIDGE REMAINING IN PLACE THRU WED. ON THE ECMWF...THE RIDGE DOES
NOT MOVE IN UNTIL WED.

AT THE SFC...A BACK DOOR COLD FRONT STARTS OUT OVER THE AREA. THE
ECMWF TAKES THE FRONT SOUTH OF THE AREA SUN...KEEPS IT THERE MON
THEN MOVES IT BACK NORTH INTO THE AREA TUE AND KEEPS IT STATIONARY
WED. THE GFS KEEPS THE FRONT OVER OR JUST NORTH OF THE AREA SUN AND
MON...THEN SLIDES IT NORTHWARD TUE AND EASTWARD WED. THE GFS WOULD
INDICATE MORE OF A DIURNAL CHC OF CONVECTION EACH DAY...WHILE THE
ECMWF SUGGESTS MORE OF A STEADY CHC OF CONVECTION. THE GFS HAS BEEN
PRETTY CONSISTENT WITH ITS FORECAST FROM RUN TO RUN...WHILE THE
ECMWF HAS NOT. THEREFORE...SINCE NATIONAL GUIDANCE IS CLOSER TO THE
GFS...HAVE FOLLOWED THOSE TRENDS AS WELL. HIGHS A LITTLE BELOW NORMAL
SUN RISE TO AROUND 5 DEGREES ABOVE NORMAL BY WED. LOWS A FEW DEGREES
BELOW NORMAL AT THE BEGINNING OF THE PERIOD RISE TO A FEW DEGREES
ABOVE NORMAL BY THE END.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
AT KCLT...MVFR CIG RESTRICTION HAS FINALLY DEVELOPED AND WILL BE
CARRIED INITIALLY. THE LATEST GUIDANCE SUPPORTS VFR...SO THE
RESTRICTION WILL ONLY BE TEMPORARY FOR NOW. SW WINDS WILL APPROACH
10 KNOTS THIS MORNING. ANOTHER ROUND OF CONVECTION WITH POSSIBLE
RESTRICTIONS IS EXPECTED THIS AFTERNOON AS A COLD FRONT MOVES
THROUGH FROM THE W... AND ANOTHER APPROACHES FROM THE NW. CONVECTION
WILL MOVE OFF TO THE EAST BY THIS EVENING....WHILE SW WINDS VEER TO
NW AND BECOME GUSTY. MODEL TIME HEIGHTS SUGGEST THE A LOW VFR CIG
WILL PERSIST INTO THIS EVENING.

ELSEWHERE...RESTRICTIONS WILL END BY MID MORNING AS WINDS COME UP
FROM THE SW IN THE FOOTHILLS AND NW IN THE MOUNTAINS. ADDITIONAL
CONVECTION AND RESTRICTIONS ARE EXPECTED BY MIDDAY BETWEEN A
DEPARTING COLD FRONT...AND ANOTHER STRONGER FRONT ARRIVING FROM THE
NW. WINDS WILL VEER TO THE WEST DURING THE DAY IN THE FOOTHILLS AND
BECOME GUSTY...VEERING FURTHER TO BECOME NW IN THE EVENING.
OVERNIGHT PRECIPITATION WILL BE MAINLY CONFINED TO THE MOUNTAINS
BORDERING TN THIS EVENING IN NW UPSLOPE FLOW.

OUTLOOK...VFR WEATHER FRIDAY AND SATURDAY.

CONFIDENCE TABLE...

            11-17Z        17-23Z        23-05Z        05-11Z
KCLT       HIGH  87%     HIGH  98%     HIGH 100%     HIGH 100%
KGSP       HIGH  87%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  94%     HIGH 100%     HIGH  98%     HIGH  83%
KHKY       HIGH  83%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH  92%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH  92%     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...RWH
NEAR TERM...JAT
SHORT TERM...RWH
LONG TERM...RWH
AVIATION...JAT