Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 220734

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
334 AM EDT Thu Jun 22 2017

Cindy will drift north across extreme western Louisiana today,
spreading tropical moisture across the region through tonight. A
cold front approaches the area Friday and pushes into the area early
Saturday, before crossing to the Atlantic coast Sunday through
Monday. Cooler and drier weather follows behind the front for the
middle of next week.


As of 315 AM EDT: A large area of light rain was gradually expanding
and invading the Upstate from northeast GA and will continue to do
so through daybreak. This will require further upward adjustments to
the precip probability, mainly over the srn mtns of NC and wrn

The next 12-24 hrs look relatively wet across the region as the
model guidance agrees that upper divergence and DPVA will gradually
improve through the day and continue through the evening, while low
level S/SW flow also improves. All this forcing will act upon the
persistent deep tropical moisture plume to produce a very good
chance of precip, ramping up through the day and remaining high
through late tonight, before starting to taper downward toward
daybreak Friday as forcing weakens temporarily. The fcst will
continue to feature a precip probability rising into the likely
range over the mtns/foothills today, with categorical tonight near
the Blue Ridge Escarpment where forcing maximizes. Prob will be
limited to the chance range over the ern zones away from the better
mechanical lift. Precip amts at this time do not appear to be great
enuf to raise flooding concerns over the mtns, so a watch is not
anticipated at this time. Severe storms appear unlikely with the
poor lapse rates and weak sfc-based CAPE. Have limited thunder to
the srn zones. Temps will be cool, but not as cool as the prev fcst
had, based on recent experience, so the high temp was nudged upward
a few degrees today. Temps will remain mild overnight again.


As of 300 AM EDT Thursday: the remnants of T.S. Cindy will begin to
be picked up by a northern stream trough over the Midsouth on
Friday. Meanwhile, the western edge of a large subtropical ridge
will build slightly westward into the Carolinas. This will advect
some slightly drier air and keep weak mid-level lapse rates atop the
CWFA. Guidance is in pretty good agreement on the deepest moisture
associated with Cindy staying west of the area thru the day, while
piedmont, in particular remains largely capped. So PoPs were trimmed
back, esp in the east. Bulk shear will increase thru the day, and if
we manage to get enough CAPE, could see at least a few strong to
severe storms. The CAMS that go thru Friday do show some multicell
segments with convection across the TN Valley. Some of this activity
will try to move into the NC mountains Friday evening. Temps will
rebound with more sunshine and influence from upper ridge to near
normal, making for a muggy day.

Friday night, the models agree that the remnant vort max associated
with Cindy will likely track across the Central Appalachians
overnight thru Saturday morning. This will bring a trailing vort
lobe and associated sfc front across the CWFA. This front should
have good moisture and forcing to work with. But model guidance is
not excited with instability and QPF response. So PoPs will range
from categorical along the TN border to mid-chc to the southeast.
The NC mountains could pick up some decent rain, but unless they get
a lot of rain Thursday, I don`t think there will be much of a flood
threat. Temps will remain above normal.

Saturday thru Saturday night, with the models trending faster with
the front and upper wave, the bulk of the afternoon convection may
be mostly east of the area. Have trimmed PoPs back and start drying
things out in the west by early Saturday evening. With that said,
bulk shear still looks decent for late June, and if the front ends
up being slower and there is better overlap of CAPE, there may be
some severe storms across the area. Highs are still tricky due to
the fropa, but guidance shows little change in thicknesses, so
expect near or slightly above normal temps.


As of 330 AM EDT Thursday: the medium range looks really nice and
pleasant for the forecast area, as a long wave trough persists
across the Great Lakes and digs into the TN Valley thru the middle
of next week. At the surface, a continental high pressure system
will gradually slide southeast across the Midwest Sunday-Monday and
settle over the southern Appalachians by Wednesday. Given the
gradual drying over the first couple days of the medium range, some
slight chc to low-end chc PoPs will linger, but expect basically dry
conditions for Tuesday and Wednesday. Temps will be as much as 5-8
deg below normal, coolest Tuesday thru Tuesday night. Dewpts will
fall into the 50s, which will feel nice after the humid conditions
we`ve had the last few days.


At KCLT: VFR for the time being, but is expected to change.
Substantial low level moisture remains in place, and the slightest
bit of upslope flow should force the development of a low cloud
ceiling. The guidance indicates this will happen starting around 09Z
and I tend to agree. If the weak upslope doesn`t do it, the arrival
of light precip from the SW will help do the trick. Note that an IFR
ceiling has developed at KCAE, which I take as an indication of what
will happen in the pre-dawn hours. Expect an MVFR/IFR stratus deck
to develop nwd over the airfield around the start of operations this
morning. Kept the IFR in a TEMPO group for now, until we see the IFR
start to expand. Wind will be light S or SW. Indications are that
light precip will break up in the mid morning, allowing the ceiling
to rise to VFR for the better part of the day, but suspect at least
through midday we will have some MVFR in the area. Guidance suggests
shower redevelopment in the afternoon/early eve so a PROB30 was
included. Confidence low after sunset across the Piedmont, so fcst
was left VFR with a light S wind.

Elsewhere: light precip will invade from the SW early this morning,
helping to bring a low cloud ceiling restriction. Think this will be
mainly MVFR with some temporary IFR over upstate SC, but will not be
surprised to see a long period of mainly IFR through daybreak. The
ceiling restriction should hold on through midday before the
boundary layer deepens enuf to bring the cloud base above 030 and
lower clouds scatter out. The guidance suggests this evening that
upslope flow will develop another ceiling at least as low as the low
end of MVFR, along with light rain. This was generally accepted, but
will not include IFR at this time.

Outlook: Abundant moisture will remain over the area through
Saturday, enhanced by remnants of Cindy which will approach from the
west on Saturday. An uptick in diurnal convection and associated
restrictions can be expected, as well as the potential for morning
fog/low stratus. Some drying may occur on Sunday.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High  83%     Med   68%     High  91%     High  88%
KGSP       High  81%     High  81%     High  88%     Med   77%
KAVL       High  94%     Low   59%     Med   74%     High  94%
KHKY       High  81%     Med   67%     High  83%     High  86%
KGMU       Med   74%     Med   79%     High  84%     High  81%
KAND       Med   72%     Med   68%     Med   77%     High  89%

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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