Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 170513

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
113 AM EDT Mon Oct 17 2016

A low level ridge of high pressure will remain over the region, with
drier ridging building in aloft through at least the middle of the
week and temperatures rising to well above normal. Moisture and rain
chances will return by the end of the work week as a cold front
approaches the area.


0515 UTC Update: Sky cover was reduced per infrared satellite
imagery. Winds were updated with a blend of the latest NAM and
ADJMAV. Areas of daybreak fog were adjusted from a model blend.

As of 1015 PM Sunday: Overall really quiet through the near term
with upper high over Texas ridging toward the Southeast, with
corresponding surface high centered over the Carolinas. Only changes
at this time are minor changes to temps and dewpts overnight;
the previous fcst temps are already slightly below most guidance,
which seems appropriate given the pattern and trends so far. Patchy
fog will develop in the early AM, with the expectation of steady
and relatively high dewpoints tonight and mostly clear skies. Most
guidance develops fog in the mountain valleys and the more common
spots in the Piedmont. Across the Piedmont however, conditions aloft
remain too dry to expect dense fog or critical vsby reduction. The
trend toward higher humidity continues tomorrow as thicknesses
increase with the building upper ridge and low level WAA continues
around the surface high.


At 140 PM Sunday: Not much change needed to the going fcst. The
models continue to agree well wrt the high confidence ridging
pattern, which has progged little in the past 24 hrs. A strong ulvl
sub-trop ridge will continue to build east through the
period....while Atl sfc ridging remains in place. Model soundings
show a pronounced subs inversion developing with h8 temps
increasing to 12C-14C each afternoon. This will limit any sfc-based
convection to the development of fair wx Cu which will be more
likely across the srn zone in a relatively higher sw/ly moist layer.
There could be some brief and highly isol -shra/tstms across the
higher terrain late Wed afternoon...but besides that the main wx of
interest will be the above normal temps with maxes reaching around
10 degrees above normal each day. Mins will remain right around
normal in good cooling conds with no frost/freeze concerns across
the higher elevations.


At 230 PM Sunday...the medium range continues to give the models
some fits with how to handle the flow regime over the east and
southeast late in the week. The model guidance has started to show a
bit better run-to-run continuity. It now appears to be a question of
whether the main upper flow will feature a full latitude progressive
trof, or if a low will cut off in the srn stream. Think the
progressive full latitude trof has a better chance of working out
across our region and that scenario, similar to what is depicted by
the ECMWF, will be favored in the new fcst. This scenario also
follows the old rule about forecasting dry weather when in a
drought. If the new ECMWF is correct, a lot of people will be
disappointed because we will get just a quick shot of showers with
the cold front that would barely put a dent in rainfall deficits.
The low pressure system over the wrn Atlantic is a complicating
factor because it would tend to prevent much Gulf moisture from
moving nwd ahead of the cold front approaching from the west. The
model trend suggests cutting back on the time range that precip
chances are forecast, thus we dry out Friday night and thru the
weekend. It also suggests limiting precip probability to the chance
range. Temps should also cool down a bit faster with frontal passage
happening earlier and quicker, so min temps Friday night were
knocked down 5-10 degrees, but probably still too warm for much
frost potential over the NC mtns.


At KCLT and elsewhere: Winds will generally favor the SW, with only
modest daytime gusts. Sky cover is expected to be minimal, except in
Mountain valleys where daybreak LIFR fog and cigs are possible.
Daybreak vsby restrictions are possible at some foothills sites this
morning, but at this time KCLT/KGSP/KGMU are not completely favored
by a model blend.

Outlook: Surface high pressure, drier profiles, and ridging aloft
will set up across the region through the middle of the week. The
potential for mountain valley fog and low stratus will continue each

Confidence Table...

            05-11Z        11-17Z        17-23Z        23-00Z
KCLT       High 100%     High  83%     High 100%     Low   56%
KGSP       High 100%     High  83%     High 100%     Low   56%
KAVL       High 100%     Med   66%     High 100%     Low   56%
KHKY       High 100%     Med   66%     High 100%     Low   56%
KGMU       High 100%     High  83%     High 100%     Low   56%
KAND       High 100%     Med   66%     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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