Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS62 KGSP 170752
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
352 AM EDT WED SEP 17 2014

.SYNOPSIS...
A COOL RIDGE OF HIGH PRESSURE WILL SLOWLY BUILD SOUTHWEST ACROSS THE
AREA THROUGH TONIGHT...THEN INTENSIFY 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/...
A BACKDOOR COLD FRONT CONTINUES TO DROP SLOWLY SOUTH ACROSS THE
FORECAST AREA EARLY THIS MORNING...CURRENTLY DRAPED JUST EAST OF THE
I-85 CORRIDOR. A WEAK SURFACE HIGH WILL CONTINUE TO OOZE INTO THE
MID-ATLANTIC TODAY...AND THESE FEATURES WILL BE THE PRIMARY PLAYERS
IN THE FORECAST LATER TODAY...WHICH CAN BE BEST DESCRIBED AS BEING
OF THE /LOW CONFIDENCE/ VARIETY...WITH SOME SIGNIFICANT BUST
POTENTIAL. WHILE THE SURFACE PATTERN WILL BE /WEDGE-LIKE/ TODAY...
THE SITUATION WILL BE ANYTHING BUT CLASSICAL...AS THE SURFACE HIGH
IS VERY WEAK AND NOT IN VERY GOOD POSITION. IN FACT...SOME OF THE
SHORT TERM MODELS ADVECT DRIER AIR INTO THE NORTHEAST PART OF THE
FORECAST LATER THIS AFTERNOON...WITH THE NAM OFFERING (BY FAR) THE
WETTEST SOLUTION. THE NAM DEVELOPS A WELL DEFINED SOUTHWESTERLY LOW
LEVEL JET ALONG A NARROW AXIS ACROSS THE PIEDMONT LATER TODAY IN
RESPONSE TO SURFACE WAVE DEVELOPMENT ACROSS THE COASTAL PLAIN.
HOWEVER...IT IS CONSIDERABLY STRONGER WITH THIS WAVE AND LLJ THAN
ANY OTHER MODEL.

THE UPSHOT IS THE NAM IS PRODUCING A LOT OF PRECIP OVER THE PIEDMONT
THIS AFTERNOON. BUT IS A BIT OF AN OUTLIER IN THIS REGARD. THE FACT
THAT THE 00Z RUN INDICATED THAT THERE WOULD BE A LOT OF PRECIP GOING
ON RIGHT NOW ACROSS WESTERN NC GIVES THE NAM A BIT OF A CREDIBILITY
PROBLEM FROM THE GET-GO. ALL THINGS CONSIDERED...WE HAVE OPTED TO
FEATURE A FORECAST THAT IS MORE IN-LINE WITH DRIER MODEL
SOLUTIONS...AND GENERALLY FEATURE SLIGHT CHANCE POPS ACROSS THE NC
PIEDMONT...AS WELL AS PORTIONS OF THE MTNS THIS AFTERNOON.

TEMPS WILL ALSO BE PROBLEMATIC. AGAIN...THIS IS NOT A CLASSICAL
WEDGE SCENARIO...AND THE DEGREE OF HEATING (OR LACK THEREOF) TODAY
WILL BE LARGELY A FUNCTION OF THE EXTENT OF LOW CLOUD COVER. THIS IS
COMPLICATED BY THE FACT THAT MODEL SOLUTIONS INDICATE DRY AIR WILL
BE ENCROACHING ON THE AREA FROM MULTIPLE DIRECTIONS (NE AND
SW)..WITH A GUIDANCE CONSENSUS INTRODUCING DRIER AIR INTO THE
WESTERN ZONES LATER TODAY. OUR CURRENT BEST GUESS WAS TO DEPICT
MAXES RANGING FROM AROUND 70 ACROSS THE NORTHWEST NC PIEDMONT...TO
THE LOWER 80S ACROSS THE UPPER SAVANNAH RIVER VALLEY/LOWER SC
PIEDMONT.

