Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 211440
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1040 AM EDT SUN AUG 21 2016

.SYNOPSIS...
A cold front will push through the area from the northwest this
evening and tonight. High pressure will build in behind the front
Monday,  bringing cooler and drier air to the area for most of the
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1035 AM EDT Sunday: The first round of showers is moving
across the mountains at this time. Expect these showers to dissipate
and move east through the morning as additional convection to the
west moves in and redevelops across the mountains. Mid level winds
are stronger than previous days as a short wave moves into the area.
This is creating effective bulk shear in the 30 knot range just to
our west which is forecast to rotate across NC this afternoon. 12Z
observed RAOBS show moderate instability developing with the
forecast temps and dew points. However, DCAPE values will be modest,
with highest values south of I-85. The soundings are also very moist
with PW values near 2 inches and little to no mid level dry air.
These features would suggest heavy rain to be a greater threat than
severe thunderstorms. However, steering flow is relatively high for
this time of year resulting in good storm movement and limiting the
flood threat. Also, with the stronger mid and low level winds, the
combination of shear and instability could lead to isolated severe
downbursts.

As a cold front passes across the mountains, it will break up
somewhat as the upper dynamics continue to lift northeast with the
surface low. Additionally, downslope drying will also affect the
integrity of the front. As it pushes east, convection chances will
be lower across southeastern zones.

Expect highs today a couple of degrees below seasonal normals, but
the real effect of the front will be felt tonight, with overnight
lows expected 4-5 degrees cooler than what we`ll see this morning as
the cooler and especially drier air advects in starting just before
midnight in the mountains and spreading across the area through
daybreak.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 AM EDT Sunday...An upper ridge will build back in across
the Southeast states for Monday and Tuesday, providing subsidence
and mid-level warming to cap any convective chances. To help keep
things stable, a nice, late summer dry-ish air mass will settle in
across the region from the NW. Surface high pressure will slowly
drift east from the Ohio Valley to the Mid-Atlantic by late Tuesday.
Temps will be near or slightly below normal with noticeably less
humidity than we have seen in a while, as dew points drop into the
50s and  60s.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 315 AM EDT Sunday...The 00z cycle of guidance continues to
trend drier for the latter half of the week, as upper ridging holds
on across the eastern CONUS thru the end of the week. The low-level
flow will briefly turn around out of the SE on Wednesday, as high
pressure drifts off the Mid-Atlantic coast. This may result in
enough moisture and shallow instability coming off the Atlantic for
some isolated showers in the afternoon across the SW NC mountains and
adjacent mountains/foothills of NE GA and SC. But overall, Wednesday
looks dry with temps near normal.

Thursday thru Saturday, temps gradually return to slightly above
normal, as the upper ridge dominates. A cold front will approach
from the west, but basically washes out as it tries to push into the
forecast area. The GFS still shows some weak QPF response in the
high terrain each of the three days, but the 00z ECMWF is dry. So
PoPs were knocked down slightly with this forecast package, and may
still be overdone, if the current trends hold.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Low clouds have scattered out, but a brief
MVFR cig cannot be ruled out as heating helps CU to develop in the
moist air mass. Bases should lift to low VFR through the day. As a
cold front approaches, an increase in convection is expected between
16-18z. Have carried VCTS in all but KCLT, with TEMPO -TSRA
everywhere, starting earlier at western sites. SW winds to start the
period will pick up ahead of the front later this morning with some
low-end gusts possible. Front pushes in this evening swinging winds
around, and current timing for NW winds at KCLT at 01z. Much drier
air moves in overnight though will likely see some fog and possibly
low stratus in the mountain valleys and KAVL before the drier air
moves in.

Outlook: Much drier air will filter into the area behind the front
Monday, resulting in fair weather through at least mid-week.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High  83%
KHKY       High  98%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     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...RWH/TDP
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...RWH/TDP



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