Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 182019
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
419 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 415 PM EDT FRIDAY...PRECIPITATION SHIELD CONTINUES TO MARCH
NORTHWARD FROM THE PARENT DISTURBANCE IN THE NORTHEASTERN GULF OF
MEXICO...THEREFORE DECIDED TO GO AHEAD AND RAMP POPS UP ALONG/SOUTH
OF THE I85 CORRIDOR.  TEMPERATURES ACROSS THE REGION ARE HOLDING IN
THE MID TO UPPER 50S AMIDST LIGHT/MODERATE NORTHEAST WINDS AND
OVERCAST SKIES.  ADJUSTED TEMPERATURES AND DEWPOINTS TO REFLECT
LATEST OBSERVATIONS AND LEFT THE REMAINDER OF THE FORECAST AS IS
WITH THIS UPDATE.

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 VWPS 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 DOESN/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 /20Z FRIDAY THROUGH WEDNESDAY/...
AT KCLT...EVEN THOUGH THERE HAS BEEN A HIGH OVERCAST ALL DAY...THE
LOWER CIGS CAN/T BECOME ESTABLISHED IN THE DRY LLVL AIRMASS. THIS
WILL SOON CHANGE AS WIDESPREAD LIGHT TO MODERATE RAIN WILL MOVE IN
FROM THE SOUTH AROUND 2100 UTC. CIGS SHOULD SLOWLY FALL...WITH IFR
CONDITIONS EXPECTED TO DEVELOP BY AROUND MIDNIGHT. WITH DEEP
EASTERLY FLOW...IFR CIGS ARE EXPECTED TO LAST INTO TOMORROW AFTN. A
PERIOD OF MODERATE TO HEAVY RAIN WILL FALL OVERNIGHT...WITH PCPN
BECOMING LIGHTER BY MID-MORNING ON SATURDAY. WINDS WILL BECOME GUSTY
OUT OF THE NE BY LATE EVENING AS LOW PRESSURE DEEPENS OVER THE NRN
FLORIDA.

ELSEWHERE...THE REST OF THE FOOTHILLS AND PIEDMONT WILL GENERALLY
SEE SIMILAR CIG...VSBY AND PCPN TRENDS AS AT KCLT. THE PCPN WILL
START A LITTLE EARLIER OVER THE UPSTATE AND LATER AT KHKY. CIGS
SHOULD TAKE SEVERAL HOURS LONGER TO FALL INTO THE IFR RANGE AT KHKY
THAN ACROSS THE REST OF THE REGION. SOME OF THE GUIDANCE HAS WINDS
NE WINDS GUSTING UP TO 30KTS OVER THE UPSTATE AFTER SUNRISE ON
SATURDAY.

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...

            20-02Z        02-08Z        08-14Z        14-20Z
KCLT       HIGH 100%     MED   63%     MED   72%     HIGH  82%
KGSP       HIGH  94%     MED   63%     HIGH  81%     MED   68%
KAVL       HIGH 100%     MED   71%     MED   71%     MED   67%
KHKY       HIGH 100%     MED   75%     MED   65%     MED   65%
KGMU       HIGH  94%     MED   60%     MED   78%     MED   67%
KAND       MED   79%     MED   70%     MED   79%     HIGH  97%

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...MCAVOY






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