Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 271729
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
129 PM EDT SAT SEP 27 2014

.SYNOPSIS...
HIGH PRESSURE WILL PERSIST ACROSS THE REGION TODAY...AND
WILL WEAKEN ON SUNDAY. A WEAK LOW PRESSURE SYSTEM WILL MOVE
NORTHWARD FROM THE GULF OF MEXICO SUNDAY NIGHT AND MONDAY AND WILL
SPREAD RAIN ACROSS THE REGION. THE LOW SHOULD MOVE SLOWLY AWAY TO
THE NORTHEAST MONDAY NIGHT AND TUESDAY WITH COOL HIGH PRESSURE
BUILDING IN FROM THE NORTHEAST ON WEDNESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
130 PM EDT UPDATE...THE FCST GRIDS ARE IN GOOD SHAPE WITH ONLY
MINOR TWEAKS NEEDED TO SKY AND HR/LY TEMPS.

1030 AM EDT UPDATE...LATEST VIS IS SHOWING LOW BASED CU DEVELOPING
WITHIN THE WEDGE DURING THE PAST HR. ENOUGH MOISTURE IS AVAILABLE TO
ENABLE THE DEVELOPMENT OF CIGS ACROSS THE NC PIEDMONT AND FTHILLS.
EXPECT CONTINUED AREAL CU DEVELOPMENT THROUGH THE NEXT FEW HRS. THE
SKY GRIDS HAVE BEEN ADJ ACCORDINGLY. THE LOW BASES COULD BECOME AN
AVIATION CONCERN AT KCLT. HOURLY TEMP CURVES ARE RUNNING VERY CLOSE
TO FCST/D VALUES WITH ONLY MINOR TWEAKS NEEDED.

AS OF 635 AM...I WILL UPDATE THE FORECAST TO REDUCE SKY
COVER...ESPECIALLY NORTH THE NC/SC LINE. LATEST SATELLITE TRENDS
INDICATE THAT CIRRUS WILL STREAM OVER THE REGION INTO THIS EVENING.
I WILL UPDATE TO TWEAK SKY...TEMP...AND WINDS.

AS OF 315 AM...LATEST IR SATELLITE IMAGES INDICATED THE CLEARING
LINE BEHIND A LARGE PATCH OF STRATUS REACHED THE GSP AREA. THESE
CLOUDS SHOULD CONTINUE TO DRIFT SW THROUGH THIS MORNING...LEAVING
SCT TO BKN CIRRUS CLOUDS. DRIER MID LEVEL AIR WILL SPREAD ACROSS THE
REGION AS SFC TO MID LEVEL HIGH PRESSURE PIVOTS ACROSS NEW ENGLAND.
TODAY...THE REGION SHOULD SEE AN INCREASE IN INSOLATION COMPARED TO
THE PAST WEEK. AS A RESULT...HIGH TEMPERATURES ARE FORECAST TO RANGE
FROM 3 TO 7 DEGREES WARMER THAN FRIDAY. A STEADY NORTHEAST WIND WILL
REMAIN THROUGH TODAY...CONDITIONS WILL REMAIN DRY.