CLOUDS SHOULD PERSIST AND/OR REDEVELOP IN MOST AREAS TONIGHT...WITH
MIN TEMPS EXPECTED TO COOL TO NEAR CLIMO.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
AS OF 300 AM WED...CANADIAN HIGH PRESSURE WILL SPREAD EWD INTO THE
NERN STATES THU AND THU NIGHT...EXTENDING SOUTHWARD ENOUGH TO
REINFORCE THE ALREADY COOL AIR IN PLACE OVER THE CWFA. WITH UPPER
TROUGH AXIS ALREADY EAST OF THE AREA...SUBSIDENCE IS IMPLIED AND PROG
SOUNDINGS FROM NAM/GFS INDICATE CAPPING ALOFT THOUGH THE GFS LAPSE
RATES ARE FAVORABLE ENOUGH TO THINK A FEW TOWERING CU COULD GO UP. AN
EMBEDDED SHORTWAVE WILL DRIFT OVER THE AREA EARLY IN THE DAY ALBEIT
WITHOUT MUCH MOISTURE TO WORK WITH. WILL INCLUDE A SCHC POP AHEAD OF
THE WAVE BUT EXPECT AFTN CONVECTION TO BE INHIBITED.

A CAD EVENT WILL TAKE SHAPE BY THE END OF THE DAY THU AS THE SFC HIGH
SHIFTS ACRS THE MTNS. FRIDAY THE UPPER FLOW WEAKENS OVER THE
AREA...WITH BOTH NAM/GFS BASICALLY SHOWING THE TROUGH FILLING OVER
THE SOUTHEAST. THE PARENT HIGH STAYS IN MOTION AS A RESULT...MOVING
OFFSHORE BUT MAINTAINING RIDGING DOWN THE ERN SEABOARD. THE
SUBSIDENCE ALOFT BEING WEAKER...CAPPING IS LESS CERTAIN DURING
HEATING FRIDAY AFTN. ALLOWED A SCHC POP TO RETURN TO THE FCST IN THE
MOST FAVORED AREA...ALONG THE BLUE RIDGE WHERE EASTERLY UPSLOPE FLOW
WILL ENHANCE DEVELOPMENT.  US MODELS BEAR THEIR USUAL DISCREPANCIES
IN TERMS OF CAPE...BUT AGREE THAT SHEAR WILL BE VERY WEAK AND
PROFILES QUITE DRY THROUGH A DEEP LAYER. WE/D PROBABLY BE DEALING
WITH PULSE STORMS POSING A DAMAGING WIND THREAT IF CELLS WERE TO
DEVELOP.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 300 PM TUE...UPPER TROF BRIEFLY BUILDS INTO THE AREA EARLY IN
THE MEDIUM RANGE AS AN UPPER TROF MOVES OFF SHORE. ANOTHER UPPER
TROF BUILDS OVER THE ERN CONUS ON MON AND REMAINS ON TUE. AT THE
SFC...HIGH PRESSURE REMAINS RIDGED INTO THE AREA FROM THE NORTH WITH
A MODERATING AIR MASS UNTIL A COLD FRONT CROSSES THE AREA MONDAY.
HIGH PRESSURE BEGINS TO BUILD IN AS THE FRONT SLOWLY MOVES EAST ON
TUE. EXPECT A DRY FCST FRI AND SAT...WITH ONLY A SLIGHT CHC OF
PRECIP MOVING IN ACROSS THE WEST AHEAD OF THE FRONT ON SUN. MTNS
WILL SEE THE BEST CHC OF PRECIP MON WHERE MOISTURE AND FORCING ARE
HIGHEST. PRECIP CHC DIMINISHES TO SLIGHT CHC FOR TUE AND MAINLY
OUTSIDE OF THE MTNS IN THE LINGERING MOISTURE BEHIND THE SLOW MOVING
FRONT. BELOW NORMAL TEMPS RISE TO A LITTLE ABOVE NORMAL AHEAD OF THE
FRONT...THEN DROP A LITTLE BELOW NORMAL BEHIND THE FRONT ON TUE.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...ANOTHER LOW CONFIDENCE FORECAST THIS PERIOD...AS A NUMBER
OF COMPETING FACTORS WILL DETERMINE THE SIGNIFICANCE OF FLT
RESTRICTIONS LATER THIS MORNING. A LIFR CIG RECENTLY DEVELOPED...
LIKELY AS A RESULT OF A WET GROUND DUE TO HEAVY RAIN THAT FELL
AROUND THE TERMINAL EARLIER. HOWEVER...THIS IS NOT ANTICIPATED TO
STICK AROUND...AS INCREASING (ALBEIT LIGHT) NE WINDS SHOULD BEGIN TO
BRING SLIGHTLY DRIER AIR INTO THE AREA. NEVERTHELESS...WITH THE WET
GROUND AND PLENTY OF LINGERING MOISTURE...EXPECT LMVFR CIGS TO
DEVELOP BY DAYBREAK. CERTAINLY CANNOT RULE OUT IFR CONDITIONS
REDEVELOPING...BUT JUST DON/T HAVE THE CONFIDENCE TO FORECAST THESE
CONDITIONS ATTM. ONCE THE MVFR CIGS DEVELOP...THEY SHOULD BE SLOW TO
LIFT LATER TODAY...AND ARE  ACTUALLY EXPECTED TO REMAIN THROUGH THE
PERIOD. SHOWER REDEVELOPMENT MAY OCCUR IN THE VCNY OF THE TERMINAL
DURING THE AFTERNOON... ALTHOUGH COVERAGE SHOULD REMAIN ISOLATED AND
A TAF MENTION IS NOT WARRANTED ATTM. OTHERWISE...LIGHT NE WINDS
SHOULD DEVELOP OVER THE NEXT COUPLE OF HOURS...AND PERSIST THROUGH
THE PERIOD.

