Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 251445
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1045 AM EDT Tue Apr 25 2017

.SYNOPSIS...
An area of low pressure will gradually weaken and drift northeast
along the Mid-Atlantic coast today through tonight. Warm and dry
high pressure will filter in behind the low through Wednesday. A
dissipating cold front crosses our region Thursday, then warm and
humid high pressure builds back in for Friday and Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1030 AM EDT, water vapor imagery shows the deep low pressure
circulation moving up the NC coast, while radar returns continue to
diminish over the piedmont of the Carolinas. Any isolated showers
going forward along or east of I-77 should be quite light early this
afternoon. The clouds are breaking up farther to the southwest over
NE GA and the western SC Upstate and temps may need a one degree
boost in those areas. Cannot completely rule out an isolated shower
developing back near the high terrain or Upstate in differential
heating given all the near surface moisture from the recent
rainfall, but with confidence too low to mention a PoP.

Ridging surface and aloft move in tonight. Light winds and clearing
skies will create good radiational conditions. This and lingering
low level moisture will lead to increased fog potential. Too early
to be sure, but areas of dense fog will be possible. Lows will be 5
to 10 degrees above normal.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 300 AM EDT Tuesday: Wednesday looks like a quiet, pleasant
day, as sfc high pressure builds in under an East Coast ridge. Any
fog or stratus should lift/scatter out by late morning, leaving
mostly sunny skies and a light southwest wind. Max temps are
expected to be 6 to 9 degrees above normal.

Wednesday night into Thursday, the upper ridge axis will shift, as a
negatively tilted short wave trough lifts up the eastern side of a
broad long wave trough covering 2/3rds of the CONUS. The short wave
looks to brush the NC mountains midday Thursday, but should be
accompanied by decent instability with a plume of moisture advecting
in from the SW. So PoPs ramp up to high-end CHC to likely in the
west, and low-end CHC east. The operational models are in agreement
on decent overlap of 40-50+ kts of 0-6 km shear and 1000-2000 J/kg
of sbCAPE just to our SW. So it will interesting to see how
convection evolves along and ahead of the trough. Temps will remain
about 5-10 degrees above normal.

Convection may linger east of the mountains well after sunset, as
25-35 kt SWLY LLJ continues advecting higher theta-e air into the
CWFA. Min temps will be about 8-12 deg above normal.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 300 AM EDT Tuesday: It is going to feel like summer this
weekend, as an upper ridge amplifies over the eastern CONUS, setting
up a strong Bermuda High pattern over the Southeast. Diurnally
driven convection is expected both Friday and Saturday with temps
well above normal. Saturday looks like the warmest day of the next
seven, where a few spots may hit 90 in the Piedmont.

Sunday and Monday, the broad long wave trough will begin to progress
across the central CONUS, with its axis entering the Ohio and
Tennessee Valley states by early Monday. An attendant cold front
looks to have plenty of moisture to work with, and may be strongly
forced as it approaches the Southern Appalachians. The 00z ECMWF has
come into good agreement with the GFS on the timing of the fropa
being in the 12z Monday to 00z Tuesday. The front looks to lose a
lot of its better buoyancy, as the best mid and upper support
remains in the cold air region behind the sfc front. Depending on
the speed of the front, it could provide a solid soaking rain. At
this point, it doesn`t look like QPF will be excessive. Temps will
be a category or two cooler than Saturday, but still above normal.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: Light showers and associated VSBY
restrictions have ended this morning. IFR ceilings will slowly
improve at KCLT, with MVFR for most of the afternoon. At the
foothill and mountain sites, any lingering MVFR layers will quickly
lift and scatter to VFR this afternoon, taking the longest to
improve at KHKY. W to NW winds continue through the day at the SC
sites then go light this evening. N to NW winds for the NC sites
before going light this evening. Expect at least MVFR fog to develop
overnight with the moist ground, light winds, and clear skies. KAVL
most likely to see IFR, so have included that there. May see dense
fog elsewhere by daybreak, but not certain enough for the TAF at
this time.

Outlook: Conditions should continue to improve through Wednesday as
dry air works in behind the departing low. Return flow moisture
ahead of the next system will develop late in the week.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       Med   73%     Med   76%     High 100%     High 100%
KGSP       High  80%     High 100%     High 100%     High 100%
KAVL       High  82%     High 100%     High 100%     Med   65%
KHKY       Med   77%     High  93%     High  95%     High  95%
KGMU       High  80%     High 100%     High 100%     High  95%
KAND       High  93%     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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...ARK
NEAR TERM...HG/RWH
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...HG/RWH



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