Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 180745
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
345 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 TONIGHT/...
STRATOCU CONTINUES TO GRADUALLY EXPAND ACROSS EASTERN AREAS...WHILE
A FAIRLY EXTENSIVE AREA OF MID-LEVEL CLOUDS CONTINUES TO ENCROACH
FROM THE WEST. THIS SHOULD CONTINUE TO PRECLUDE ANY DENSE FOG
CONCERNS EARLY THIS MORNING. OTHERWISE...WITH WEAK MID-LEVEL SHORT
WAVE TROUGH AND UPPER JET ENTRANCE REGION PUSHING EAST OF THE AREA
BY LATE MORNING...WE ARE EXPECTING SCATTERING/LIFTING OF CLOUDS TO
OCCUR A BUT QUICKER THAN IT DID YESTERDAY...WHICH SHOULD RESULT IN
TEMPS WARMING TO NEAR 80 IS MOST AREAS OUTSIDE THE MTNS...AND MID
70S IN THE MTN VALLEYS. AS A RESULT...NAM FORECAST SOUNDING CAPE IS
SURPRISINGLY ROBUST...AROUND 2000 J/KG IN THE PIEDMONT. HOWEVER...IT
IS THE ONLY MODEL THAT FEATURES EVEN ANYTHING APPROACHING THIS
DEGREE OF INSTABILITY. IN FACT...THE SREF /LIKELY PROBABILITY/ OF
CAPE > 500 J/KG IS CONFINED TO A RATHER SMALL AREA AROUND THE
SOUTHERN PERIPHERY OF THE CWFA. MEANWHILE...ONCE THE MID-LEVEL WAVE
PASSES BY LATER THIS MORNING WITH LITTLE FANFARE...THERE WON/T BE
MUCH OF A SIGNIFICANT SOURCE OF RISING MOTION. THEREFORE...WHILE
CONVECTION IS POSSIBLE LATER TODAY...THIS IS CERTAINLY SUPPORTED BY
THE LATEST CONVECTION ALLOWING MODELS...IT SHOULD PRIMARILY BE OF
THE SHOWER VARIETY AND ISOLATED IN NATURE.

TONIGHT...SHORT TERM MODELS DEPICT A BIT OF AN INCREASE IN THE LOW
LEVEL EASTERLY FLOW...ALONG WITH A PERSISTENT QPF RESPONSE...ESP
NEAR THE BLUE RIDGE. POPS WILL THEREFORE INCREASE JUST A BIT
TONIGHT...ESP ALONG THE EASTERN ESCARPMENT...BUT CHANCES ARE STILL
EXPECTED TO BE NO BETTER THAN 30 PERCENT. MIN TEMPS WILL AVERAGE
FAIRLY CLOSE TO CLIMO.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 300 AM THU...SPRAWLING CONTINENTAL HIGH PRESSURE INITIALLY
COVERS MUCH OF THE ERN CONUS FRIDAY MORNING...BUT UPPER PATTERN
REMAINS PROGRESSIVE AND THE HIGH STEADILY SHIFTS OFF INTO THE
ATLANTIC DURING THE PERIOD. AIDED BY CONFLUENCE IN THE CO-LOCATED
ENTRANCE REGION OF A SHORTWAVE...THIS HIGH WILL CREATE A SHORT-LIVED
CAD EVENT AGAINST THE SRN APPALACHIANS. EASTERLY FLOW INITIALLY WILL
WARRANT POPS NEAR THE BLUE RIDGE...BUT AS MOISTURE BECOMES MORE
SHALLOW THRU THE DAY THIS BECOMES A LESSER FACTOR. UPGLIDE OVER THE
WEDGE IS UNIMPRESSIVE...APPEARING CAPABLE OF A FAIR AMOUNT OF CLOUD
COVER BUT NOT MEASURABLE PRECIP. HOWEVER NAM/GFS BOTH INDICATE MODEST
INSTABILITY DURING PEAK HEATING...AND FOR THE AFTN HOURS THAT IS THE
MAIN DRIVER FOR POPS. AT LEAST A SCHC IS INCLUDED EVERYWHERE...WITH
CHC OVER MTN RIDGES. THESE POPS SLOWLY DIMINISH FRI NIGHT AS LLVL RH
CONTINUES TO DROP. MAX TEMPS WILL BE ABOUT TWO CATEGORIES BELOW
CLIMO...WITH MINS NEAR CLIMO SAT MRNG.

