National Weather Service Weather Forecast Office

Area Forecast Discussion

834
FXUS62 KGSP 220758
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
358 AM EDT WED MAY 22 2013

.SYNOPSIS...
AN APPROACHING UPPER LEVEL TROUGH WILL CONTINUE TO INFLUENCE THE
REGION THROUGH THURSDAY. SOUTHERLY FLOW WILL KEEP THE AREA WARM AND
GENERALLY UNSETTLED WITH STORM CHANCES EACH AFTERNOON. A COOLER AND
DRIER AIRMASS SETTLES IN FOR THE WEEKEND AFTER A COLD FRONT MOVES
THROUGH THURSDAY NIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
AT 300 AM EST WEDNESDAY...AN UPPER TROUGH AXIS WILL SLOWLY CROSS THE
MS RIVER VALLEY TODAY AND TONIGHT. A SHORTWAVE ROUNDING THIS UPPER
TROUGH WILL REACH THE SOUTHERN APPALACHIANS THIS EVENING...CROSSING
OUR AREA OVERNIGHT. A WEAKENING COLD FRONT WILL APPROACH OUR AREA
FROM THE WEST TODAY...PRECEDED BY A BAND OF GULF MOISTURE...WHILE
ATLANTIC MOISTURE MOVES NORTH INTO THE PIEDMONT. THESE MOISTURE BAND
CONVERGE OVER OUR AREA TONIGHT. THE FRONT AND MOISTURE ALONG IT
REACH THE INTERSTATE 77 CORRIDOR BY THURSDAY MORNING. ALTHOUGH
INSTABILITY WILL PEAK DURING THE DAYLIGHT HOURS...WINDS SHEAR WILL
INCREASE THIS EVENING...OPENING A WIDER WINDOW FOR SEVERE WEATHER
POTENTIAL. THE MOISTENING AIR MASS WILL SUPPORT HEAVIER RAINFALL
WITH TIME. STEERING FLOW WILL INITIALLY MOVE CELLS INTO THE BLUE
RIDGE ESCARPMENT...BUT BY THE TIME THE BEST MOISTURE ARRIVES...CELL
MOVEMENT SHOULD BE MORE PARALLEL TO THE HIGHER TERRAIN. THIS WILL
LIMIT PRECIPITATION ACCUMULATION...AND NO LARGE SCALE HYDROLOGICAL
PROBLEMS ARE FORESEEN AT THIS TIME. TEMPERATURES WILL RUN A CATEGORY
OR TWO ABOVE NORMAL IN WARM ADVECTION.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AS OF 255 AM WEDNESDAY...SHORT WAVES MOVING THRU AN UPPER TROF PUSH
THE TROF AXIS TOWARD THU THEN INTO THE AREA THU NITE. AT THE SFC...
A PRE-FRONTAL TROF STARTS THE DAY OVER THE AREA WITH A COLD FRONT TO
OUR WEST. THIS FRONT JUMPS INTO THE TROF BY THE END OF THE DAY AND
MOVES EAST OF THE AREA THU NITE. THIS SETS UP TWO AREAS OF FORCING.
ONE OVER THE ERN CWFA ALONG THE TROF AND OVER THE MTNS AHEAD OF THE
FRONT. NE GA AND MUCH OF THE UPSTATE WILL BE BETWEEN THESE 2 AREAS.
THEREFORE...HAVE PUT THE HIGHEST POP OVER THE AREAS WITH BEST
FORCING...BUT DID KEEP LOW CHC POP OVER NE GA AND THE UPSTATE AS
THERE WILL BE WEAK INSTABILITY IN PLACE. BEST INSTABILITY AND SHEAR
WILL BE EAST OF THE AREA...SO DO NOT EXPECT ANY SIGNIFICANT COVERAGE
OF SVR STORMS. PRECIP CHC DIMINISHES OUTSIDE OF THE MTNS DURING THE
EVENING AS THE FRONT MOVES EAST. HOWEVER...SCT SHRA WILL LINGER OVER
THE NC MTNS IN THE DEVELOPING NW FLOW AND CONTINUED LOW LEVEL
MOISTURE. HIGHS THU AROUND 5 DEGREES ABOVE NORMAL WITH LOWS A COUPLE
OF DEGREES ABOVE NORMAL THU NITE.

