Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201448

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1048 AM EDT Wed Sep 20 2017

A weak trough crossing the region today will settle along the
southeast coastline Thursday through Friday. A gradual increase in
easterly flow moisture is likely through the latter part of the
week. Drier and stronger high pressure will settle over the region
during the weekend, and likely persist through early next week, as
both Jose and Maria remain off the east coast.


As of 1030 AM: The synoptic pattern overall is rather similar to
days past as broad ridging dominates across the east, and troffing
prevails out west. A difference, however, is the presence of a
shortwave trough now centered over West Virginia. Lobes of vorticity
will round this shortwave and pass thru the CWFA this aftn, which is
of interest as a potential initiation mechanism for diurnal showers
and t-storms. Convective cloud temp from the morning GSO RAOB is
83F which should be reached in areas of the lower Piedmont by noon
or 1 PM. Hence, it looks reasonable to buy into the latest HRRR,
which shows initation southeast of I-85, with a secondary round
firing over the Blue Ridge.  Any convection that fires over the
mtns may propagate eastward into the foothills/piedmont regions
to some extent by late afternoon, perhaps aided by a vort lobe.
Profiles today do exhibit slight CIN, however deep dry air
supports modest lapse rates and abundant instability above the
cap, upwards of 1500 J/kg albeit with very weak shear. Although
general thunderstorms still will predominate, wouldn`t be suprised
to see a handful produce damaging wind or even hail in light of
the dry profiles.  Convection will wane diurnally.  Temps today
will be quite warm given that we`re nearing the first day of fall;
highs top out nearly 6-8 degrees above normal.


As of 300 AM EDT Wednesday: An upper level trough axis will settle
along the southeast coastline Thursday through Friday, as a 590 dm
ridge axis sets up from the Great Lakes to the MS Valley. Low level
easterly flow developing Thursday afternoon through Friday should
help to focus the highest chance PoPs along the eastern slopes of
the mountains. Thus anticipate mainly diurnal, scattered ridge
top/eastern mountain convection both Thursday and Friday afternoons
with weak forcing and limited moisture. SBCAPE values should
steadily recover to 1000 to 1500 J/kg to support a scattered thunder
mention. Minimum temperatures will remain warm - some 8 to 10
degrees above climo. Max Temps will be one to two categories above
climo on Thursday and a touch cooler on Friday.


As of 300 AM EDT Wednesday: The upper ridge will strengthen from the
north through the weekend as Tropical System Jose meanders off the
mid-Atlantic coast and Hurricane Maria moves northward well east of
coastal FL/GA. Much drier air will wrap southward from the ridge,
with very limited precipitation chances - mainly just isolated
showers Saturday afternoon in far southwest mountain sections.

The consensus solutions keep Maria far enough east off the Carolina
coast Monday through Tuesday to have no impact on sensible weather
across our forecast area. There are vast differences in the handling
of the Jose remnants that get absorbed into the Maria circulation,
but even the members with inland impacts from Jose keep any
associated moisture over the mid-Atlantic coastal region and north
of our area through Tuesday. Thus expect mostly northerly flow
around the offshore systems and generally dry conditions with
continued temperatures above climo.


At KCLT and Elsewhere:  VFR through the period at all sites aside
for the possibility of tsra induced MVFR, as well as Thursday
morning fog/visb restrictions at KAVL.  Otherwise, light/vrb flow
will prevail amidst mid/upper level clouds through late morning
with flow gradually becoming more sly.  Llv cu is expected to
dominate through the mid/late part of the day as convective
trends increase westward across the high terrain.  With that,
tafs now feature VCTS at KAVL/KHKY, with prob30s favored at the
remaining sites given slightly later toa per CAMS.  Beyond that,
any remaining low stratus/cu will gradually sct into the overnight
hours leading to another night of fog potential.

Outlook: Chances for diurnally favored showers and thunderstorms
will continue to increase as the week progresses, with the best
chances for overall coverage being on Thursday and Friday as flow
veers easterly and marginal moisture advection returns across the
region.  Chances for restrictions from early morning fog across
the northern NC Piedmont and foothills, as well as in the mtn
valleys will also be a concern. Drier weather appears to return
for the weekend.

Confidence Table...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 100%     High  86%
KHKY       High  88%     High 100%     High 100%     High  95%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High  95%

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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