Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201033

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
633 AM EDT Thu Oct 20 2016

Warm temperatures will continue today as a cold front approaches
from the Mississippi River Valley. The front will cross the area
tonight through Friday morning with increasing rain chances -
especially over the mountains. Drier and much cooler conditions will
set up across the area over the weekend. A dry front will push
through from the north on Monday with cool high pressure remaining
in place through Wednesday.


1030 UTC Update: Winds were updated with a blend of the latest NAM
and ADJMAV guidance. Areas of daybreak fog were updated based on

At 200 AM Thursday: An upper ridge will weaken and drift of the
Carolina and GA Coasts today as an upper trough progress to the MS
River Valley. This trough reaches the OH and TN River Valleys

A surface cold front will cross the OH and Mid MS River Valleys
today. The front and its associated moisture are expected to reach
the Southern Appalachians late this afternoon, crossing the
Foothills and Piedmont overnight. While convection is briefly
possible in the NC Mountains this afternoon, instability wanes this
evening. A lack of isentropic upglide and upslope flow will limit
precipitation production over our area, especially east of the Blue
Ridge. Temperatures will run well above normal today and tonight,
with, with records highs in jeopardy in some locations today.


As of 240 AM EDT Thursday: An amplified 500 mb trough and associated
surface cold front will cross the forecast area Friday morning.
Although the deeper moisture along the frontal zone is fairly
narrow, there should be enough upper forcing from DPVA and jet
divergence to warrant likely PoPs in northern and western sections
and fairly solid chances in the heart of the forecast area. However,
QPF will be limited by the rapid pace of the front and all of the
deeper moisture with the cold front will be east of the forecast
area by 18Z Friday as dry air wraps in quickly from the southwest.
Although thunderstorms cannot be ruled out just ahead of the front,
pre-frontal flow should not be very backed and the best shear will
be just behind the boundary. Surface instability also looks quite
limited given the morning timing of the fropa.

The main story post-fropa will be windy conditions in the mountains
along with much colder air spilling into the region. Expect about 40
kt of 850 mb flow during the peak of the cold advection Friday
afternoon to Saturday morning. Northern NC mountain wind gusts will
likely remain just below advisory, but an HWO mention for possibly
very windy conditions will likely be added. Still expect 850 mb
temps to bottom out slightly sub-freezing early Saturday morning,
but low level moisture does not look very impressive. Will still
feature a ridge top rain/snow mix Friday night and cannot rule out
some light accumulations on Mount Mitchell by Saturday morning where
temperatures should fall into the upper 20s. A widespread Saturday
morning freeze does not look likely in the NC mountains and winds
will be too high for frost formation so no frost/freeze products
will be issued. Elevations above 4000 feet, however, could well see
plenty of lower 30s temperatures.

Additional H5 vorticity will traverse the northern half of the
forecast area on Saturday in deep layer NW flow aloft, but lingering
low level moisture will dry up quickly. Temperatures will fall well
below climo by Saturday with plenty of 40s/50s maxes in the
mountains and 60s east.


As of 245 AM EDT Thursday: Fairly innocuous WNW flow will continue
through the late weekend, with surface ridging settling over the
southeast. There may be some frost potential in the SW mountain
valleys Sunday morning as the pressure gradient and NW surface winds
steadily diminish. Temperatures will rebound to at or above climo
through Sunday afternoon with a light downslope flow continuing east
of the mountains.

A weak clipper system will pass by to the north Sunday night into
Monday and drive a backdoor surface cold front into the region. The
backdoor boundary will settle south of the area on Tuesday with a
strong surface high ridging down from the north through mid week.
Aloft...upper ridging will build in from the west through mid week
to keep conditions dry.


At KCLT and Elsewhere: Best bets for fog are this morning in the NC
Mountain Valleys SW of KAVL, and at KCLT, based on the latest
observations. KCLT dew point depression is marginal, and fog has
been noted at surrounding areas. Cig restrictions remain limited to
the Mountain Valleys SW of KAVL as in previous mornings. Outside the
valleys of SW NC, cloud heights should favor low VFR, but without
enough coverage for a cig until this afternoon at KAVL, this evening
at foothills sites, and overnight at KCLT. Winds will favor the S
today and this evening as a front approaches from the west, veering
NW at KCLT and foothill sites overnight. Rainfall chances ramp up
this evening at KAVL, with thunder possible early in the evening.
Rainfall chances spread east across the foothills and piedmont
overnight, but thunder chances diminish. Winds should remain up
overnight, and with rainfall amounts limited, chances of vsby
restrictions are modest.

Outlook: A front will move through the area on Friday, bringing
light rain, a period of gusty winds, and perhaps restrictions due to
cloud cover. Cool/dry high pressure returns for the weekend keeping
chances for restrictions low.

Confidence Table...

            10-16Z        16-22Z        22-04Z        04-06Z
KCLT       High  91%     High 100%     High 100%     High 100%
KGSP       Med   75%     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       Med   66%     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:



  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      83 1985     42 1961     62 1950     25 1981
   KCLT      86 1926     49 1989     66 1993     30 1972
   KGSP      86 1899     50 1989     68 1894     29 1972




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