Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 211451

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1051 AM EDT Wed Jun 21 2017

A remnant frontal boundary will linger over the area today, as
Tropical Storm Cindy approaches the Louisiana coast. As Cindy lifts
north into extreme western Louisiana, tropical moisture spreads
across the region Thursday and Friday.  A cold front approaches the
area Sunday and moves through the area early next week with drier
weather to follow.


As of 1040 AM EDT: Measurable precipitation has generally pared back
to the escarpment of the southern mountains late this morning in the
best area of upper divergence and lingering low level convergence
and upslope flow. PoPs have been increased in this area and
generally decreased across much of the rest of the forecast area.

Otherwise, T.S. Cindy moisture will play a role in the eventual
weather across the western Carolinas and northeast Georgia starting
as early as tonight. The region remains under an axis of dilatation
brought about by the outer edge of the circulation around T.S.
Cindy, the Atlantic subtropical ridge, the large warm anticyclone
over the desert SW, and a broad upper trof in the nrn stream. This
will keep a swath of sheared out vorticity overhead along with weak
frontogenesis, which should act upon a plume of deep tropical
moisture fed by the circulation around Cindy to produce scattered
mainly light showers across at least the srn half of the fcst area
this afternoon, with a focus on the souther mountains. Cannot rule
out some moderate rain rates with fairly high PW and deep warm cloud
depth allowing for warm rain processes to dominate, but think at
this point the forcing and instability are not great enough to
result in any flooding. Thus, no watches are warranted at present.
By evening, a slow evolution/movement of all the players will
gradually shift/pivot the axis of dilatation allowing some dry air
to filter in from the NE. Frontogenesis weakens, but the building
subtropical ridge will allow low level flow to veer a bit and
improve the upslope flow into the mtns. As a result, precip
probability gradually drops over the wrn Piedmont of NC/metro CLT,
but gradually rises over the NC mtns, especially over the Nantahala
area and northeast GA. Temps will remain about 5 deg below normal
again today, but continued mild overnight tonight.


As of 300 AM EDT Wednesday: the remnants of T.S. Cindy is expected
to drift north roughly along the TX/LA border on Thursday, while a
subtropical ridge reasserts itself into the Carolinas. This will
increase deep-layer SWLY flow atop the CWFA between the two systems.
This flow will bring tropical moisture into the area, with PWATS
likely between 2 to 2.5" by Thursday evening. Guidance hints at
increased lift ejecting from Cindy`s circulation with a vort max and
upper jetlet. So PoPs ramp up to likely west and high-end chance
east. A heavy rain/localized flood threat will probably exist
Thursday night, especially in the SW-facing slopes of the southern
Appalachians. But overall, the biggest heavy rain threat looks to
stay west of the area. Max temps will be below normal and min temps
above normal within the very moist air mass.

On Friday, guidance generally agrees that the subtropical ridge to
our east will bring slightly drier air and less upper support for
precip. However, temps will rebound to near normal with still plenty
of humidity. So perhaps a bit more typical late June diurnal
convection can be expected, although severe threat should stay low.
The axis of heaviest rain associated with remnants of Cindy should
stay west of the area on Friday.


As of 330 AM EDT Wednesday: a northern stream trough will dig
slightly into the Midwest on Saturday and should absorb the remnants
of T.S. Cindy. An associated cold front will cross the Ohio Valley
and be roughly along the Appalachians on Saturday. Both the GFS and
ECMWF try to keep a compact remnant circulation along the front,
crossing it over western NC during the day on Saturday. This will
definitely enhance low-level shear. Assuming there is decent CAPE
with not too much cloud cover, the Piedmont may have a non-zero
tornado threat (or at least a severe wind threat). The front will
have elevated PWATS due to the tropical interaction, but should be
moving along enough to limit a more widespread heavy rain threat.
Temps will be tricky on Saturday, depending on the timing of the
front`s arrival. But will go with near to slightly above normal.

The front will stall out across the Deep South to central Carolinas
Sunday and Monday. A mild continental air mass will settle in across
the Mid-South and some of this dry air will begin to filter in atop
the CWFA. So the end of the medium range features dropping dewpts
and lower PoPs. Temps will be near normal, with possibly below
normal min temps due to the dry air.


At KCLT and elsewhere: Slow lifting and scattering of the IFR clouds
is occurring this morning with very limited coverage of rain or
showers. KAVL should be the last location to recover above IFR
through Noon as light showers continue there. Should also see
slightly faster recovery to VFR through the afternoon across the
foothills and piedmont in light of the weaker coverage, but some
MVFR bases remain possible at times with heating of the moist
boundary layer. Winds should remain S/SW during the period at all
taf sites. Precip becomes more likely over the mountains and around
KAVL through late day as upslope flow becomes more established.
Eventually, this may result in a steadier rains moving back into the
region from the southwest overnight, along with associated IFR

Outlook: Moisture continues across the area through the end of the
week, enhanced by remnants of Tropical Storm Cindy that will
approach late in the week. An uptick in diurnal convection and
associated restrictions can be expected, as well as potential for
morning fog/low stratus.

Confidence Table...

            15-21Z        21-03Z        03-09Z        09-12Z
KCLT       Med   73%     High 100%     High 100%     High 100%
KGSP       Med   71%     High 100%     High 100%     High  87%
KAVL       Med   79%     High 100%     High  88%     Med   74%
KHKY       High  96%     High 100%     High 100%     High  90%
KGMU       Med   71%     High 100%     High 100%     High  84%
KAND       High  81%     Med   73%     Med   71%     Med   78%

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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