Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 171135
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
735 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/...
AS OF 7 AM...A FEW SPOTTY SHOWERS HAVE BEEN DOTTING THE UPSTATE THIS
MORNING...JUST NORTH OF THE FRONTAL BOUNDARY AND WITHIN AN AREA
OF LINGERING ELEVATED INSTABILITY. A SLIGHT CHANCE HAS BEEN PULLED
INTO THE UPSTATE FOR THIS MORNING...BUT EVEN THIS MAY BE
OVERSTATING THE SITUATION A BIT. OTHERWISE...STRATOCU SHOULD
CONTINUE TO EXPAND ACROSS THE AREA...AND MOST LOCATIONS SHOULD SEE
CLOUDY/MOSTLY CLOUDY SKIES INTO LATE MORNING.

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 615 AM WED...NO WHOLESALE CHANGES TO THE EXPECTATIONS FOR THE
WEEKEND AND EARLY NEXT WEEK. ON SATURDAY THE PARENT HIGH ASSOCIATED
WITH THE LATE-WEEK COLD AIR DAMMING WILL BE FORCED FURTHER OFFSHORE.
EASTERLY FLOW MAY CONTINUE IN THE LOW LEVELS...BUT THE INFLUENCE OF
THE WEDGE WILL BE MINIMAL. THE PATTERN SHIFTS AND RETURN FLOW BEGINS
SUNDAY AHEAD OF THE NEXT SYSTEM AFFECTING THE ERN CONUS. A WEAK AREA
OF LOW PRESSURE OFF THE SOUTHEAST COAST IS SHOWN ON BOTH GFS/EC BUT
DOES NOT APPEAR TO HAVE AN IMPACT THIS FAR INLAND. POPS WILL REMAIN
UNMENTIONABLY LOW. TROUGH DIGS INTO THE OHIO VALLEY AND MID-ATLANTIC
SUNDAY NIGHT...ACCOMPANIED BY A COLD FRONT. GFS CONTINUES TO BE A
LITTLE FASTER THAN THE EC IN BRINGING THE FRONT INTO THE AREA...AND
THE EC DEPICTION OF THE TROUGH CONTINUES TO BE STRONGER. POPS MONDAY
APPEAR TO BE A BIT HIGHER THAN CLIMO THOUGH NEITHER MODEL DEVELOPS
SIGNIFICANT QPF AT THIS TIME. BOTH GFS/EC DO SHOW SOME INSTABILITY
AHEAD OF THE FROPA. TEMPS INCREASE SLIGHTLY EACH DAY THRU
MONDAY...WITH MAXES AROUND CLIMO THAT DAY. THEY THEN DROP A COUPLE
CATEGORIES FOR TUESDAY.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AT KCLT...IFR CIGS SHOULD LIFT TO MVFR BY 14Z OR SO...THEN WILL
LIKELY BE SLOW TO LIFT TO VFR...WHICH IS NOT EXPECTED TO OCCUR UNTIL
EARLY AFTERNOON. SHOWER REDEVELOPMENT MAY OCCUR IN THE VCNY OF THE
TERMINAL THIS AFTERNOON...BUT COVERAGE I STILL EXPECTED TO REMAIN
ISOLATED...AND A TAF MENTION IS NOT WARRANTED ATTM. OTHERWISE...
LIGHT NE WINDS SHOULD GENERALLY PERSIST THROUGH THE PERIOD. LOW CIGS
WILL LIKELY REDEVELOP LATE TONIGHT...AND HAVE MAINTAINED CIGS AT THE
LOW END OF THE MVFR CATEGORY FOR NOW.

ELSEWHERE...MVFR CIGS ARE EXPECTED TO PERSIST OR DEVELOP AT MOST
TERMINALS THIS MORNING (THE LIKELY EXCEPTION BEING KAND). CIGS
SHOULD LIFT TO VFR DURING LATE MORNING/EARLY AFTERNOON...AND MAY
EVEN SCATTER OUT FROM TIME TO TIME...ESP AT THE UPSTATE SC
TERMINALS. OTHERWISE...LIGHT NE WINDS SHOULD GENERALLY PERSIST
THROUGH THE PERIOD. LOW CIGS WITH POSSIBLE MTN VALLEY FOG WILL
LIKELY REDEVELOP LATE TONIGHT...AND HAVE MAINTAINED THE FLT CATEGORY
AT THE LOW END OF MVFR FOR NOW.

OUTLOOK...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. A COLD FRONT MAY BRING INCREASING
CHANCES FOR SHOWERS/TSTMS EARLY NEXT WEEK.

CONFIDENCE TABLE...

            11-17Z        17-23Z        23-05Z        05-11Z
KCLT       MED   69%     HIGH  86%     HIGH  82%     HIGH  83%
KGSP       HIGH  82%     HIGH  92%     HIGH 100%     HIGH 100%
KAVL       HIGH  81%     HIGH  85%     HIGH  84%     HIGH  85%
KHKY       HIGH  89%     HIGH  83%     HIGH  96%     HIGH  83%
KGMU       HIGH  84%     HIGH  91%     HIGH 100%     HIGH  98%
KAND       HIGH  94%     HIGH  98%     HIGH 100%     HIGH  95%

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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