Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 180617
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
217 AM EDT THU SEP 18 2014

.SYNOPSIS...
A COOL...WEAK RIDGE OF HIGH PRESSURE WILL PERSIST ACROSS THE
AREA...BEFORE STRENGTHENING ON FRIDAY. THIS PATTERN IS EXPECTED TO
PERSIST THROUGH THE WEEKEND...BEFORE A COLD FRONT CROSSES THE AREA
EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 210 AM...A WIDE ARRAY OF CLOUDS ARE PASSING ACROSS THE CWA
THIS EVENING...INCLUDING PATCHY CIRRUS...PATCHY LOW STRATUS...
STRATOCU...AND AN EXTENSIVE DECK OF MID-LEVEL CLOUDS MOVING OVER
WESTERN AREAS FROM THE TENN VALLEY...WHICH IS ASSOCIATED WITH THE
EXIT REGION OF AN UPPER JET MAX. AS SUCH...THE BALANCE OF THE NIGHT
WILL BE MOSTLY CLOUDY...AND THE VARIOUS AREAS OF CLOUDS SHOULD PUT A
DAMPER ON ANY DENSE FOG CONCERNS EARLY THIS MORNING. OTHERWISE...
CURRENT TRENDS NECESSITATED RAISING MIN TEMPS MORE IN LINE WITH
CLIMATOLOGY.

AS OF 730 PM...A FEW SHOWERS HAVE MANAGED TO DEVELOP OVER THE SRN
MOUNTAINS AND UPPER SAVANNAH BASIN ON ACCOUNT OF INSTABILITY
AFFORDED BY SKY THAT CLEARED EARLY ENOUGH IN THE AFTERNOON AND SOME
WEAK LOW LEVEL CONVERGENCE. WILL EXTEND AND ENLARGE THE PRECIP
CHANCE AREA TO INCLUDE MORE OF NE GEORGIA AND THE WRN UPSTATE. THE
SHOWERS SHOULD DIMINISH BY 02Z OR SO. OTHERWISE...CLOUDS CONTINUE TO
DIMINISH...BUT THAT TREND SHOULD HALT WITH SUNSET AND THEN REVERSE
AS A WEAK UPSLOPE FLOW ACTS ON AVAILABLE LOW LEVEL MOISTURE TO BRING
THE LOW CLOUDS BACK.

PREVIOUS DISCUSSION...

AS OF 235 PM EDT...VISIBLE SATELLITE IMAGERY THIS AFTERNOON IS
SHOWING STEADY EROSION OF THE LOW CLOUD LAYER IN THE WEAK CAD REGION
N OF THE RECENTLY DEPARTED BACKDOOR FRONT. THIS SHOULD CONTINUE AS
VAD WIND PROFILES INDICATE LITTLE RESIDUAL UPGLIDE OVER THE CAD.
HOWEVER...BOUNDARY LAYER MOISTURE IS ALLOWING SOME CUMULUS
REDEVELOPMENT AS SCATTERING OCCURS...AND WEAK PASSING H5 SHORTWAVES
ALOFT COULD TRIGGER SOME ISOLD SHALLOW CONVECTION ALONG THE MOST
UNSTABLE SRN/ERN MTNS AND SE PIEDMONT THROUGH EARLY EVENING. THE
BEST FOCUS OF ANY UPPER FORCING SHOULD BE WITH A 60 TO 70 KT UPPER
JETLET CROSSING THE REGION IN WNW FLOW ALOFT...PLACING THE BEST
UPPER DIVERGENCE OVER THE MIDLANDS AND PIEDMONT EAST OF OUR FORECAST
AREA TOWARD EVENING. OTHERWISE...ANTICIPATE MOSTLY DRY CONDITIONS
WITH LOW CLOUDS AND PATCHY FOG FILLING BACK IN ACROSS THE REGION
OVERNIGHT AS SFC WINDS SLACKEN.

