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Area Forecast Discussion

903
FXUS62 KGSP 220546
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
146 AM EDT FRI MAY 22 2015

.SYNOPSIS...
DRY CANADIAN HIGH PRESSURE WILL BUILD OVER THE CAROLINAS AND
NORTHEAST GEORGIA ON FRIDAY AND REMAIN THROUGH THE HOLIDAY WEEKEND.
SOUTHERLY FLOW MOISTURE AROUND BERMUDA HIGH PRESSURE WILL GRADUALLY
RETURN NEXT WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 140 AM...FCST IS ON TRACK. UPDATED THE SKY COVER WITH THE
LATEST NAM...WHICH CONTINUES TO HAVE A GOOD HANDLE ON LOW LEVEL
MOISTURE. ALSO UPDATED THE WINDS FOR THE 06Z TAFS. OTHERWISE...NO
CHANGES.

AS OF 10 PM...I AM VERY IMPRESSED WITH THE HANDLE THE 18Z NAM12 HAS
ON THE CONVECTION THIS EVENING. A CLUSTER OF SHRA DEVELOPED OVER
CHESTER AND YORK COUNTIES AROUND 0Z...PRECISELY AS THE NAM12
INDICATED. THESE SHOWERS DEVELOPED ALONG A SOUTHWARD DRIFTING
CONVERGENCE LINE...ANALYZED AS A SFC TROF. AS OF 2Z...THIS FEATURE
WAS EASILY SEEN ON THE KGSP RADAR PASSING ACROSS SOUTHERN GREENVILLE
AND NORTHERN LAURENS COUNTIES. WINDS NORTH OF THE TROF HAS VEERED
NNW AND HAS BECOME MARGINALLY GUSTY. IN ADDITION...LIGHT SHRA WERE
BRISKLY TRACKING SE ACROSS MRX FA...EXPECTED TO REACH THE MTNS OVER
THE NEXT HOUR. I WILL UPDATE THE FORECAST TO INCORPORATE THE LATEST
CHANGES AND OBSERVATIONS.

AS OF 8 PM...THE FORECAST REMAINS ON TRACK. I WILL UPDATE TO
INCREASE CLOUD COVER ALONG THE TN LINE FOR TONIGHT. IT APPEARS THAT
THE GREATEST PERIOD OF MOIST UPSLOPE FLOW WILL OCCUR FROM 7Z TO 10Z.

AS OF 630 PM...POST FRONTAL DOWNSLOPE FLOW AND FALLING DEWPOINTS
HAVE RESULTED IN VERY COMFORTABLE CONDITIONS EARLY THIS EVENING. I
WILL UPDATE THE FORECAST TO DROP NEAR TERM POPS TO ZERO...REDUCE SKY
COVER...AND ADJUST TEMPS/DEWPOINTS TO OBS. WINDS MAY REMAIN GUSTY
ACROSS THE WESTERN PORTIONS OF THE UPSTATE AND THE UPPER SAVANNAH
RIVER VALLEY FOR ONE TO TWO MORE HOURS. OTHERWISE...WITDS WILL
REMAIN STEADY AROUND 10 MPH WITHIN A LEE TROUGH.

