Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 190237
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1037 PM EDT FRI APR 18 2014

.SYNOPSIS...
A MOIST LOW PRESSURE SYSTEM WILL MOVE SLOWLY ACROSS SOUTHERN GEORGIA
AND OFF THE SOUTH CAROLINA COAST THROUGH SUNDAY. HIGH PRESSURE WILL
BRIEFLY BUILD IN MONDAY...BEFORE A COLD FRONT CROSSES EAST ON
TUESDAY. A BROAD AND DRY AREA OF HIGH PRESSURE WILL THEN BUILD SOUTH
WEDNESDAY AND LINGER THROUGH THE END OF NEXT WEEK.

&&

.NEAR TERM /THROUGH SATURDAY/...
AS OF 1030 PM EDT FRIDAY...FORECAST REMAINS IN GOOD SHAPE OVERALL
FOR THIS UPDATE.  DID OPT TO TWEAK HOURLY TEMPERATURES OVERNIGHT AS
LATEST TRENDS CONTINUE TO UNDERCUT FCST TRENDS BY A DEGREE OR TWO ON
AVERAGE.  ALSO MADE MINOR ADJUSTMENT TO POPS THROUGH THE EVENING
WHICH CONSISTED OF INCREASING TO SOLID CATEGORICAL LEVELS ACROSS THE
I40 CORRIDOR IN NC.  OTHERWISE LEFT THE REMAINDER OF THE FORECAST AS
IS.

PREVIOUS DISCUSSION...

AS OF 230 PM EDT FRIDAY...BASED ON THE LATEST BUOY REPORTS...IT
APPEARS THE CENTER OF THE SFC LOW OVER THE GULF IS A COUPLE HUNDRED
MILES SOUTH OF THE WESTERN MOST FL PANHANDLE. AN EXPANSIVE AREA OF
RAIN HAS SPREAD ACROSS MOST OF GA AND WRN SC. DRY AIR ASSOCIATED
WITH A DRY WEDGE OF SFC HIGH PRESSURE HAS KEPT PCPN AT BAY OVER MOST
OF THE FA...THOUGH RAIN HAS RECENTLY BEGUN TO FALL OVER THE SRN
UPSTATE. THE LATEST NAM HAS GONE FROM BEING THE DRIEST MODEL OVER
THE FORECAST AREA TO THE WETTEST...WITH A 3 TO 4 INCH QPF BULLSEYE
OVER THE WRN UPSTATE AND NE GA. THE GFS CONTINUES TO BE MUCH MORE
CONSISTENT WITH THE QPF AND GENERAL MASS FIELDS ASSOCIATED WITH THE
LOW. IT/S CURRENT LLVL POT VORT MAX LINES UP WELL WHERE THE HEAVIEST
PCPN IS FALLING...AND LOCAL VWP SHOW THAT ELY WINDS HAVE INCREASED
TO AROUND 40-45 KTS OVER SRN GA.

THE 12 UTC H8 ZONAL WINDS ON THE GFS INCREASE TO 4 TO 5 STANDARD
DEVIATIONS ABOVE NORMAL BY 0600 UTC TONIGHT. THIS SHOULD RESULT IS
STRONG MOISTURE TRANSPORT AND UPGLIDE ACROSS THE LLVL WARM FRONT.
THE GFS ENSEMBLE QPF AVERAGES AROUND 2 INCHES OVER THE UPSTATE AND
SRN NC PIEDMONT AND THIS SEEMS LIKE A REASONABLE AMOUNT FOR THE
EVENT. INTERESTINGLY...THE CANADIAN HAS A 3 INCH QPF MAX NEAR
CHARLOTTE FOR THE EVENT. THAT/S TO SAY...SOME OF THE MODELS REALLY
GO TO TOWN WITH THE DEFORMATION ZONE PCPN...BUT I FEEL MUCH MORE
CONFIDENT STAYING CLOSER TO AN ENSEMBLE BLEND. MY RAINFALL AMOUNTS
ARE NOT HIGH ENOUGH TO WARRANT A FLOOD WATCH...BUT SOME URBAN
FLOODING IS CERTAINLY POSSIBLE FOR THE EVENT. FOR EXAMPLE...THE GFS
H8 ZONAL WIND ANOMALY REMAINS AOA 3 STANDARD DEVIATIONS INTO SUNDAY.
SO WHILE THE MODEL DOZEN/T HAVE MUCH QPF BEYOND MID-DAY SATURDAY...I
WOULD NOT BE SURPRISED TO SEE A NARROW CORRIDOR OF RAIN LAST
CONSIDERABLY LONGER OVER SOME PART OF THE FA.

