Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 211107

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
707 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 645 AM EDT: KGSP radar shows a persistent patches of light to
moderate rain moving NE across the region, with a larger area of
light rain over the SC Midlands. Will tweak the precip probs to
account for the movement of the precip bands.

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 be tenuous across
the CLT metro area for the early- to mid-morning hours as abundant
low level moisture will allow showers to form at any time and a low
cloud IFR/LIFR ceiling will persist. 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 remain
S/SW during the period 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 late morning/early afternoon.
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. Precip becomes less likely at KCLT
late in the day but more likely over the rest of the fcst area as
upslope flow becomes more established. Eventually, this may result
in a steady light rain in the early morning hours, bringing
conditions back down to MVFR and 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. And uptick in diurnal convection and
associated restrictions can be expected, as well as potential for
morning fog/low stratus.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       High  83%     Med   75%     High 100%     High 100%
KGSP       High  89%     Med   65%     High 100%     High 100%
KAVL       High  83%     High  95%     High 100%     High  83%
KHKY       High  83%     High 100%     High 100%     High 100%
KGMU       High  89%     Med   65%     High 100%     High 100%
KAND       Med   78%     High  90%     High 100%     Low   56%

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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