Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 210731

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
331 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 245 AM EDT: KGSP radar shows a persistent patches of light to
moderate rain stretched across the I-85 corridor. Don`t be fooled by
the light returns...the rain is actually falling at a moderate clip
where the reflectivity is greater than about 30 dBZ owing to the
tropical nature...fortunately not so fast as to cause any problems
with flooding. Will tweak the precip probs to account for the
movement of the band.

Kind of a complicated, messy fcst over the next 24 hours in-between
where the circulation around T.S. Cindy ends and the rest of the
atmosphere begins. We find the wrn Carolinas stuck 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 today. 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 significant
flooding. Thus, we will not issue any watches at this time. As we
work through the afternoon and into the 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 Mtns. 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: Expect flight conditions to deteriorate as
the very high amount of low level moisture will lend itself to the
formation of an IFR/LIFR stratus deck. Meanwhile, patches of
tropical rain will occasionally reduce vis into the MVFR/IFR range
as well, at least through daybreak. Thereafter, expect the precip to
taper off a bit and with that the boundary layer should warm and
lift the low cloud ceiling into the MVFR range. Wind should come
around to S/SW during the day at all taf sites. Expect sky to have
multiple cloud decks today, the lowest of which should form an MVFR
ceiling in most places for the balance of the day. Additional precip
may develop just about anywhere at any time, so have just left a
VCSH in place and we will amend from there. The lowest cloud deck
should lift to VFR in the mid/late afternoon as some dry air
attempts to move in.

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. And uptick in diurnal convection and
associated restrictions can be expected, as well as potential for
morning fog/low stratus.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
KCLT       High  84%     High  87%     High  91%     High 100%
KGSP       High  90%     Med   77%     High  91%     High 100%
KAVL       High  81%     High  96%     High 100%     High  89%
KHKY       High  86%     High  82%     High 100%     High 100%
KGMU       Med   68%     High  81%     High  92%     High 100%
KAND       High  80%     High  80%     Med   78%     High  88%

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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