TONIGHT...CONDITIONS WILL CHANGE VERY LITTLE FROM TODAY.
HOWEVER...DURING THE LATE NIGHT HOURS ISENTROPIC LIFT BETWEEN
305K-315K IS EXPECTED TO SLOW INCREASE FROM SW TO NE. IN
ADDITION...MOISTURE CONTENT WITHIN THE LLVL WILL LIKELY
INCREASE...RESULTING IN INCREASE CLOUD COVER FROM SW TO NE. I WILL
ALSO MENTION PATCHES OF SCHC POPS. LOW TEMPERATURES ARE FORECAST TO
RANGE FROM THE MID 50S WITHIN THE MTN VALLEYS TO LOW 60S EAST.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 230 AM SATURDAY...THE MAIN CONCERN FOR THE SHORT RANGE IS THE
AMOUNT OF RAINFALL EXPECTED SUNDAY NIGHT AND MONDAY. THE MODELS ARE
IN GENERAL AGREEMENT WITH WEAKENING A COLD AIR DAMMING WEDGE ACROSS
THE WESTERN CAROLINAS ON SUNDAY AS AN UPPER ANTICYCLONE MOVES OFF
THE MID ATLANTIC COAST AND BREAKS DOWN...TAKING WHAT IS LEFT OF THE
PARENT HIGH ALONG WITH IT. SOME LIGHT PRECIP MAY BREAK OUT AS MOIST
UPGLIDE BEGINS ALONG THE BLUE RIDGE AND DEEPER MOISTURE MOVES UP
FROM THE SW THROUGH THE DAY. FROM THAT POINT ONWARD...MID/UPPER
SUPPORT INCREASES...PARTICULARLY IN THE FORM OF UPPER DIVERGENCE AS
THE RIGHT ENTRANCE REGION OF A JET STREAK MOVES OVERHEAD...ALONG
WITH DEEP MOISTURE FROM THE GULF. BY SUNDAY MORNING...IT APPEARS
THAT DEEP CONVECTION ALONG THE GULF COAST HAS ALREADY GIVEN THE
MODELS VARYING DEGREES OF FITS. A LOW LEVEL PV ANOMALY SEEN IN THE
GFS OVER MS/AL AND SEEN IN THE NAM OVER AL CAN BE TRACKED ACROSS THE
SE AND CAROLINAS THROUGH MONDAY. THESE FEATURES APPEAR RESPONSIBLE
FOR STRONG LOW LEVEL FORCING THAT RESULTS IN A PRECIP BULLSEYE THAT
MOVES ACROSS THE FCST AREA MAINLY MONDAY. TO WHAT EXTENT THIS
CONVECTION ACTUALLY DEVELOPS AND MOVES N OR NE IS QUESTIONABLE. AT
THIS POINT...IT SEEMS REASONABLE TO INCREASE THE PRECIP CHANCES A
BIT MORE ON SUNDAY NIGHT AND MONDAY...WHICH INCREASES THE EXTENT OF
THE CATEGORICAL POP MAINLY OVER THE MTNS AND FOOTHILLS. HOWEVER...
CONFIDENCE IN HEAVY RAINFALL OR THE POSSIBLE LOCATION OF HEAVY RAIN
IS NOT ANY GREATER. THE NEW DAY2 EXCESSIVE RAINFALL OUTLOOK FROM WPC
ALSO SUGGESTS LESS OF A THREAT FOR HEAVY RAIN OVER THE WRN
CAROLINAS. SO...WILL KEEP IT OUT OF THE HWO FOR NOW. AS FOR THE REST
OF THE SHORT RANGE...THE SYSTEM WILL MOVE FAIRLY SLOWLY SO A HIGH
POP WILL LINGER OVER THE EAST INTO MONDAY EVENING. PRECIP CHANCES
WILL SLOWLY RAMP DOWN FROM THE WEST MONDAY NIGHT AS THE SURFACE LOW
MOVES OFF TO THE EAST. THE COOLER SIDE OF GUIDANCE IS FAVORED FOR
HIGH TEMPS GIVEN THE PRECIP AND CLOUD COVER.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 315 AM EDT SATURDAY...THE NEW GUIDANCE CONTINUES TO PORTRAY A
SLOW MOVING SHORT WAVE MOVING ACROSS THE CAROLINAS ON TUESDAY...
WHICH DEAMPLIFIES AS IT GETS SWALLOWED UP OR INCORPORATED BY AN
UPPER LOW TO THE N. THE SLOW MOVEMENT OF THE SURFACE LOW OVER THE
ERN CAROLINAS SUGGESTS THAT A SMALL PRECIP CHANCE MAY LINGER ACROSS
THE REGION THROUGH MOST OF THE DAY...SO SOME BACKWARD TIMING
ADJUSTMENT WAS MADE TO RETAIN A SLIGHT CHANCE IN THE FCST. AFTER
THAT...EXPECT A DRY FCST WITH AN UPPER RIDGE AND SURFACE HIGH
PRESSURE. NO SIGNIFICANT CHANGES WERE MADE FOR WEDNESDAY OR
THURSDAY. BY FRIDAY...THE NEXT STRONG SHORT WAVE SHOULD BE
APPROACHING FROM THE WEST. ALTHO SOME RUN-TO-RUN CONSISTENCY ISSUES
ARE APPARENT...THE ECMWF AND GFS ARE FAIRLY CONSISTENT WITH EACH
OTHER APART FROM MINOR TIMING DIFFERENCES. THESE MODELS DRIVE AN
ACTIVE COLD FRONT ACROSS THE REGION IN THE FRIDAY AFTERNOON TO
SATURDAY MORNING TIME FRAME. SO...A SECOND ADJUSTMENT WILL BE MADE
LATE IN THE PERIOD...TO RAISE PRECIP PROBABILITY INTO THE CHANCE
RANGE ACROSS MORE OF THE FCST AREA AND TO EXPAND THE CHANCE INTO THE
FRIDAY NIGHT PERIOD.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
AT KCLT...VFR CONDS EXPECTED THROUGH THE PERIOD. FEW TO SCT CU WILL
PERSIST THIS AFTERNOON...BUT REMAIN ABV 030. LOW TO MID LEVEL ATL
MOISTURE FLUX WILL COMMENCE OVERNIGHT WHICH WILL BRING IN
CLOUDS...BUT NOT ENOUGH FOR A RESTRICTIVE CIG MENTION. THESE CLOUDS
WILL ALSO OFFSET MUCH A VSBY CONCERN ARND DAYBREAK.

ELSEWHERE...VFR CONDS WILL PERSIST THROUGH MOST OF THE TAF PERIOD
WITH LINGER LOW VFR CU THROUGH THE AFTERNOON. ATL MOISTURE FLUX WILL
BRING IN MVFR CLOUDS FAIRLY LATE...ARND DAYBREAK WHICH SHOULD AFFECT
ALL TERMINALS THROUGHOUT THE MORNING...WITH CIGS LIFTING TO VFR
PROBABLE NEAR THE END OF THE TAF PERIOD.

OUTLOOK...HIGH LEVELS MOISTURE WILL RETURN FOR THE START OF THE WORK
WEEK ASSOCIATED WITH AN AREA OF UNSETTLE WEATHER MOVING NORTH OUT OF
THE GULF OF MEXICO. PERIODS OF CONTINUOUS MODERATE TO HEAVY RAINFALL
WILL AFFECT THE AREA MON/TUE PRODUCING LOW CIGS AND VSBY.

CONFIDENCE TABLE...

            17-23Z        23-05Z        05-11Z        11-17Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     MED   78%
KAVL       HIGH 100%     HIGH 100%     MED   68%     MED   69%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     MED   79%
KGMU       HIGH 100%     HIGH 100%     HIGH 100%     MED   78%
KAND       HIGH 100%     HIGH 100%     HIGH 100%     HIGH  82%

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...PM
NEAR TERM...NED/SBK
SHORT TERM...PM
LONG TERM...PM
AVIATION...SBK





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