AS OF 230 PM EDT THURSDAY...DRY SLOTTING BEHIND DEPARTING SURFACE
WAVE/FRONT CONTINUES TO PREVAIL OVER NORTHEAST GA AND THE WESTERN
CAROLINAS YIELDING ABUNDANT INSOLATION AMONGST PARTLY CLOUDY SKIES.
TEMPERATURE TRENDS CONTINUE TO IMPROVE SOMEWHAT...ALBEIT NOT AT AS
AGGRESSIVE AS DAYS PAST WITH MOST SITES HOLDING FIRM IN THE
LOWER/MID 80S.  DRIER AIR CONTINUES TO ADVECT INTO THE REGION BEHIND
THE FRONT...AS HIGH PRESSURE APPROACHES AT THE SURFACE.  ENHANCED
PRESSURE GRADIENT FORCES BETWEEN THESE TWO FEATURES WILL CONTINUE TO
YIELD MODERATE NORTH/NORTHWEST FLOW WITH SOME GUSTING LIKELY...AT
LEAST THROUGH SUNSET...LASTING A BIT LONGER OVER THE HIGH TERRAIN.
SKIES WILL REMAIN PARTLY CLOUDY THROUGH THE REMAINDER OF THE
AFTERNOON INTO LATE EVENING AS LOW LEVEL MOISTURE REMAINS TRAPPED
BENEATH STRENGTHENING MID LEVEL INVERSION AHEAD OF FURTHER DRYING IN
THE BOUNDARY LAYER.  CONTINUED NORTHWEST FLOW WILL PRESENT AT LEAST
A NON ZERO CHANCE FOR UPSTREAM LLV MOISTURE TO LIFT MECHANICALLY
ALONG THE WESTERN SLOPES TONIGHT.  THUS...ISOLATED POPS ARE
INTRODUCED FOR A FEW HOURS BEFORE BEING REMOVED BY EARLY MORNING.
FRIDAY LOOKS TO BE A BEAUTIFUL DAY AS DOWNSLOPING FLOW PREVAILS
AMONGST RISING UPPER HEIGHTS...WHILE SURFACE HIGH PRESSURE BUILDS
OVER THE TN VALLEY.  TEMPERATURES ON FRIDAY WILL BE ON THE ORDER OF
5-8 DEGREES BELOW TODAY ON AVERAGE WITH OVERNIGHT LOWS TONIGHT
FALLING INTO THE LOWER/MID 50S WHICH IS A FEW DEGREES BELOW CLIMO.
AS FOR HIGHS ON FRIDAY...EXPECTING TEMPERATURES TO TOP OUT IN THE
LOWER/MID 70S OVER THE PIEDMONT AND MID 60S OVER THE MTNS...NEARLY 5-
8 DEGREES BELOW CLIMO WITH DEWPOINTS IN THE 40S YIELDING LOWER
HUMIDITY.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
AS OF 130 PM EDT THURSDAY...YOU COULD ASK FOR A MORE QUIET...
NORMAL... AND PICTURE-PERFECT MEMORIAL DAY WEEKEND...BUT YOU
PROBABLY WOULD NOT GET IT. THE MODELS ARE IN GOOD AGREEMENT AS TO
THE UPPER PATTERN THAT SHOULD SEE AN ANTICYCLONE CENTERED OFF THE FL
ATLANTIC COAST SLOWLY BUILD FROM FRIDAY NIGHT THRU SUNDAY. THIS
GRADUALLY AMPLIFIES AN UPPER RIDGE WITH AN AXIS THAT REMAINS W OF
THE APPALACHIANS THRU SUNDAY...AND FINALLY MOVES OVER THE WESTERN
CAROLINAS LATE MONDAY. THIS WILL SUPPORT SPRAWLING SURFACE HIGH
PRESSURE MOVING FROM THE GREAT LAKES FRIDAY EVENING TO THE MID
ATLANTIC COAST LATE SATURDAY...THEN SLOWLY OUT OVER THE WESTERN
ATLANTIC THRU MONDAY EVENING. THE SURFACE HIGH WILL RIDGE WESTWARD
THE WHOLE TIME SUNDAY AND MONDAY WITH THE PLUME OF GULF MOISTURE
REMAINING TO OUR WEST. THE MODELS HAVE NO SURFACE-BASED INSTABILITY
THRU SUNDAY NIGHT SO EXPECT IT TO STAY DRY. THE MOISTURE PLUME
CREEPS CLOSER BY LATE MONDAY...SO THIS FAR OUT WE CANNOT RULE OUT
SOME AFTERNOON SHOWERS OR STORMS MONDAY AFTERNOON WITH SMALL CHANCES
STEADILY INCREASING THE FARTHER W ONE GOES IN THE CAROLINAS AND N
GEORGIA. THE BULK OF THE REGION...ESPECIALLY E OF THE MTNS...IS
EXPECTED TO REMAIN DRY. TEMPERATURES WILL CLIMB INCREMENTALLY THRU
THE PERIOD...NEAR OR SLIGHLY BELOW NORMAL SATURDAY...THEN NEAR OR
SLIGHTLY ABOVE NORMAL SUNDAY...THEN PERHAPS FIVE DEGREES OR SO ABOVE
NORMAL ON MONDAY...MEANING HIGHS IN THE LOWER 80S IN THE MTN VALLEYS
AND MID/UPPER 80S E OF THE MTNS.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
AS OF 230 PM EDT THU...NEXT WEEK LOOKS LIKE THE FIRST WEEK OF
SUMMER...IN THAT THE UPPER PATTERN CONTINUES TO SLOWLY EVOLVE WITH
THE UPPER RIDGE AXIS MOVING OFF THE EAST COAST AND TILTING
POSITIVE...WHICH BRINGS A MOIST SW FLOW ALOFT ACROSS THE REGION FROM
MONDAY NIGHT ONWARD. AT THE SURFACE...THIS WILL SUPPORT HIGH
PRESSURE OVER THE WESTERN ATLANTIC IN BERMUDA-HIGH FASHION. AS A
RESULT...A PLUME OF GULF MOISTURE WILL SHIFT EASTWARD OVER THE
WESTERN CAROLINAS...MEANING WE CAN EXPECT HEAT AND HUMIDITY TYPICAL
OF EARLY SUMMER...WITH A CHANCE OF MAINLY DIURNAL SHOWERS AND
THUNDERSTORMS EACH DAY.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
AT KCLT AND ELSEWHERE...DRY HIGH PRES WILL BUILD INTO THE
REGION...MAKING FOR DIMINISHING WIND AND CLEARING SKIES THIS MORNING
THRU MIDDAY. A FEW CIRRUS THIS AFTN POSSIBLE...WITH LIGHT WINDS
BECOMING VARIABLE.

AT KAVL...MOISTURE WILL CONTINUE TO WORK UP THE VALLEY WITHIN
NORTHWESTERLY FLOW...RESULTING IN PERIODS OF MVFR CIGS. DRIER AIR
WILL EVENTUALLY ARRIVE BY LATE MORNING...WITH JUST A FEW CIRRUS FROM
MIDDAY ONWARD. WINDS ARE GUSTING OUT OF THE NORTH AS USUAL BEHIND
COLD FRONTS...AND GUIDANCE GRADUALLY WEAKENS THE WINDS AND LOSES THE
GUSTS BY LATE MORNING. WINDS BECOME LIGHT BY THIS EVENING.

OUTLOOK...DEEP HIGH PRESSURE WILL SETTLE OVER THE REGION...THEN
SHIFT EAST EARLY NEXT WEEK...ALLOWING MOISTURE TO GRADUALLY RETURN
OUT OF THE SOUTH. CONDITIONS SHOULD REMAIN GENERALLY FAIR THROUGH
THE PERIOD.

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       MED   71%     MED   61%     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...ARK/NED
SHORT TERM...PM
LONG TERM...PM
AVIATION...ARK



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