Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 280735
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
335 AM EDT SUN SEP 28 2014

.SYNOPSIS...
HIGH PRESSURE WILL WEAKEN TODAY AS LOW PRESSURE ORGANIZES OVER THE
NORTHERN GULF OF MEXICO. THE LOW PRESSURE SYSTEM WILL MOVE NORTHWARD
FROM THE GULF OF MEXICO TONIGHT 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. A COLD FRONT WILL ARRIVE FROM THE
NORTHWEST LATE IN THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 330 AM...RECENT SATELLITE IMAGES INDICATED THAT BKN TO OVC
CIRRUS WAS COVERING THE DEEP SOUTH REGION...LIFTING NORTH ACROSS THE
CWA. IN ADDITION...HIGH PRESSURE CENTERED OFF THE MID ATLANTIC COAST
WILL ADVECT MID LEVEL MOISTURE ACROSS GA/SC...INCREASING SHARPLY
AFTER 18Z. I WILL FORECAST INCREASING SKY COVER THROUGH THE DAY.
MODEL QPF REMAINS VERY LIMITED ACROSS THE REGION TODAY...BEST CHCS
ACROSS THE MTNS. IT APPEARS THAT MOST AREAS WILL REMAIN DRY...BUT
CHC POPS WILL BE USED ACROSS THE FAVORED MTN AREAS THIS AFTERNOON.
TEMPERATURES ARE FORECAST TO PEAK IN THE L70S ACROSS THE MTNS TO MID
TO U70S ACROSS THE FOOTHILLS AND PIEDMONT. HIGH TEMPERATURES WILL BE
LIMITED BY STEADY LIGHT NE WINDS AND BUILD CLOUD COVER.

TONIGHT...NAM INDICATES THAT ISENTROPIC LIFT WILL BEGIN BETWEEN 6Z
TO 9Z...WITH A BAND OF 305K TO 315K OMEGA ACROSS THE FOOTHILLS AND
EAST FACING SLOPES. THE COMBINATION OF DEEP MOISTURE...STRENGTHENING
ISENTROPIC LIFT...AND UPSLOPE FLOW WILL SUPPORT POPS RISING FROM CHC
DURING THE LATE EVENING TO CATE BY DAWN. INSTABILITY MAY REMAIN
NEARLY ZERO OVERNIGHT...SUPPORTING ONLY A MENTION OF SHOWERS. QPF
HAS BEEN SIGNIFICANTLY REDUCED BASED ON LATEST NATIONAL GUIDANCE.
LOW TEMPERATURES ARE FORECAST TO RANGE FROM NEAR 60 ACROSS THE MTNS
TO MID 60S EAST.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 245 AM SUNDAY...THE MAIN CONCERN THROUGH THE SHORT RANGE
CONTINUES TO BE THE THREAT OF HEAVY RAIN ON MONDAY. RAIN STILL LOOKS
LIKE A SAFE BET FOR MONDAY GIVEN THE DEGREE OF UPPER DIVERGENCE
PROVIDED BY THE RIGHT ENTRANCE REGION OF THE UPPER JET...AND THE
EXPECTED MID LEVEL ISENTROPIC LIFT AND VORTICITY ADVECTION...ALL TO
ACT UPON DEEP MOISTURE WITH PW ABOVE 150% OF NORMAL. THUS...
EXPANDING THE CATEGORICAL POP WAS AN EASY DECISION FOR MONDAY. TEMPS
WERE ADJUSTED DOWN A BIT AS WELL. IT SHOULD BE A RAINY DAY. ITS THE
AMOUNT THAT IS PROBLEMATIC. THE LATEST GUIDANCE SUGGESTS THAT NOT
ALL THE NECESSARY INGREDIENTS WILL COME TOGETHER. IT IS LIKELY THAT
AN IN-SITU WEDGE OR REMNANT COOL POOL WILL REMAIN IN PLACE NEGATING
ANY SURFACE BASED CAPE. THE MODELS DEVELOP AN 850 MB LOW TO THE
SOUTH WHICH KEEPS THE 850MB WIND MORE NORTHEASTERLY...WHICH CUTS
DOWN ON MECHANICAL FORCING NEAR THE BLUE RIDGE. A BIG PROBLEM COULD
BE THE DEVELOPMENT OF DEEP CONVECTION IN THE WARMER AIR CLOSER TO
THE GULF COAST...OR AT LEAST ALONG A WEDGE BOUNDARY...WHICH WOULD
LIMIT THE MOISTURE FLUX TOWARD THE WRN CAROLINAS AND NE GEORGIA. THE
MODELS CONTINUE TO STRUGGLE WITH THE DEVELOPMENT OF LOW LEVEL PV
ANOMALIES THAT DRIVE PATCHES OF EXCESSIVE RAINFALL IN THE MODEL
OUTPUT...THE LOCATION OF WHICH HAS BEEN INCONSISTENT FROM ONE RUN TO
THE NEXT. BOTTOM LINE...WOULD NOT BET THE FARM ON ENOUGH RAIN TO
CAUSE ANY FLOODING...SO NO WATCHES ARE CONTEMPLATED. THE HWO ALREADY
MENTIONS HEAVY RAIN SO THAT DIE HAS BEEN CAST...AND SO HEAVY RAIN
WILL CONTINUE TO BE MENTIONED AS A MATTER OF COURSE.

