Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 051442
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1042 AM EDT TUE MAY 5 2015

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN ACROSS THE REGION THROUGH THE MIDDLE OF
THE WEEK. A WEAK COLD FRONT IS EXPECTED TO DRIFT DOWN FROM THE NORTH
ON THURSDAY. THE REMAINDER OF THE WEEK AND WEEKEND IS STILL FAIRLY
UNCERTAIN AS LOW PRESSURE REMAINS JUST OFFSHORE.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1040 AM...THE LATEST SATELLITE IMAGES INDICATED ONLY A SMALL
AREA OF CU OVER THE HIGH MTN RIDGES. OTHERWISE...THE FORECAST AREA
REMAINS UNDER SUNNY CONDITIONS. KFFC AND KGSO 12Z SOUNDINGS SHOWED A
WELL DEVELOPED INVERSION AROUND 650 MBS. NAM FORECAST SOUNDINGS
INDICATE THAT THE INVERSION WILL CONTINUE TO CAP THE ENVIRONMENT
ACROSS THE FOOTHILLS...PIEDMONT...AND MTN VALLEYS. HOWEVER...MTN
RIDGES SHOULD SEE COVERAGE BEGIN BETWEEN NOON AND 2 PM. I WILL
UPDATE THE FORECAST TO DELAY POPS AND MAKE MINOR EDITS TO HOURLY
TEMPERATURES AND DEWPOINTS.

AS OF 620 AM EDT TUESDAY...PRETTY CALM MORNING IN STORE FOR THE
REGION AS LIGHT/CALM FLOW PREVAILS UNDER MOSTLY CLEAR SKIES.
TEMPERATURES HAVE COOLED OFF DIURNALLY INTO THE 50S FOR MOST
LOCATIONS...WITH DEWPOINT DEPRESSIONS ON THE ORDER OF 3-5 DEGREES
KEEPING ANY PATCHY FOG AT BAY.  THAT SAID...RECENT OBS DO INDICATE
EARLIER FCST FOG IN THE LITTLE TN RIVER VALLEY HAS DEVELOPED...WITH
SOME ADDITIONAL ISOLATED LIGHT FOG ACROSS PORTION OF THE SC PIEDMONT
WITH LITTLE TO NO EXPANSION EXPECTED.  MADE SLIGHT TWEAKS TO VISB TO
ACCOUNT FOR SUCH.  OTHERWISE CURRENT FCST LOOKS GOOD WITH NO
ADDITIONAL CHANGES NEEDED/MADE.

PREVIOUS DISCUSSION...

AS OF 300 AM EDT TUESDAY...UPPER RIDGE AXIS OVER THE LOWER
MISSISSIPPI RIVER VALLEY IS EXPECTED TO ADVECT EAST THROUGH THE
PERIOD.  SURFACE HIGH PRESSURE CENTERED ABOUT 200 MILES OFF THE NC
COAST WILL CONTINUE ITS SLOW PUSH FURTHER OUT TO SEA ALLOWING FLOW
OVER THE SOUTHEAST TO BACK.  EARLIER LOW/MID LEVEL CIGS HAVE SCT OUT
LEADING TO ONLY PATCHY AREAS OF CLOUDINESS AROUND THE 8-10KFT
LEVEL.  EXPECTING THIS TO PREVAIL THROUGH DAYBREAK...ALLOWING FOR AT
LEAST SOME MINOR RADIATIONAL COOLING.  CURRENT DEWPOINT DEPRESSIONS
ACROSS THE REGION LEAN TOWARDS LITTLE FOG POTENTIAL...EVEN WITH SOME
ADDITIONAL COOLING.  ONLY THE MOST FOG PRONE AREAS OF THE LITTLE TN
RIVER VALLEY ARE LIKELY TO SEE ANY VISIBILITY RESTRICTIONS THROUGH
MID MORNING.