WENT MUCH LOWER THAN THE NAM MAX TEMPS OVER PARTS OF THE FA
TMRW...MORE IN LINE WITH THE GFS AND WHAT ONE WOULD EXPECT WITH
CLOUDS AND EASTERLY FLOW.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
AS OF 200 PM FRI...STACKED SFC AND UPPER LOW WILL DEPART THE SRN
ATLANTIC COAST SATURDAY EVENING...SLOWLY PROGRESSING EAST AND FURTHER
OFFSHORE THRU SUNDAY. WHILE A FAIR AMOUNT OF LLVL MOISTURE WILL
REMAIN OVER THE AREA SATURDAY NIGHT...THE BEST FORCING WILL HAVE
MOVED EAST WITH THE SYSTEM. HOWEVER NELY 925-850MB WINDS WILL STILL
BE STRONG...BRINGING SOME VERY WEAK LIFT FROM WARM ADVECTION BUT
PERHAPS MORE SIGNIFICANT UPSLOPE FORCING INTO THE BLUE RIDGE. VARIOUS
MODELS CONTINUE TO PRODUCE LIGHT QPF OVERNIGHT. THUS POPS AND CLOUD
COVER ARE SLOW TO TRAIL OFF...LASTING INTO THE MRNG HRS SUNDAY. MIN
TEMPS SUN MRNG WILL BE NEAR NORMAL.

THICKNESSES REBOUND SOMEWHAT THRU THE DAY AS SHORT UPPER RIDGE STARTS
TO BUILD IN THE WAKE OF THE LOW. HOWEVER EAST COAST HIGH PRESSURE
WILL MAINTAIN NELY WINDS AND MAX TEMPS A CATEGORY OR TWO BELOW
NORMAL. THE UPPER RIDGE BUILDS OVERHEAD SUNDAY NIGHT THOUGH IT IS
SOON IMPINGED UPON BY HEIGHT FALLS OVER THE MISSISSIPPI VALLEY
MONDAY. BETWEEN THAT TROUGH AND THE ATLANTIC LOW THE DEGREE OF RETURN
FLOW IS LIMITED BUT SOME MOISTURE DOES ARRIVE SUNDAY NIGHT IN THE
MTNS...ENOUGH TO BRING BACK CLOUD COVER. SOME GUIDANCE DEVELOPS QPF
RESPONSE MONDAY...ALONG WITH SOME DIURNAL INSTABILITY...THOUGH ASCENT
WILL BE HINDERED BY POOR LOW LEVEL LAPSE RATES UNDER THE RIDGE. HAVE
KEPT PRECIP CHANCES BELOW MENTIONABLE VALUES MONDAY. MAX TEMPS RETURN
TO SLIGHTLY ABV CLIMO.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 215 PM FRIDAY...THERE IS FAIRLY GOOD AGREEEMENT IN THE MEDIUM
RANGE AMONGST THE GLOBAL MODELS IN REGARD TO THE UPPER AIR PATTERN
AND RESULTANT SURFACE FEATURES. AN UPPER RIDGE OVER THE REGION
INITIALLY WILL TRANSLATE EASTWARD MON NIGHT WITH A SHORT WAVE
TROUGH TRAVERSING THE AREA ON TUE ALONG WITH A SURFACE COLD FRONT.
MODEL SOUNDINGS DO PRODUCE SOME SBCAPE ON THE ORDER OF 500J/KG TUE
AFTERNOON SO WILL CONTINUE TO MENTION THUNDER. WIND FIELDS DO NOT
LOOK PARTICULARILY STRONG...SO SEVERE THREAT LOOKS MINIMAL AT THIS
JUNCTURE. ANOTHER UPPER RIDGE IS FORECAST TO BUILD OVER THE AREA BY
LATE NEXT WEEK. IN THE MEAN TIME...SURFACE HIGH PRESSURE WILL
MIGRATE FROM THE UPPER MIDWEST ON WED...TO OFF THE CAROLINA COAST BY
LATE THU. AFTER TUE...DRY AND MILD WEATHER IS EXPECTED INTO
FRI...WITH JUST A LOW END CHANCE FOR SOME SCATTERED MOUNTAIN SHOWERS
FRI AFTERNOON WITH INCREASING UPSLOPE FLOW.