ELSEWHERE...MADE SOMEWHAT RADICAL CHANGES TO THE KAVL TAF...AS A
PERSISTENT UP-VALLEY WIND...AND DEVELOPMENT OF MVFR STRATOCU IS
RESULTING IN A TEMP/DEWP SPREAD THAT IS MAKING DEVELOPMENT OF
SUB-MVFR CONDITIONS LESS LIKELY...AND THIS IS SOMEWHAT SUPPORTED BY
THE LATEST SHORT TERM GUIDANCE. HOWEVER...SUSPECT THAT WINDS WILL
EVENTUALLY DIMINISH...AND IFR CONDITIONS COULD STILL VERY WELL
DEVELOP BY DAYBREAK...SO A TEMPO FOR 2SM/BKN004 WAS INCLUDED AFTER
10Z. OTHERWISE...THE FORECASTS FOR KGSP/KHKY ARE QUITE PROBLEMATIC
AND LOW CONFIDENCE...AS LIGHT NE WINDS AND VFR STRATOCU HAVE BECOME
ESTABLISHED (WHICH WOULD ARGUE AGAINST LOW STRATUS/FOG
DEVELOPMENT)...BUT ON THE OTHER HAND THE SOIL IS VERY WET (ESP NEAR
KGSP) AND LOW LEVEL MOISTURE REMAINS PLENTIFUL. NEVERTHELESS...WILL
COUNT ON THE DEEP NE FLOW EVIDENT ON LATEST RADAR WIND PROFILE
DISPLAY AND AFOREMENTIONED FACTORS KEEPING CONDITIONS AT LMVFR OR
BETTER LATER THIS MORNING. MEANWHILE...AM A LITTLE MORE CONFIDENT
THAT CONDITIONS SHOULD BE NO WORSE THAN MVFR AT KAND/KGMU. CIGS
SHOULD PERSIST IN THE VFR/MVFR RANGE THROUGH MUCH OF THE DAY...
ALTHOUGH CLOUDS MAY SCATTER AT KAND AS SOME DRIER AIR ARRIVED FROM
THE WEST.

OUTLOOK...ALTHOUGH THE CHANCES FOR DIURNAL CONVECTION WILL GREATLY
DIMINISH AFTER WEDNESDAY...THE POTENTIAL FOR LATE NIGHT/MORNING
FOG/STRATUS WILL PERSIST INTO LATE WEEK...ESP IN THE MTN VALLEYS.
CONDITIONS MAY FINALLY DRY OUT FOR THE WEEKEND.

CONFIDENCE TABLE...

            08-14Z        14-20Z        20-02Z        02-08Z
KCLT       HIGH  83%     HIGH  88%     MED   72%     MED   78%
KGSP       MED   78%     MED   71%     HIGH 100%     HIGH  92%
KAVL       MED   71%     MED   76%     HIGH  80%     HIGH  80%
KHKY       MED   72%     MED   79%     MED   71%     MED   67%
KGMU       HIGH  80%     MED   70%     HIGH 100%     HIGH  92%
KAND       HIGH  95%     HIGH  95%     MED   78%     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...JDL
NEAR TERM...JDL
SHORT TERM...WIMBERLEY
LONG TERM...WIMBERLEY
AVIATION...JDL






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.