OTHERWISE TUESDAY LOOKS TO BE FAIRLY SIMILAR TO THAT OF MONDAY WITH
HIGH PRESSURE PREVAILING.  THAT SAID...LOW LEVEL WAA REGIME
CONTINUES TO YIELD INCREASING DEWPOINTS INTO THE REGION WHICH
COMBINED WITH DIURNAL HEATING WILL PRODUCE MODEST SBCAPE PER LATEST
NAM SOUNDINGS.  FORTUNATELY THE APPROACH OF THE ABOVE MENTIONED H5
RIDGE AXIS WILL LIKELY PROVIDE ENOUGH SUBSIDENCE TO ONCE AGAIN KEEP
WIDESPREAD CONVECTION AT BAY.  THUS...THE FCST FEATURES
ISOLATED/SCATTERED SHRA AND OR TSRA OVER THE NC/GA MTNS...WHILE THE
FOOTHILLS AND PIEDMONT REGIONS REMAIN DRY.  ALL POPS ARE REMOVED BY
MIDNIGHT WITH PARTLY CLOUDY SKIES PREVAILING REGIONWIDE.
TEMPERATURES ON TUESDAY WILL TOP OUT NEARLY 4-5 DEGREES ABOVE NORMAL
FOR MOST AREAS.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
AS OF 230 PM TUESDAY...WE REMAIN KEENLY INTERESTED IN THE NON-
TROPICAL LOW PRESSURE CENTER SHOWN BY THE MODELS OFF THE SOUTHEAST
COAST ON WEDNESDAY AND THURSDAY. RUN-TO-RUN CONSISTENCY CONTINUES TO
BE AN ISSUE WITH THE MODEL GUIDANCE...WHICH THROWS A BLANKET OF
UNCERTAINTY OVER THE FCST. THE LATEST RUNS HAVE TRENDED TOWARD
KEEPING THE LOW FARTHER OFFSHORE...SO MUCH THAT THE WESTERN
CAROLINAS AND NE GEORGIA BARELY FEEL ANY AFFECT FROM THE LOW AT
ALL...AND NOT UNTIL MAYBE EARLY FRIDAY MORNING. INSTEAD...THE SHORT
RANGE WILL CONTINUE TO BE CONTROLLED BY UPPER RIDGING AND A WEAK
SURFACE HIGH...AND A LACK OF FORCING. THAT LEAVES US WITH ONLY SOME
DIFFERENTIAL HEATING OVER THE HIGHER TERRAIN TO ACT UPON THE MINIMAL
LOW LEVEL MOISTURE TO FORM SCATTERED SHOWERS AND A FEW STORMS ACROSS
THE MOUNTAINS IN THE AFTERNOON AND EARLY EVENING WEDNESDAY AND
THURSDAY. WE WILL PROBABLY SEE THE BETTER CHANCE ON THURSDAY WHEN
SOME MOISTURE TO THE NORTH MAY GET ENTRAINED INTO THE DEVELOPING
CIRCULATION OFF THE SC COAST. ONCE AGAIN...CONFIDENCE IN THE
DEVELOPMENT OF SHOWERS DOES NOT SEEM EVEN AS HIGH AS THE 30 PCT
SHOWN IN THE FCST. TEMPS WILL BE A BIT ABOVE NORMAL...AND THE FCST
WAS NUDGED UPWARD A BIT.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
AS OF 315 AM TUESDAY...AS WITH THE SHORT RANGE...THE MEDIUM RANGE
WILL BE SOMEWHAT PLAGUED BY THE UNCERTAINTY WITH THE STRENGTH/
POSITION/TRACK OF A LOW PRESSURE CENTER...WHICH MAY ACQUIRE SUB-
TROPICAL CHARACTERISTICS BY THE END OF THE WEEK. THE NEWEST ECMWF
KEEPS THIS LOW FAR ENOUGH OFFSHORE SUCH THAT THE WESTERN CAROLINAS
ARE SPARED FROM ANY AFFECTS...BUT THE GFS STILL DRIFTS THE LOW WWD
INTO ERN GA OVER THE WEEKEND WHICH COULD BRING AN EASTERLY FLOW THAT
WOULD DRIVE CONVECTION IN FROM THE ATLANTIC. FOR THIS PACKAGE...WILL
BACK OFF WITH THE PRECIP CHANCES ON FRIDAY GIVEN THE DRY ECMWF AND
THE GFS TREND OF KEEPING THE LOW OFFSHORE THRU FRIDAY NIGHT/
SATURDAY MORNING. THAT WOULD LEAVE US WITH YET ANOTHER WEAKLY FORCED
DIURNAL MOUNTAIN SHOWER/T-STORM CHANCE ON FRIDAY AFTERNOON/EVE. NO
CHANGES WERE MADE BEYOND EARLY SATURDAY MORNING. TEMPS WILL REMAIN
SEASONALLY WARM EACH DAY. EVENTUALLY...A SURFACE FRONT MAY DRIFT IN
FROM THE WEST EARLY NEXT WEEK...BRINGING IN A BETTER PRECIP CHANCE.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
AT KCLT AND ELSEWHERE...VFR CONDITIONS WILL PREVAIL THROUGH THE TAF
PERIOD.  INITIALIZED ALL TAFS EITHER SKC...OR WITH FEW LOW/MID
CLOUDS WHERE APPROPRIATE BASED UPON CURRENT OBS/IR SAT.  STILL
FCSTING DIURNAL CU BY LATE MORNING AS LLV LAPSE RATES STEEPEN.
MODEL RH FIELDS INDICATE ANY SCT/BKN CIGS SHOULD STAY ABOVE 6KFT AT
ALL SITES ASIDE FOR KAVL WHERE THE MOIST LAYER IS A TAD DEEPER.
STILL NO WX IN THE TAFS AS DEEP LAYER RIDGING SHOULD KEEP CONVECTION
AT BAY OUTSIDE OF THE HIGH TERRAIN...WITH ONLY LOW CHANCES OF
SHRA/TSRA OVER THE MTNS.  WINDS THROUGH THE PERIOD WILL REMAIN
SOUTHERLY IN THE 5-8KTS RANGE WITH SOME BACKED SE FLOW POSSIBLE THIS
AFTERNOON.

OUTLOOK...ISOLATED TO SCATTERED DIURNAL MOUNTAIN CONVECTION IS
EXPECTED THROUGH FRIDAY...AS MOIST SOUTHERLY FLOW PERSISTS.  LOW
CLOUDS AND OR FOG RESTRICITONS WILL BE POSSIBLE EACH MORNING WHERE
PRIOR AFTERNOON PRECIPITATION OCCURRED.

CONFIDENCE TABLE...

            14-20Z        20-02Z        02-08Z        08-12Z
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  91%
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%     MED   79%

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...PM
NEAR TERM...NED
SHORT TERM...PM
LONG TERM...PM
AVIATION...CDG


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