Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 181731

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
131 PM EDT Fri Aug 18 2017

A weak cold front will drop into the area tonight, but with
some drying expected over the weekend as the front sags south. The
front will stall just south of the area early next week, but the
warm and moist airmass will remain in place. Another front will
approach the area by mid-week.


As of 130 PM: Convection developing over the mountains as the weak
frontal boundary moves in. These showers and associated boundary
will only slowly move into the mountains through early afternoon.
The boundary then jumps into the developing lee trough by mid
afternoon and slowly moves east into early evening. Latest guidance
still suggests the best convective coverage will be across NC and
the eastern Upstate. These locations also have the best chance of
seeing any strong to severe storms. The 12Z GSO RAOB had an observed
surface based CAPE of 2000 J/kg. There was also a slight uptick in
bulk shear, although still relatively weak. This area will also see
the best upper divergence with the passing jet streak. Have updated
PoP forecast to show these trends. Still cannot rule out a strong or
severe storm across NE GA or the western Upstate, just that chances
are lower there. High temps and dew point forecast looks on track
with heat index values rising above 100 but remaining below 105
across portions of the CWFA.

Convection will diminish through the evening as drier/more stable
air filters into the region in the wake of the front. After another
day of above-normal maxes, the slightly drier air should allow
tonight`s mins to drip closer to climo.


As of 210 AM Friday: A strong s/w trof will cross the ern CONUS thru
the period. The best energy will remain well to the north of the FA
however as a sub/trop high noses into the SE region. Soundings show
a good amount of deep subs developing Sat persisting thru the day
Sun as the sub/trop ridge couples with a Canadian sfc high. Low
level moisture and flow will be meager...yet enuf for the
development of few/sct Cu. It will be hard to get much going
convec-wise each afternoon with overall neg forcing and mlvl warming
off-setting good llvl LRs. There may be some areas that break the
cap and a few deeper -shra or tstms could be locally possible.
Yet...think the best chance for -shra/tstms will be across the nrn
mtns due to mtn top convg near the passing h5 trof axis...and
perhaps across the far srn zones in proximity of a lingering broad
sfc trof. A subtle drying trend was made to the PoP grids mainly on
Sat. Max/min temps will be able to reach a cat or so above normal in
this environ.


As of 240 AM Friday: Not too many changes were made to the going
fcst. Mon still looks to be firmly under the control of a strong
sub/trop ridge with little flow thru the layer. This will create
strong sub and hold a 1021 mb sfc high off the Carolina coast.
Meanwhile...a sfc bndry will remain trapped to the south of the
fcst area. The models continue to show a slow northward progression
with the moist llvl convg zone and in fact fire up some convec
across the Midlands and cent GA arnd 16z. Soundings over the Upstate
however show little in the way of convec potential and mainly
few/sct Cu leading up to the solar eclipse. There could be some
moist adv into the area from any eventual storms to the south...but
the flow is so weak that it would likely take until the later
afternoon for increased mid/high level clouds to materialize over
the FA. The depth and coverage of these advective clouds is still
fairly uncertain attm and a lot will depend on the strength and
placement of the Atl ridge by Mon morning. Suffice to say...the fcst
will remain on the optimistic side as far as good viewing conds for
the mid day eclipse.

Otherwise...the deeper afternoon convec will remain mostly limited
across NC mtns Mon afternoon and again on Tue with some isol non/mtn
storms developing in strong thermals. A little better non/mtn
coverage may be had Tue/Wed afternoon as a pre/frontal trof works
in and stalls just east of the escarpment. Late Wed into Thu could
be rather active as deep layered shear increases ahead of a frontal
zone and the pre/frontal airmass becomes quite unstable. Continued
warm and muggy conds will continue thru the period with perhaps some
lower theta/e air mixing in by Thu afternoon/evening.


At KCLT and elsewhere: Convection developing across the mountains as
a weak cold front moves in from the west. CAM guidance has
consistently shown the best chances at KAVL and KHKY through mid
afternoon, then at KCLT from late afternoon into early evening. Have
TEMPO in these locations. Lesser chance at the SC sites, but still
good enough for VCTS. Convection ends by early evening as the front
moves east of the area. Although winds will shift from SW to NW then
N behind the front, drier low level air will be slower to fill in.
Still some question about fog or low cloud restrictions overnight.
Have gone with MVFR at KAVL for now as all guidance agrees on some
restrictions there. KHKY the next best chance, but confidence too
low to include for now. Winds turn N to NE for Saturday morning with
some Cu developing in the lingering low level moisture.

Outlook: Drier air is expected to result in an inactive weekend,
with very little chance of diurnal convection, and probably only
patchy early AM mtn valley fog/low stratus Sunday. A more typical
late summer pattern returns next week, with isolated/ scattered
afternoon/evening storms expected, along with better chances for
patchy fog/low stratus, especially in the mtn valleys.

Confidence Table...

            17-23Z        23-05Z        05-11Z        11-12Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     Med   75%     High  93%
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%     Med   75%

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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