THE UPPER TROF AXIS MOVES EAST OF THE AREA FRI WITH NWLY FLOW
REMAINING IN PLACE FRI NITE...WHILE SFC HIGH PRESSURE SLOWLY BUILDS
TOWARD THE AREA. ANY LINGERING NW FLOW SHRA END BY AFTERNOON. THE
BIGGER STORIES WILL BE THE WINDS AND COLD AIR MASS MOVING IN. EXPECT
WINDY CONDITIONS TO DEVELOP AS MIXING TAPS SIGNIFICANT LOW LEVEL
WINDS. THAT SAID...IT LOOKS LIKE WINDS AND GUSTS WILL REMAIN BELOW
WIND ADV LEVELS. HIGHS FRI WILL BE 5 TO 10 DEGREES BELOW NORMAL
WHILE LOWS FRI NITE END UP 10 TO 15 DEGREES BELOW NORMAL. RIGHT NOW
IT LOOKS LIKE WINDS WILL REMAIN TOO STRONG FOR ANY SIGNIFICANT FROST
FORMATION OVER THE NC MTNS. HOWEVER...WILL HAVE TO KEEP AN EYE ON
THIS AS TEMPS APPROACH FROSTY LEVELS.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 355 AM WEDNESDAY...THE GFS AND ECMWF ARE IN GENERAL AGREEMENT
THRU THE MEDIUM RANGE. HOWEVER...THERE ARE SOME DETAIL DIFFERENCES.
NWLY UPPER FLOW REMAINS OVER THE AREA SAT AND SUN AS THE CWFA WILL
BE BETWEEN A TROF TO OUR EAST AND A RIDGE TO OUR WEST. THE FLOW
BECOMES ZONAL FOR MONDAY WITH WEAK RIDGING TUE. ALL THIS TIME...
SERIES OF SHORT WAVES MOVE THRU THE FLOW AND ACROSS THE AREA. AT THE
SFC...HIGH PRESSURE RIDGES IN FROM THE NW...BUT IS SPLIT BY A WEAK
BACK DOOR COLD FRONT. THIS FRONT REMAINS OVER OR NEAR THE AREA MON
AND TUE. PRECIP ACTIVATES ALONG THE FRONT FROM TIME TO TIME AS THE
WAVES MOVE OVER. HOWEVER...THE ECMWF IS MUCH MORE WIDESPREAD WITH
PRECIP THAN THE GFS. FOR NOW...HAVE FOLLOWED NATIONAL GUIDANCE AND
KEEP PRECIP LIMITED TO SLIGHT CHC XCPT ACROSS THE NRN MTNS FROM MON
NITE ON. HIGHS AROUND 5 DEGREES BELOW NORMAL SAT AND SUN...NEAR
NORMAL MON...THEN ABOUT 5 DEGREES ABOVE NORMAL TUE. LOWS 5 TO 10
DEGREES BELOW NORMAL SAT NITE...NEAR NORMAL SUN NITE...THEN A LITTLE
ABOVE NORMAL MON NITE.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...LIFR CIG AND MVFR VSBY WILL LKELY BE AROUDN FOR MUCH OF
THE EARLY MORNING. OTHERWISE A LOW VFR CIG IS EXPECTED FROM MID
MORING UNTIL THIS EVENING...WHEN GUIDANCE WOULD SUGGEST A MID TO
UPPER LEVEL CIG. ONCE AGAIN...MODEL SOUNDINGS SUPPORT ROBUST
CONVECTION... AND MODEL DATA SHOWS MOISTURE MOVING IN FROM THE
SOUTH. A MENTION OF THUNDERSTORMS WILL BE MADE IN THE TAF LATE THIS
AFTERNOON AND EARLY THIS EVENING. SOUTHERLY WINDS WILL APPROACH 10
KNOTS THIS AFTERNOON.

ELSEWHERE...GUIDANCE SUPPORTS MVFR CIGS AT FOOTHILL SITES TOWARD
DAWN...AND MVFR VSBY AT ALL SITES BUT KGSP AND KGMU...WHERE LOW VFR
VSBY IS SUPPORTED. IF KAVL CAN FOG UP TO IFR...A LOW CIG WOULD
PROBABLY FORM. VFR RETURNS BY MID MORNING. ANOTHER AFTERNOON OF
ROBUST CONVECTION IS EXPECTED AS AN UPPER TROUGH APPROACHES...WITH
THE BEST COVERAGE IN THE MOUNTAINS. CONVECTION MAY DIMINISH SOME IN
THE EVENING WITH THE LOSS OF HEATING...BUT NOT ENTIRELY...AS COLD
FRONT ARRIVES FROM THE WEST. SSW WINDS WILL APPROACH 10 KNOTS THIS
AFTERNOON.

OUTLOOK... CEILING AND VISIBILITY RESTRICTIONS IN SCATTERED SHOWERS
AND THUNDERSTORMS AGAIN THURSDAY AFTN/EVE. GENERALLY VFR WEATHER
FRIDAY AND SATURDAY.

CONFIDENCE TABLE...

            08-14Z        14-20Z        20-02Z        02-08Z
KCLT       HIGH  82%     HIGH  97%     HIGH 100%     HIGH 100%
KGSP       HIGH  86%     HIGH  98%     HIGH 100%     HIGH 100%
KAVL       HIGH  83%     HIGH 100%     HIGH  95%     HIGH  82%
KHKY       HIGH  86%     HIGH  93%     HIGH 100%     HIGH  94%
KGMU       MED   79%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH  88%     HIGH  97%     HIGH  96%     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