Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 212124
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
524 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 500 PM EDT: The cumulus field and convective coverage took a
hit during the eclipse with the associated cooling, but it has
rebounded for much of the area since 330 pm. Still anticipate most
of the isolated to scattered convection to form along the eastern
slopes of the mountains and move very little through sunset before
dissipating. Given the warm temps aloft, very little of the activity
should be strong. Guidance continues to favor abundant BL moisture
across the region on Tuesday morning, with patchy fog possible for
any regions that experience convection this afternoon, yet with the
best chances in the mtn valleys as was the case this morning.
Moving into Tuesday, the upper ridge looks to weaken a bit as a trof
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 /22Z MONDAY THROUGH SATURDAY/...
At KCLT and Elsewhere: VFR through the period at all sites aside for
at KAVL where mtn valley fog is expected near daybreak on Tuesday.
Otherwise, deep ridging prevails across the region which should keep
convection at bay at most terminals, with sct shra expected over the
mtns this afternoon.  Therefore, did include vcsh at KAVL. All other
sites are dry with llv cu and current light/vrb flow veering
southerly almost immediately.  As stated, added fm group for IFR fog
at KAVL tomorrow morning, with all other sites remaining VFR through
the period.

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 may diminish
again during late week.

Confidence Table...

            21-03z        03-09Z        09-15Z        15-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High  94%     High 100%
KAVL       High 100%     High  94%     Med   64%     High 100%
KHKY       High 100%     High 100%     High  94%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  88%     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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