Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 250817

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
317 AM EST Sat Nov 25 2017

A fast-moving and relatively dry cold front will cross the area later
today. In the front`s wake, another round of dry high pressure will
overspread the region and persist into the middle of next week.


As of 230 am EST: Water vapor satellite imagery shows a broad,
amplifying trough digging into the Ohio Valley early this morning.
Mid and high level moisture ahead of the system will increase in
earnest across the region through the day. Despite the increased
cloud cover, warming thicknesses and improving southwesterly flow
ahead of a surface lee trough near the mountains will permit maximum
temperatures to rebound to above climo values this afternoon.
Meanwhile, lead vorticity lobes with the upper trough will cross the
region late this morning, with better vorticity along with improved
upper level divergence arriving this afternoon just ahead of an
associated surface cold front. Vertical profiles limit any deeper
moisture in the sub 850 mb layer to the higher terrain. Will thus
confine any slight chances of showers to the immediate Tennessee
border this afternoon.

Anticipate deep layer drying in the northwest flow tonight, however,
low-level moisture may linger along the spine of the NC mountains
overnight. In addition, breezy conditions will likely develop over
the high terrain, but with gusts remaining sub-advisory during the
peak of the cold advection overnight. The passing surface cold front
will settle southeast of the region overnight. Nighttime mixing will
likely keep minimum temperatures just above climo despite the
frontal passage.


As of 250 AM EST Saturday: the short term fcst picks up at 12z on
Sunday with broad upper trofing centered over New England, and steep
upper ridging over the Western CONUS. By early Monday, heights will
begin to recover as the trof axis lifts northeast and ridging spreads
farther east. By early Tues, the ridge will flatten as it moves over
the fcst area. At the sfc, another round of dry high pressure will
overspread the region on Sunday and linger into the extended period.
As for the sensible fcst, the period should be dry. High temps will
cool back down to near climatology on Sunday and Monday, with lows
about a category below normal for late November.


As of 235 AM EST Saturday: the extended fcst picks up at 12z on Tuesday
with flat upper ridging over the southeast and another northern stream
upper trof rapidly approaching the Great Lakes. At the same time, a
southern stream H5 low will close off over the SW CONUS and Southern
Rockies. This low will gradually lift northward and open back up as a
shortwave as it moves eastward. The long-range models now have the
feature approaching the fcst area by early Thurs, with the 12z ECMWF
being quite a bit faster and farther to the north than the GFS and CMC.
Regardless, as the shortwave moves offshore on Thurs, another fast-moving
upper trof will dig down across the Great Lakes and move over our area
by early Fri. This trof is expected to move well east of the region
by early Sat with heights recovering in its wake. At the sfc, broad
high pressure will be in place over the region to start the period.
The center of the high is expected to drift off the Atlantic Coast by
late Tues/early Wed, as a fast-moving cold front moves across New
England but remains well to our north. On Wed and Thurs, the models
try to develop a weak low over the Southern Plains and then lift it
northeast towards the Great Lakes and Ohio River Valley. As this occurs,
the low deepens and a cold front intensifies and approaches the fcst
area late Thurs. The front moves quickly thru the CWFA early Fri and
is expected to be moving offshore by Fri afternoon. In its wake, strong
and dry high pressure spreads back over the region.


At KCLT and Elsewhere: Cirrus will continue to increase and thicken
from the west today as a trough digs through the Ohio River Valley.
Some patchy fog may develop given the small depressions and light to
calm winds, but will keep conditions VFR at the TAF sites through
daybreak. Winds will pick up from the southwest with mixing this
morning as a lee trough sets up just east of the mountains and a
cold front approaches from the northwest. Expect mainly altocumulus
or cirrus ceilings for much of the day before the upper support
moves east by evening, with deeper layer northwest flow drying
tonight. Will keep the TAF sites dry with any better shower chances
confined to the TN border area. Post-fropa northwest winds may
become gusty tonight at KAVL as cold advection develops. At the
foothill and piedmont sites, expect winds to slowly veer from
southwest to west with the approaching/passing front.

Outlook: Expect VFR conditions to continue Sunday through Thursday
as dry high pressure sets up across the region.

Confidence Table...

            08-14Z        14-20Z        20-02Z        02-06Z
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 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High 100%

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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