Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 211736
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
136 PM EDT THU MAY 21 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 TONIGHT/...
AS OF 135 PM EDT THURSDAY...TRIMMED BACK ALL POPS FROM THE I77
CORRIDOR AS THE SURFACE WAVE HAS PUSHED INTO CENTRAL NC.  ALSO
TWEAKED SKY/TEMPS/DEWS TO BETTER REFLECT MOST RECENT OBS.
OTHERWISE...NO SIG CHANGES MADE WITH THIS UPDATE AND A FULL FCST
DISCUSSION WILL FOLLOW WITHIN THE HOUR.

PREVIOUS DISCUSSION...

AS OF 630 AM THU...LOW PRESSURE IS CURRENTLY CENTERED OVER THE SRN
APPALACHIANS...MOVING SLOWLY EWD ALONG A STALLED FRONTAL BOUNDARY.
THE BOUNDARY MARKS THE LEADING EDGE OF A DRY CONTINENTAL AIRMASS
SPRAWLING WEST OF THE MTNS. MUCH COOLER/DRIER AIR HAS ALREADY WORKED
THRU MOST OF TENNESSEE. AS MOISTURE INCREASES ON STRENGTHENING
UPSLOPE FLOW BEHIND THE LOW...THE GOING SHOWER ACTIVITY OVER EAST TN
WILL CONTINUE TO PUSH INTO WRN NC FOR A COUPLE MORE HRS AT LEAST.
THOUGH MOST OF THE PIEDMONT ZONES REMAIN IN THE WARM SECTOR OF THE
LOW...IT LOOKS LIKE THE ADVECTION OF MORE UNSTABLE AIR HAS CEASED.
CAN/T RULE OUT SOME LIGHT CONGESTED SHOWERS THIS MRNG...BUT THUNDER
IS LOOKING LESS LIKELY.

THE LOW WILL SLOWLY DEPART THE AREA OVER THE COURSE OF THE DAY...BUT
POPS WILL DIMINISH EAST OF THE MTNS. SUFFICIENT MOISTURE REMAINS
THERE ON THE UPSLOPE FLOW TO KEEP A POP THRU THIS EVENING. EAST OF
THE MTNS DOWNSLOPING AND DRYING IMPLIES CLEARING SKIES. MAX TEMPS
WILL BE MUCH COOLER IN THE MTNS...REACHING ONLY THE MID 70S IN THE
VALLEYS. THE PIEDMONT WILL REMAIN ABOVE NORMAL...MOSTLY MID
80S...BUT WITH LOWER HUMIDITY. A RATHER TIGHT PRESSURE GRADIENT
REMAINS ACRS THE CWFA INTO TONIGHT. THE ORIENTATION OF THE GRADIENT
AS WELL AS A SUBSIDENCE INVERSION NEAR THE TOP OF THE MTNS SUGGESTS
THAT A GAP WIND MAY HOWL IN MTN VALLEYS...PARTICULARLY THE FRENCH
BROAD...KEEPING ASHEVILLE GUSTY MUCH OF THE NIGHT TONIGHT. THIS
COULD ALSO BRING SOME BRISK GUSTS TO GREENVILLE AND SPARTANBURG AS
WELL. MINS WILL BE SLIGHTLY BELOW NORMAL.

&&

.SHORT TERM /FRIDAY 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 WEDNESDAY/...
AS OF 245 AM EDT THU...THE RIDGE AXIS WILL MIGRATE FURTHER OFFSHORE
EARLY NEXT WEEK...WITH SRLY RETURN FLOW MOISTURE IMPROVING MONDAY
INTO TUESDAY. ANTICIPATE ISOLATED DIURNAL CONVECTIVE CHANCES
INCREASING OVER THE MTNS ON MON AFTN IN UPSLOPE AND WEAK
INSTABILITY. A SLOW AND STEADY UPTICK IN DEWPOINTS...MOISTURE...AND
INSTABILITY WILL OCCUR THROUGH TUE...WITH SCATTERED LATE DAY
SHRA/TSRA COVERAGE POSSIBLE IN THE MOUNTAINS. TEMPERATURES WILL
CONTINUE TO WARM...WITH PIEDMONT MAXES AROUND 90 IN ERN/SE SECTIONS
TUE AFTN.

A SHORTWAVE LIFTING E FROM THE PLAINS WILL SLOWLY START TO BREAK
DOWN THE RIDGE ON WED. THIS WILL ALLOW DEEPER MOISTURE TO MOVE INTO
THE SRN APPALACHIANS AND INCREASE CONVECTION TO MORE SOLID CHANCES.
VERY WARM CONDITIONS WILL CONTINUE THROUGH MID WEEK...WITH MAXES
AROUND 90 IN MANY AREAS EAST OF THE MTNS.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AT KCLT AND ELSEWHERE...VFR THROUGH THE PERIOD WITH THE EXCEPTION OF
MVFR CIGS OVERNIGHT AT KAVL.  INITIALIZED ALL TAFS WITH LOW VFR CU
IN ADDITION TO INCREASED NORTHERLY FLOW WITH GUSTING MENTIONED.
NORTH/NORTHWEST GUSTS WILL PREVAIL THROUGH THE AFTERNOON...BEFORE
DECREASING OVER THE UPSTATE AFTER MIXING SUBSIDES...WHILE REMAINING
ELEVATED THROUGH MIDNIGHT AT KCLT AND THROUGH MID MORNING AT KAVL
WHERE CHANNELING IN THE FRENCH BROAD VALLEY PREVAILS.  MODELS
INDICATE LOW LEVEL MOISTURE REMAINING TRAPPED BENEATH MID LEVEL
INVERSION...THEREFORE OPTED TO CARRY FEW LOW VFR STRATUS AT KCLT AND
THE SC SITES...ALONG WITH MVFR CIGS AT KAVL AFTER MIDNIGHT PER
SOUNDINGS.  THAT SAID...CONFIDENCE IS LOW AND IMPACTS WOULD BE
MINIMAL ESPECIALLY OUTSIDE OF THE HIGH TERRAIN.  OTHERWISE...SKIES WILL
EVENTUALLY SCT BY DAYBREAK WITH DEEP LAYER DRY AIR PREVAILING ON
FRIDAY LEADING SKC UNDER CONTINUED LIGHT/MODERATE NORTHERLY
WINDS.

OUTLOOK...DEEP HIGH PRESSURE WILL SETTLE OVER THE SOUTHEAST LATE
THIS WEEK AND REMAIN THROUGH TUESDAY. CONDITIONS SHOULD REMAIN
GENERALLY FAIR THROUGH THE PERIOD.

CONFIDENCE TABLE...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       LOW   57%     HIGH 100%     HIGH  89%     HIGH  83%
KHKY       HIGH 100%     HIGH 100%     LOW   55%     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...WIMBERLEY
NEAR TERM...CDG/WIMBERLEY
SHORT TERM...PM
LONG TERM...HG
AVIATION...CDG


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