A TRAIN OF ADDITIONAL WEAK SHORTWAVES WILL CONTINUE TO PUSH INTO THE
ERN TROUGH ON THU...BUT AGAIN WITH WEAK TRIGGERING AND LIMITED
MOISTURE. WILL FEATURE LOW END ISOLD POPS FOR THU AFTN AS 850 TO 500
MB LAPSE RATES REMAIN REASONABLY STEEP AT 6.5 DEG C/KM. LOW CLOUDS
SHOULD SCATTER A BIT MORE QUICKLY THU...RESULTING IN MAX TEMPS A
DEGREE OR TWO WARMER IN MOST AREAS...BUT STILL A LITTLE BELOW CLIMO.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
AS OF 245 PM EDT WEDNESDAY...THE SHORT TERM FORECAST PERIOD
INITIALIZES THURSDAY EVENING AMIDST POSSIBLE ONGOING
SHOWER/THUNDERSTORM ACTIVITY WITH POPS STARTING OUT AT SLIGHT CHANCE
LEVELS ALONG THE BLUE RIDGE WITH THE REMAINDER OF THE FORECAST AREA
BEING DRY. POPS WILL TAPER OVERNIGHT...WITH AN INCREASING POP TREND
INTO THE AFTERNOON HOURS ON FRIDAY AS HIGH PRESSURE BEGINS TO WEDGE
FURTHER SOUTH LEADING TO INCREASING UPGLIDE POTENTIAL.
THUS...FORECAST WILL FEATURE REGIONWIDE SLIGHT CHANCE POPS FOR
FRIDAY AFTERNOON BEFORE TAPERING FOR THE OVERNIGHT AS THE WEDGE
EXTENDS FURTHER SOUTH ALONG WITH BEST UPGLIDE POTENTIAL.  FORECAST
WILL REMAIN DRY THROUGH SATURDAY AS HIGH PRESSURE CONTINUES TO
STRENGTHEN WITH COOLER NORTHERLY FLOW PREVAILING.  MEANWHILE...THE
NEXT UPPER TROF WILL BE DIGGING ACROSS THE UPPER MIDWEST WITH A COLD
FRONT DRAPED SOUTHWARD ALONG THE MISSISSIPPI RIVER VALLEY.
TEMPERATURES THROUGH THE SHORT TERM WILL REMAIN SEASONABLY COOLER
LEADING TO BELOW NORMAL LEVELS EACH AFTERNOON.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 310 PM EDT WEDNESDAY...NO SIGNIFICANT CHANGES FOR THE EXTENDED
RANGE PORTION OF THE FORECAST WHICH INITIALIZES SATURDAY EVENING
AMIDST DEEP SURFACE WEDGE AND PREVAILING NORTHERLY FLOW.  FORECAST
WILL REMAIN DRY THROUGH THE OVERNIGHT INTO SUNDAY AFTERNOON BEFORE
GRADUALLY RAMPING UP TO SLIGHT CHANCE LEVELS ACROSS THE WESTERN
ZONES OF THE FORECAST AREA WHERE PREFRONTAL/UPSLOPE SHOWER ACTIVITY
WILL REMAIN A POSSIBILITY.  POPS WILL INCREASE ON MONDAY AS UPPER
TROF AND ASSOCIATED COLD FRONT SWING THROUGH THE SOUTHERN/CENTRAL
APPS.  FORECAST WILL FEATURE CHANCE LEVEL POPS ACROSS THE MOUNTAINS
ALONG AND JUST AHEAD OF THE FRONTAL INTRUSION MONDAY AFTERNOON WITH
ONLY SLIGHT CHANCE POPS HIGHLIGHTED FURTHER EAST.  CONSIDERING
RETURNING SOUTHERLY FLOW ON SUNDAY AS ABOVE MENTIONED WEDGE
RETREATS...ALONG WITH IMPROVED SHEAR ASSOCIATED WITH APPROACHING
UPPER TROF AXIS...DID GO AHEAD AN INCLUDE SLIGHT CHANCE THUNDER
MENTION ON MONDAY AFTERNOON.  BEYOND THAT...A DRY FORECAST WILL
PREVAIL FOR THE REST OF THE EXTENDED RANGE AS ANOTHER HIGH PRESSURE
RIDGE SLIDES BY TO THE NORTH AND EXTENDS SOUTHWARD IN YET ANOTHER
WEDGE CONFIGURATION.  SEASONABLE COOLER TEMPERATURES WILL PREVAIL
THROUGH THE PERIOD.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
AT KCLT...ANOTHER ROUND OF LOW-CONFIDENCE AVIATION FORECASTING EARLY
THIS MORNING...AS LOW LEVEL MOISTURE REMAINS ABUNDANT WITHIN A WEAK
EASTERLY FLOW REGIME. SO FAR...MVFR CONDITIONS HAVE DEVELOPED...
WHILE A STUBBORN LIGHT NORTHERLY SURFACE AND PASSING CLOUDS AT
VARIOUS LEVELS ARE PROBABLY THE ONLY THING THAT HAS PREVENTED IFR
CONDITIONS FROM DEVELOPING SO FAR. UNFORTUNATELY...SIMILAR
SUBTLETIES ARE GOING TO DICTATE THE NATURE OF FLT CONDITIONS THROUGH
THE REMAINDER OF THE MORNING. BASED UPON TRENDS IN OBSERVATIONS AND
GUIDANCE...FEEL THAT CHANCES ARE RELATIVELY HIGH THAT OCCURRENCE OF
PERIODIC IFR VISBY WILL INCREASE AFTER 08Z...WHILE LIGHT EASTERLY
FLOW IS EXPECTED TO BRING IFR CIGS INTO THE AREA BY 10Z. CONDITIONS
SHOULD IMPROVE QUICKLY DURING MID/LATE MORNING...WITH VFR EXPECTED
BY NOON. LIGHT N/NE WINDS SHOULD PERSIST THROUGH THE PERIOD.