THOUGH RIDGING IS SEEN DOWN THE ERN SEABOARD ON SATURDAY THE WEDGE IS
LIKELY TO LOSE ITS GRIP ON THE REGION AS THE PARENT HIGH MOVES
FURTHER AWAY. ISENTROPIC LIFT BECOMES ESSENTIALLY NEUTRAL AND
MOISTURE OVER THE WEDGE IS NOT SUFFICIENT TO EXPECT MUCH CLOUD COVER
TO PERSIST THRU THE DAY. RISING HEIGHTS ARE REFLECTED IN WEAKER LAPSE
RATES ON MODEL PROFILES...BUT AS FAR AS IMPACTING INSTABILITY THIS IS
COUNTERACTED BY WARMER SFC TEMPS. NONETHELESS BLENDED GUIDANCE
SUPPORTS A DRY FCST. TEMPS WILL REBOUND SLIGHTLY...TOPPING OUT A
COUPLE DEGREES BELOW CLIMO SAT AFTN. HOWEVER MINS SHOULD BE A LITTLE
BELOW CLIMO SUN MRNG UNDER CLEARER SKIES.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 300 AM THU...DEEP TROUGH WILL DIG INTO THE ERN CONUS SUNDAY AS
THE UPPER PATTERN AMPLIFIES ONCE AGAIN. THIS WILL DRIVE A COLD FRONT
SEWD THRU THE OH/TN VALLEYS SUNDAY...CROSSING THE MTNS SUNDAY NIGHT
AND CLEARING OUR AREA BY LATE MONDAY. 18/00Z GFS AND 18/00Z EC ARE IN
PRETTY GOOD AGREEMENT ON THIS TIMING AND BOTH MODELS SHOW A WELL
DEFINED SHORTWAVE COMING THRU THE AREA WITH THE FRONT...EVEN IF WIND
FIELDS ARE NOT THAT IMPRESSIVE. NEITHER MODEL DEVELOPS THAT MUCH
QPF...WITH THE FRONT INTERCEPTING DEEP DRY AIR OVER THE SOUTHEAST.
ANOTHER LARGE AREA OF DRY CONTINENTAL HIGH PRESSURE ARRIVES IN THE
WAKE OF THE FRONT...WHICH SHIFTS ACRS THE MTNS TUESDAY TO USHER IN
EASTERLY FLOW THROUGH THE END OF THE PERIOD...THOUGH MOISTURE
PROFILES REMAIN SEASONABLY DRY SO NO POPS WILL BE MENTIONED AT THAT
TIME. TEMPS WILL BE AROUND NORMAL SUN-MON...BEFORE DROPPING TO A FEW
DEGREES BELOW NORMAL FOR TUE-WED.

&&

.AVIATION /08Z 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...

            07-13Z        13-19Z        19-01Z        01-07Z
KCLT       MED   70%     HIGH  84%     HIGH 100%     HIGH  94%
KGSP       HIGH  89%     MED   75%     HIGH 100%     MED   68%
KAVL       MED   69%     HIGH  92%     HIGH 100%     MED   63%
KHKY       MED   70%     HIGH  90%     HIGH 100%     MED   67%
KGMU       MED   70%     HIGH  91%     HIGH 100%     MED   68%
KAND       MED   75%     HIGH  92%     HIGH 100%     MED   68%

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...JDL
NEAR TERM...JDL
SHORT TERM...WIMBERLEY
LONG TERM...WIMBERLEY
AVIATION...JDL





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