Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 240736
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
336 AM EDT Thu Aug 24 2017

.SYNOPSIS...
High pressure building in behind a cold front will introduce an
extended period of unseasonably cool conditions that is expected to
last through at least early next week. Although active tropical
weather is anticipated near the Southeast early next week, this is
unlikely to have any impact on the weather over our area for at
least the next 7 days.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 320 AM EDT Thursday: what`s left of a few small showers is
evident over the SE fringe of the fcst area. These cells should
die off very soon with the loss of sfc-based instability.

Otherwise, conditions remain quiet across the fcst area with drier
air working its way in from the north and the frontal bndy stubbornly
lingering just to our south. This front will continue to slowly move
southward today as an upper NE CONUS shortwave moves east and a dome
of sfc high pressure builds over the east central CONUS. This will
give generally light, northerly winds behind the front and lower
dewpoints. Dewpoints will likely decline by 5 to 10 degrees by this
evening. Instability diminishes as well, but a small area of roughly
500-1000 j/kg of MLCAPE will still be present over the Piedmont areas
this afternoon, however significant capping in the soundings and a
total lack of forcing should limit any significant convection. High
temps will also decline by about 4 to 8 degrees across the area and
remain below climatology into the weekend.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
As of 300 am Thursday: What would normally be considered as the dog
days of summer will feel nothing of the sort, as upper troughing
will persist along the East Coast through the short term (and into
the medium range), supporting expansive surface high pressure
covering much of the northeast quadrant of the country, supporting a
prolonged period of E/NE low level flow across our forecast area. In
fact, temps are forecast to trend down a couple of degrees each day
through the weekend, as inverted surface ridge gradually sharpens on
the east side of the Appalachians with movement of the surface high
into a more favorable location to support a cold air damming-like
regime. Despite the drier more stable air that will be in place
through the period, precipitation chances will be non-zero,
especially Saturday through Sunday, as inverted surface trough
develops on the west side of the Appalachians, while E/SE flow
supports an upslope component. 20-40 pops, mainly for showers, will
be advertised during this time, mainly across the western half of
the forecast area, with the highest chances advertised over the
mtns.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
As of 315 am Thursday:  From a model/ensemble consensus standpoint,
the medium range looks to be nothing more than a continuation of the
short term, with anomalously low upper heights, E/NE flow/
anomalously dry air persisting through at least Tuesday. Of course,
the potential horse-fly in the ointment will be the situation in the
tropics, as the Southeast will be sandwiched between a rejuvenated
tropical cyclone Harvey (somewhere in the vicinity of the Texas
coast) and another cyclone off of the Southeast coast. The global
models and ensemble systems are converging toward a strong consensus
regarding Harvey (at least through next Wednesday) that it will
plague the Texas coast for much of the first half of the week, with
very little/0 chance for impacts in our area through that time.

The western Atlantic cyclone may offer a bit more interest for our
neck of the woods, as the latest runs of the ECMWF, which present a
"closer-to-the-coast" solution, wrap tropical moisture into the
area on strong easterly flow north of the cyclone, suggesting a
potential upslope precip event at some point early/mid week. Again,
it`s the only model that`s doing this, and even if this were to
occur, there would be only a tight window of opportunity before
subsidence on the western periphery of the northeast-moving cyclone
took over. In terms of the sensible forecast, small (20-30) pops
will be advertised each day, while temps will generally remain 5-10
degrees below climo through the period.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
At KCLT and Elsewhere: expect VFR conditions thru the 6z TAF period
as cooler and drier Canadian high pressure spreads over the region
from the north. There is a slight chance KAVL could see some brief
visby restrictions early this morning, however it`s doubtful that
temps will drop low enough for fog to develop. Winds will remain out
of the north thru the overnight and morning and become more NELY
this afternoon at all sites except KAVL, which will shift to a more
NWLY direction. A moist layer in the 4 to 6kft range should keep bkn
to sct cloud decks over the fcst area thru the afternoon with clouds
thinning after that.

Outlook: drier air is expected to persist over the region thru Friday.
More moist profiles are expected to return to the region over the
weekend, increasing the chances for showers and thunderstorms and
flight restrictions.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High  93%     High  83%     High 100%     High 100%
KGSP       High 100%     High  98%     High 100%     High 100%
KAVL       High  86%     High  96%     High 100%     High 100%
KHKY       High 100%     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...JDL
NEAR TERM...JPT
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...JPT



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