ELSEWHERE...LIFR CIGS HAVE ALREADY DEVELOPED THIS MORNING AT KAVL.
HOWEVER...THERE IS AN EXTENSIVE AREA OF MID-LEVEL CLOUDS RAPIDLY
ENCROACHING THE AREA FROM THE WEST...AND IT/S NOT OUT OF THE
QUESTION THAT THIS COULD RESULT IN IMPROVEMENT OF CONDITIONS...OR AT
LEAST MAKE CIGS MORE VRBL BY 08Z OR SO. NEVERTHELESS...THE BALANCE
OF THE NIGHT WILL SEE NO BETTER THAN IFR CONDITIONS. THE OTHER
TERMINALS WILL BE MUCH MORE PROBLEMATIC...AS WHETHER OR NOT SUB-MVFR
FLT CONDITIONS WILL DEVELOP IS HIGHLY DEPENDENT UPON THE PERSISTENCE
OF MVFR/VFR CLOUD LAYERS. FOR INSTANCE...KHKY APPEARED ON TRACK FOR
A NIGHT OF SOLID IFR/LIFR CONDITIONS...BUT AN AREA OF MVFR STRATUS
DEVELOPED QUICKLY DURING THE LAST HOUR...MAKING THIS FAR LESS
CERTAIN. THE OTHER TERMINALS GET A TEMPO FOR IFR AROUND DAYBREAK...
BUT AGAIN THIS IS FAR FROM A DONE DEAL AT THIS POINT. CONDITIONS
SHOULD IMPROVE QUICKLY DURING MID/LATE MORNING...WITH VFR EXPECTED
BY NOON. A FEW SHOWERS WILL BE POSSIBLE NEAR THE BLUE RIDGE LATER
TODAY...BUT CHANCES AREN/T HIGH ENOUGH TO WARRANT A TAF INCLUSION
ATTM.

OUTLOOK...THE POTENTIAL FOR LATE NIGHT/MORNING FOG/STRATUS WILL
PERSIST INTO THE EARLY PART OF THE WEEKEND...ESPECIALLY IN THE MTN
VALLEYS. CONDITIONS MAY FINALLY DRY OUT FOR THE LATTER PART OF THE
WEEKEND. A COLD FRONT MAY BRING INCREASING CHANCES FOR SHOWERS/TSTMS
EARLY NEXT WEEK.

CONFIDENCE TABLE...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       MED   75%     MED   77%     HIGH 100%     HIGH  94%
KGSP       HIGH  85%     MED   69%     HIGH 100%     MED   72%
KAVL       MED   64%     HIGH  89%     HIGH 100%     MED   66%
KHKY       HIGH  80%     HIGH  84%     HIGH 100%     MED   64%
KGMU       MED   73%     HIGH  80%     HIGH 100%     MED   72%
KAND       MED   74%     HIGH  87%     HIGH 100%     MED   72%

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...DEO
NEAR TERM...HG/JDL/PM
SHORT TERM...CDG
LONG TERM...CDG
AVIATION...JDL






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