Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 210715

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
315 AM EDT Fri Sep 21 2018

High pressure will weaken and move east of the area through
Saturday. A weak, yet moist, cold front will then advance from the
north Sunday before moving back north on Tuesday. A stronger cold
front is forecast to push into the forecast area on Wednesday.


As of 230 AM EDT Friday: Quiet across the fcst area, but with
an expanding area of high-based stratocu covering much of the
NC portion. This may inhibit fog development thru
least the guidance thinks so. Will continue to monitor. Temps were
adjusted to agree with obs trend.

A large upper anticyclone/ridge centered over the Carolinas this
morning will gradually get pushed offshore and flattened through
tonight as a strong short wave trof traverses the upper Midwest and
Great Lakes regions. This wave will help to push a cold front toward
the region, but the front is expected to get strung out across
the Ohio Valley region. As a result, no significant changes are
expected to our weather today as deep convection should continue to
be suppressed by warm air aloft. Only the differential heating over
the ridgetops will be able to overcome the convective inhibition, so
we will retain the precip chances over the high elevations. Thunder
is not very likely, and severe weather chances are practically
nil. This activity should draw to a close with sunset, with more
fair weather thru Friday night. Temps will be seasonally warm.


As of 200 AM EDT Friday: The short range pattern over the weekend
remains rather progressive as a cold front advances toward the FA
Sat and then a moist wedge builds in Sun. The atmos will remain
quite moist and warm in the llvls Sat which will allow for mtn/top
convg -shra/tstms. Not expecting anything outside of general thunder
with these storms as an ulvl ridge remain in control and warms the
mlvls. A strong cP sfc high will build quickly east across the
Glakes region Sat night and begin ridging down east of the Apps thru
the morning. By midday Sun...the wedge bndry shud be located near
the SC/NC line and good sfc convg will allow for some stronger tstms
developing along a line from Hendersonville toward Monroe. The
timing with the exact placement of the sfc bndry will likely change
     but Sun afternoon and evening could see more widespread activity
across the NC zones. Temps will remain abv normal by a couple cats
Sat in continued s/ly flow. On Sun...expect a drop off in max temps
with increased cloudiness and an airmass mix across the ne/rn
portion of the FA...while the Upstate and NE Ga remain a little abv


As of 225 AM EDT Friday: Not too many changes were made to the
going fcst. The op models are in decent agreement with a moist wedge
persisting across the FA Mon into Tue before a cold front pushes in
Wed and becomes stationary as it encounters strong Atl ridging. This
shud lead to active weather with sct showers and tstms most locales
early on becoming more widespread by Wed. So...have maintained low
chance PoPs into Tue with higher end chances beginning Wed. The
atmos will be rather stable early in the period...but conditional
moderate instability will likely be realized Wed with the llvl convg
zone pushing in. So...some stronger and deeper convec cells are
possible into Thu. Max temps will begin the period below normal in a
moist llvl wedge and slowly modify to arnd normal thru the week.


At KCLT and elsewhere: The big question will be the development
of fog in the pre-dawn hours. Satellite imagery shows an expanding
area of high-based stratocu with cloud bases around 060. This could
very well inhibit fog development and the guidance has picked up on
that notion. So, have cut back on fog with this issuance and will
amend if we manage to clear off. Instead, most sites get a light
S wind. Still see a good chance of MVFR/IFR vis at KAVL, whereas
KCLT will be given a temporary MVFR ceiling around daybreak based
on the stratocu field developing upwind. After sunrise, expect
VFR conditions for the rest of the period with a S/SW wind. Deep
convection should be tied to the ridgetops this afternoon, thus
only a VCSH was included at KAVL.

Outlook: Anticipate diurnal showers and thunderstorms to become more
widespread this weekend with possible brief restrictions. Otherwise,
expect VFR conditions with the exception of possible overnight and
early morning fog focused predominately across the mountain valleys.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High  98%     High  81%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High  86%     High  96%     High 100%     High  95%
KHKY       High  95%     High  82%     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:




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