Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 232142
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
542 PM EDT TUE SEP 23 2014

.SYNOPSIS...
COOL HIGH PRESSURE WILL REMAIN OVER THE REGION THROUGH THE END OF
THE WORK WEEK. MOISTURE AND RAIN CHANCES INCREASE OVER THE WEEKEND
AND EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 535 PM...LATEST RADAR IMAGE INDICATED A WEAKENING AREA OF
LIGHT RAIN ACROSS THE UPPER I-77 CORRIDOR. RECENT MODELS RUNS SHOW
THAT THIS AREA OF LIGHT RAIN WILL LIKELY WEAKEN THROUGH THE EVENING
HOURS. I WILL UPDATE THE FORECAST TO ADJUST POP TREND. I WILL ALSO
REWORK TEMPERATURES TO REFLECT COOLER OBSERVATIONS...RESULTING IN A
DEGREE DECREASE TO TONIGHT/S LOW.

PREVIOUS DISCUSSION...
UPPER LOW SPINNING ATOP THE REGION THIS AFTERNOON WILL CONTINUE TO
SLOWLY FILL AND LARGER SCALE FORCING ALONG IT/S EAST SIDE SHOULD
WEAKEN AND SHIFT FURTHER TOWARD THE EASTERN CAROLINAS THROUGH
TONIGHT. SFC RIDGING WILL REMAIN NOSED SWWD INTO THE CWFA AS WELL
BUT WITH SHARPENING SFC COASTAL TROUGH...ENUF BACK OF THE FLOW IN
THE LOWEST LVLS SHOULD LEAD TO DIMINISHING FTHL/PIEDMONT LIGHT PCPN
CHANCES THIS EVENING. ENUF MIXING IS LIKELY TO LIMIT FOG DEVELOPMENT
OVERNIGHT TO JUST THE MTN VALLEYS. UNLIKE ACRS THE PIEDMONT
TODAY...DEEPER MOISTURE WILL BE DISPLACED FURTHER EASTWARD ON
WEDNESDAY...BUT A WITH THE MODEL CONSENSUS FEATURING A RESURGENCE OF
ATLANTIC FETCH EASTERLY FLOW...WILL PLAN ON SPREADING SHOWER CHANCES
BACK IN FROM EAST.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
AS OF 230 PM EDT TUESDAY...FOR WED NIGHT AND THURSDAY...A CLOSED
UPPER LOW OVER THE REGION WILL OPEN UP AS IT PULLS NE WHILE A RIDGE
OF H5 HIGH CENTERED OFF THE SE COAST WILL SLOWLY RETROGRADE TOWARDS
THE GULF THRU THU. AT THE SURFACE...LATEST MODELS CONTINUE TO AGREE
THAT A DEVELOPING SURFACE LOW OVER THE NC COASTAL PLAINS WILL LIFT
NORTH ALONG THE ATLANTIC COAST WHILE A COOL AIR WEDGE REMAINS IN
PLACE OVER THE FORECAST AREA WED NIGHT INTO THU. DEEP MOISTURE
WRAPPING AROUND THE LOW WILL BRING AREAS OF LIGHT RAIN MAINLY TO THE
WESTERN NC PIEDMONT WED NIGHT. HENCE...HAVE MENTIONED LOW END CHANCE
FOR RAIN ALONG AND EAST OF THE I-77 WITH A SLIGHT CHANCE POPS OVER
THE UPSTATE SC AND NC MTNS/FOOTHILLS. AS THE LOW PULLS NE AWAY FROM
THE REGIONAL THU...WEAK ISENTROPIC LIFT ATOP THE SURFACE WEDGE WILL
SET UP...YIELDING A SLIGHT CHANCE FOR RAIN FOR MOST LOCATIONS.
TEMPERATURES SHOULD REMAIN 5-10 DEGREES BELOW NORMAL