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...A MIXTURE OF MVFR/IFR CONDITIONS WILL HIGHLIGHT THIS TAF
CYCLE.  MVFR CONDITIONS WILL PREVAIL FOR THE FIRST FEW HOURS OF THE
TAF CYCLE DUE TO VISB/CIG RESTRICTIONS AS LOWERED CLOUD DECK ADVECTS
IN FROM THE MIDLANDS OF SC IN ASSOCIATION WITH ENHANCED PRECIP
SHIELD.  EXPECTING FURTHER DETERIORATION TO IFR LEVELS AFTER
MIDNIGHT AS MOISTURE FLUX MAXIMIZES DUE TO SURFACE CYCLONE PASSING
BY TO THE SOUTH.  LIKEWISE...ENHANCED PRESSURE GRADIENT FORCES
BETWEEN THE APPROACHING SURFACE HIGH TO THE NORTH...AND THE ABOVE
MENTIONED SURFACE LOW WILL YIELD INCREASING NORTHEASTERLY WINDS WITH
SUSTAINED FLOW IN THE 10-15KTS RANGE AND GUSTS NEARING 26KTS.  THESE
WINDS WILL LIKELY PERSIST THROUGH MUCH OF THIS TAF PERIOD UNTIL THE
SURFACE CYCLONE EJECTS TO THE EAST ALLOWING THE PRESSURE GRADIENT TO
RELAX.  HELD ONTO MENTION OF WX THROUGH 18Z SATURDAY WITH CIGS
RECOVERING TO MVFR LEVELS A FEW HOURS BEFORE THAT.  ENDED TAF WITH
MVFR CIGS AND A PROB30 FOR -RA AS THE SYSTEM EJECTS OUT OF THE
REGION LATE IN THE PERIOD.

SC SITES...MUCH THE SAME AS KCLT ABOVE WITH SLIGHT ADJUSTMENTS TO
TIMING WITH MVFR/IFR CONDITIONS HIGHLIGHTING THE TAF CYCLE.  WINDS
WILL INCREASE AS PRESSURE GRADIENT FORCES RAMP UP WHEN THE SURFACE
LOW PASSES TO THE SOUTH BY EARLY/MID MORNING.  SUSTAINED
NORTHEASTERLY FLOW IN THE 12-15KTS RANGE WITH GUSTS NEARING 28KTS IS
EXPECTED.  ALL WX MENTION IS REMOVED AS THE SYSTEM PULLS AWAY
SATURDAY AFTERNOON AROUND THE 18-19Z TIMEFRAME.

KAVL AND KHKY...FLIGHT CONDITIONS WILL REMAIN ABOVE IFR LEVELS AT
THESE LOCATIONS AS LOW LEVEL MOISTURE FLUX IS NOT AS SIGNIFICANT DUE
TO PROXIMITY TO PARENT SURFACE LOW.  HOWEVER...DID KEEP MENTION OF
MVFR CIGS AND -RA/RA WITH BR AHEAD OF INCREASING SURFACE WINDS.
WINDS WILL REMAIN NORTHERLY WITH NO SIGNIFICANT GUSTING EXPECTED
THROUGH THE PERIOD...HOWEVER CANNOT RULE OUT AN OCCASIONAL GUST.

OUTLOOK...CEILING AND VISIBILITY RESTRICTIONS WILL LINGER WELL INTO
SAT AS A SE COASTAL LOW PRESSURE SYSTEM PULLS SLOWLY AWAY. DRY HIGH
PRES WILL RETURN SUNDAY INTO MONDAY...WITH A FAIRLY WET FRONTAL
SYSTEM EXPECTED ON TUE.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-02Z
KCLT       HIGH  80%     MED   65%     HIGH  91%     HIGH  96%
KGSP       MED   66%     LOW   58%     HIGH  85%     HIGH 100%
KAVL       HIGH  88%     MED   68%     HIGH  81%     HIGH  92%
KHKY       HIGH  87%     MED   69%     MED   78%     MED   79%
KGMU       MED   64%     LOW   57%     HIGH  81%     HIGH  90%
KAND       MED   74%     LOW   56%     HIGH  82%     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...SBK
NEAR TERM...CDG/MCAVOY
SHORT TERM...WIMBERLEY
LONG TERM...LG
AVIATION...CDG






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