Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 181806

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
206 PM EDT Mon Sep 18 2017

High pressure will remain in control of the weather pattern across
northeast Georgia and the western Carolinas through much of the
week, leading to above normal temperatures and generally below
normal precipitation chances. Meanwhile, Hurricane Jose will remain
over the western Atlantic with no impacts expected across the
southern Appalachians and surrounding areas.


As of 145 PM: A narrow ridge will remain over the southern
Appalachians and vicinity through Tuesday. This will partially be
reinforced by Hurricane Jose as it continues to move north over
the open Atlantic, not far off the NC/VA coast. Within our CWFA,
a shallow unstable layer exists under the subsidence inversion
associated with that ridge, and this has allowed for abundant
cumulus growth. However short-term guidance indicates only isolated
showers developing, keying mainly on two areas: within a zone of
weak convergence just west of I-77, and in the northern mountains
and foothills. Afternoon PoPs have been revised accordingly. This
cloud cover should thin out by sunset leaving clearer skies for the
evening. Guidance consensus does indicate some low-level moisture
advection into the NC Piedmont in the early morning hours, as Jose
moves further north, which may reintroduce some cloud cover. Mins
will be in the mid 50s mountain valleys and lower to mid 60s over
most of the Piedmont.

The ridge will weaken a bit Tuesday as a shortwave moves into the
mid-upper Ohio Valley. With reduced subsidence, thermo profiles from
the models indicate deep convection is a bit more likely throughout
the CWFA. That said, with no significant forcing mechanisms, the
models do not spit out much QPF over the area overall, keeping
what they do produce over the mountains/foothills; PoPs reflect
this. Max temps will be a degree or so warmer than today, 1 to 2
categories above climo.


As of 200 AM EDT Monday: With Hurricane Jose drifting northward over
the offshore waters of the Mid-Atlantic on Tuesday, a shallow ridge
of high pressure will remain in place over the southern Appalachians
and surrounding areas. Any isolated afternoon shower coverage should
be similar to previous days late Tuesday, but with a slight increase
in thunder potential as lapse rates improve somewhat over the

A very weak mid-level trough will develop from the mid OH valley
across the Appalachian mountain chain on Wednesday, but with
generally westerly mid-level flow persisting over our region. 850 to
500 mb lapse rates should increase to 6.5 to 7.0 deg C across the NC
mountains for slightly better late day PoPs and thunder chances than
on Tuesday. Expect temperatures to be about one to two categories
above climatology through the short-term period, with Wednesday
afternoon likely featuring the warmest temperatures of the week.


As of 210 AM EDT Monday: Weak upper troughiness will extend
southwest from the offshore location of Jose near southern New
England to the central Gulf coast, while a prominent ridge wraps
over the top from the southern plains to the Midwest through the
Great Lakes. At low levels, flow may acquire a more easterly to
southeasterly component into the southern Appalachians late Thursday
through Friday. This could lead to more clouds, slightly cooler
temperatures (still above climo, though), and a steady uptick in
diurnally favored PoPs along the eastern side of the mountains
through late Friday.

Current indications are that Hurricane Maria will likely remain off
the southeast coast through next weekend. This track would keep our
region in a drier subsidence zone through the end of the long term
period, with temperatures remaining above climatology.


At KCLT and Elsewhere: High pressure will continue to be the
dominant weather feature for the region thru 18z Tue, and VFR will
prevail for the most part. Low VFR cumulus will be seen this aftn
and an isolated brief SHRA is not out of the question, though
too unlikely to include in TAFs. With reasonably good radiative
cooling tonight, moist sfc conditions will develop and some fog
is expected to develop in parts of the mtn valleys much as it did
early this morning. Less consistent signals are present for light
fog in the outlying areas of the NC Piedmont, and issues there
are expected to remain isolated. KAVL most likely will narrowly
escape IFR at daybreak; MVFR fog also is warranted at KHKY. More
diurnal cu will develop by late morning tomorrow. Winds will be
light and mainly northerly tonight, but will transition to more
SW flow around midday, at all sites except KAVL. In some cases the
variability will not settle down until after 18z, so the next TAF
set will better define the WSHFT timing.

Outlook: Isolated, mainly high terrain diurnal showers will
remain possible through early week, with better mountain shower
coverage building Wednesday through Friday. Morning mountain valley
fog/stratus are also expected each day.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High  97%
KGSP       High 100%     High 100%     High  97%     High  94%
KAVL       High 100%     High  97%     High  86%     High  92%
KHKY       High 100%     High 100%     Med   77%     High  94%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High  97%     High  91%

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:




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