THE PRECIP CHANCES ARE RAMPED DOWNWARD MONDAY NIGHT AND TUESDAY
MORNING PER THE MORE PROGRESSIVE GFS AND ECMWF. HAVE PROVIDED A
TREND TOWARD ENDING THE PRECIP CHANCES EARLIER ON TUESDAY AFTERNOON
AS WELL. THIS POP TREND SUGGESTS A WARMING TEMP TREND FOR TUESDAY AS
WELL...BUT THAT DAY HAS BUST POTENTIAL DEPENDING ON WHETHER OR NOT
THE FLOW AT 850MB COMES AROUND TO DOWNSLOPE E OF THE MTNS IN THE
AFTERNOON. HAVE RAISED TEMPS A FEW DEGREES. THE REST OF THE SHORT
RANGE IS QUIET AND RELATIVELY DRY AS HIGH PRESSURE RIDGES BACK DOWN
FROM THE NORTH TUESDAY NIGHT.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 320 AM SUNDAY...THE LATEST MEDIUM RANGE GUIDANCE GENERALLY
SUPPORTS THE ONGOING FORECAST. AN UPPER RIDGE WILL BUILD OVER THE
REGION ON WEDNESDAY AND WEDNESDAY NIGHT THAT WILL SUPPORT HIGH
PRESSURE OVER THE REGION THROUGH THURSDAY. AM NOT INCLINED TO PUT
MUCH STOCK IN THE LOW QPF GENERATED BY THE GFS IN THE EASTERLY
UPSLOPE AREAS FOR THE MIDDLE PART OF THE WEEK AND THUS THE FCST WAS
KEPT DRY FOR WEDNESDAY AND THURSDAY. THE MODELS SHOW DECENT
RUN-TO-RUN CONSISTENCY WITH THE PROGRESSION OF THE NEXT UPPER WAVE
LATE IN THE WEEK...ALTHO THEY STILL SHOW SOME TIMING DIFFERENCES
WITH THE PASSAGE OF AN ASSOCIATED COLD FRONT. THINK THE FCST CHANCE
OF PRECIP FOR FRIDAY AFTERNOON AND FRIDAY NIGHT HAS THIS WELL IN
HAND. NO CHANGES WERE MADE TO THE MEDIUM RANGE.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE...A WEAK RIDGE OF SFC HIGH PRESSURE WILL
REMAIN ACROSS THE WESTERN CAROLINAS THROUGH THE 6Z TAF PERIOD. THIS
PATTERN WILL PROVIDE LIGHT NORTHEAST WINDS...PERIODS OF CALM
EXPECTED BEFORE SUNRISE. BASED ON RECENT SATELLITE TRENDS AND
GUIDANCE...I WILL INDICATE BKN CLOUDS WITH BASES BETWEEN 050-060 KFT
ALONG WITH CIRRUS. WIDESPREAD RAIN WILL LIKELY SPREAD SW TO NE AFTER
6Z MON.

OUTLOOK...HIGH LEVELS OF 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 CIG AND VSBY
RESTRICTIONS.

CONFIDENCE TABLE...

            07-13Z        13-19Z        19-01Z        01-07Z
KCLT       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGSP       HIGH  99%     HIGH  94%     HIGH  96%     HIGH 100%
KAVL       MED   74%     HIGH  91%     HIGH  96%     HIGH  92%
KHKY       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH  99%     HIGH  96%     HIGH 100%     HIGH 100%
KAND       HIGH  98%     HIGH  94%     HIGH  98%     HIGH  89%

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
SHORT TERM...PM
LONG TERM...PM
AVIATION...NED






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