Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 220238
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1038 PM EDT Mon Aug 21 2017

.SYNOPSIS...
Typical late summer conditions will persist ahead of an approaching
cold front, which will reach our area Wednesday. A large region of
surface high pressure will then gradually build into the area late
this week through the weekend, bringing unseasonably cool and dry
air.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 1040 PM EDT: Convection continues to wane late this evening,
with just a few showers persisting in upslope areas across the
western Upstate and the southwest NC mountains. These should
continue to dissipate overnight. Some patchy mountain valley fog is
likely overnight, but otherwise expect mainly thin cirrus with
minimum temperatures about 5 to 7 degrees above climatology.

On Tuesday, the upper ridge looks to weaken a bit as a trough
approaches from the west. With that, guidance favors convection
across the high terrain once again based on a diurnal trend, with
propagation into the foothills/piedmont possible late in the day.
Thus, solid chance pops were featured over the mtns, with slight
chances spread across the remainder of the fcst area.  Temperatures
through the period will remain a few degrees above normal.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
As of 2:30 PM EDT Monday: The trend Tuesday night will be to allow
diurnal convection to wane early in the evening. We will draw POPS
back to the NC/TN state line toward Wednesday morning ahead of a
slow moving cold front.

The combination of a surface cold front starting to impinge on our
region Wednesday, coupled with deep moisture, instability, upper
level energy and marginal shear, should support rather widespread
convection. We have most POPS in the high chance category or likely.

Because the upper level flow does not attain deep cyclonic flow at
our latitude, the front will start to stall Wednesday night (in a
west to east fashion). This will result in better POPS Wednesday
night edging south into NE Georgia and upstate SC.

The front then moves very slow slowly south, but does not get far
enough away to still impact our region with a chance of showers or
thunderstorms. The best chances will be located across our southern
upstate piedmont.

Another hot temperature day is expected Wednesday, particularly as
the H85 thermal structure increases ahead of the front. Thursday
should be noticeably cooler with the passage of the front.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 145 PM Monday: An upper level trough will persist over the
eastern part of our nation through the weekend and into early next
week. Some differential heating from terrain features in the
mountains along with low level easterly to southeasterly flow
against the mountains will assist in producing a bit of convection
each afternoon. Of course, upslope flow will be better according to
the orientation of the ridge lines with wind flow. As the center of
the high slowly shifts from the Great Lakes to New England, the low
level wind flow will shift from easterly to more SE. CAPE values
will be low with under 400 for the mountains each day. The next
significant shortwave will cross the Great Lakes early next week
with moisture building ahead of it.  There may also be a tropical
contribution to this moist flow as models show a tropical system
crossing the western Gulf and getting caught up in the overall flow.
This development will make some POP necessary at the end of this
forecast.

Temperatures will be around 5 degrees below normal over the weekend
then at the very least overnight lows will be a few degrees below
but with any additional moisture could be close to normal.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
At KCLT and Elsewhere: VFR conditions will generally continue
through the period, although mountain valley fog and low stratus
will be possible overnight, and a small chance of thunderstorms
could bring associated restrictions to KAVL Tuesday afternoon.
Otherwise, moisture will gradually increase over the region late in
the period tomorrow ahead of an approaching cold front, with surface
winds turning southwest and slowly increasing. Expect mainly VFR
cumulus with heating with bases at 4000 to 5000 feet Tuesday
afternoon.

Outlook: Chances for diurnal convection and morning mtn valley
fog/low stratus gradually increase during through midweek, with the
best chances expected Wednesday, as a cold front pushes into the
area. Chances for restrictions and diurnal convection should
diminish again Thursday into Friday.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High  96%     High 100%     High 100%
KGSP       High 100%     High  95%     High 100%     High 100%
KAVL       High  95%     Low   26%     High 100%     High 100%
KHKY       High 100%     Med   70%     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...DEO
NEAR TERM...CDG/HG
SHORT TERM...TS
LONG TERM...DEO
AVIATION...CDG/HG



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