THU NIGHT AND FRI....AN UPPER RIDGE OF HIGH CONTINUES TO BUILD OVER
THE GULF STATES WHILE ANOTHER UPPER RIDGE OF HIGH AMPLIFIES OVER THE
ROCKIES AND GREAT PLAINS...WITH A CLOSED UPPER LOW MEANDERING OVER
THE CENTRAL STATES. AT THE SURFACE...A BROAD CANADIAN HIGH PRESSURE
CENTERED OVER THE OHIO VALLEY AND MID ATLANTIC STATES WILL CONTINUE
TO RIDGE SW INTO THE FORECAST AREA. BOTH THE GFS AND ECMWF KEEPS THE
REGION MOSTLY DRY WITH LITTLE TO NO QPF RESPONSE GIVEN THE LACK OF
ISENTROPIC LIFT OVER THE REGION. THE NAM IS AN OUTLIER...SHOWING A
ROBUST QPF RESPONSE ACROSS MUCH OF THE CWA THU NIGHT INTO FRI...AS A
RATHER STRONG SE/S H85 JET OVER THE SURFACE WEDGE PROVIDES GOOD
ISENTROPIC LIFT. IN ADDITION...AREAS OF DPVA WILL MOVE ACROSS THE
REGION AIDING IN ADDITIONAL LIFT. HOWEVER...GIVEN THE MODELS
DISAGREEMENT ON THIS FEATURE...HAVE WARRANTED A SLIGHT CHANCE POPS
FOR RAIN THU NIGHT. TEMPS WILL CONTINUE TO REMAIN 5-10 DEGREES BELOW
NORMAL ON FRI.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 215 PM TUESDAY...THE MEDIUM RANGE FCST PICKS UP AT 00Z ON
SATURDAY WITH BROAD UPPER RIDGING PERSISTING ACROSS MOST OF THE
CONUS AND A WELL DEFINED UPPER TROF DIGGING DOWN OVER THE WEST
COAST. THE MODEL GUIDANCE ALSO INDICATES THAT SOME SORT OF WEAK WEAK
UPPER TROFFING WILL DEVELOP OFF THE ATLANTIC SEABOARD AND AN H5 LOW
MIGHT BE IN PLACE OVER THE CENTRAL OR SOUTHERN PLAINS BY EARLY SAT.
BECAUSE THE UPPER FLOW WILL BE WEAK OVER MOST OF THE CONUS...IT IS
DIFFICULT TO KNOW EXACTLY WHERE THE ABOVE FEATURES WILL DEVELOP AND
HOW LONG THEY COULD PERSIST. AT ANY RATE...OVER THE NEXT COUPLE OF
DAYS THE PERSISTENT UPPER RIDGE WILL BEGIN TO FLATTEN OVER SE CANADA
AS THE WEST COAST TROF SLOWLY DRIFTS EASTWARD. AT THE SAME
TIME...THE MODELS SUGGEST THAT THE CLOSED LOW MENTIONED ABOVE WILL
AMPLIFY AND DEVELOP INTO SOME SORT OF SOUTHERN STREAM TROF THAT
APPROACHES THE FCST AREA BY EARLY NEXT WEEK. OVERALL...THE EVOLUTION
OF THIS UPPER PATTERN REMAINS PRETTY UNCLEAR BEYOND SUN OR OR.

AT THE SFC...HIGH PRESSURE WILL BE CENTERED TO OUR NORTH WITH COOL
NELY LOW LVL FLOW PERSISTING OVER THE FCST AREA. OVER THE NEXT
COUPLE DAYS THE MODELS KEEP THE HIGH NEARLY STATIONARY AND WEAKEN IT
ON SUN. BY EARLY MON...THE ECMWF STILL TRIES TO SPIN UP A LOW OVER
THE NORTHERN GOM/SOUTHERN MISS RIVER VALLEY AND MOVE IT NORTHWARD
THRU NEW DAY 7. THE LATEST 12Z GFS TRIES TO DEVELOP SOMETHING OVER
THE SAME AREA...BUT IS NOT QUITE ABLE TO. BOTH MODELS DO MOVE A
BROAD AREA OF DEEP LYR MOISTURE UP FROM THE GULF AND INTO OUR FCST
AREA BY THE END OF THE MEDIUM RANGE. AS FOR THE SENSIBLE FCST...I
KEPT SAT DRY WITH POPS INCREASING FROM SW TO NE ON SUN AND MON. BY
MON AFTERNOON...I HAVE A SOLID CHANCE OVER MOST OF THE CWFA AND THAT
SOLID CHANCE REMAINS THRU THE REST OF THE PERIOD. TEMPS WERE CHANGED
LITTLE FROM THE PREVIOUS FCST WITH HIGHS IN THE UPPER 70S EACH DAY
AND LOWS WARMING A BIT FROM THE UPPER 50S TO LOW 60S BY NEW DAY 7.

&&

.AVIATION /22Z TUESDAY THROUGH SUNDAY/...
AT KCLT...ONGOING THREAT OF SHOWERS WITHIN THE MODERATE ENE FLOW
WILL REMAIN FOR THE BALANCE OF THE AFTERNOON AS WILL AT LEAST OCNL
LVFR CIGS. WITH DRYING THROUGH A DEEPER LAYER EXPECTED TONIGHT...
MORE IN THE WAY OF SPOTTY STRATO/ALTOCU SHOULD BE SEEN WITH ENOUGH
NE WIND TO PREVENT ANY VSBY RESTRICTIONS.

ELSEWHERE...A SMATTERING OF MVFR/LVFR CIGS ACRS THE CWFA THIS
AFTERNOON SHOULD BE ABLE TO SLOWLY LIFT AS THE AFTERNOON WEARS
BEFORE GIVING WAY TO SUBSTANTIAL CLEARING TONIGHT. FOG DEVELOPMENT
IS EXPECTED TO BE LIMITED TO THE MTN VALLEYS.

OUTLOOK...HIGH PRESSURE BUILDING N OF THE REGION SHOULD KEEP
CONDITIONS MOSTLY VFR...BUT EASTERLY FLOW ATLANTIC MOISTURE COULD
ENCROACH ON THE REGION AT TIMES WED THROUGH THE WEEKEND.

CONFIDENCE TABLE...

            21-03Z        03-09Z        09-15Z        15-21Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH 100%     MED   72%     HIGH  83%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       HIGH  99%     HIGH 100%     HIGH 100%     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...JPT
NEAR TERM...NED
SHORT TERM...JOH
LONG TERM...JPT
AVIATION...CSH





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