Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 201758

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
158 PM EDT Thu Oct 20 2016

After a stretch of record warmth, a cold front will cross the area
tonight through Friday morning, increasing rain chances mainly over
the mountains. Drier and much cooler conditions will set up across
the area over the weekend. A dry "back door" front will push through
from the north on Monday with cool high pressure remaining in place
through the middle of next week.


As of 155 PM: The current forecast remains on track. KGSP has
already tied the record high. I will update the forecast to decrease
early afternoon PoPs and sky cover.

As 1120 AM: Temperatures are once again on pace to reach record or
near record high temperatures. I will update morning temps to match
latest observations. Otherwise, the update will feature lower Pops
through the day and only high clouds through early this afternoon.

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 200 PM EDT Thursday...the extended period begins Sunday night
with the area under the influence of WNW flow and a weak surface
high centered over the southeast. Plentiful insolation and some
continued weak downslope flow east of the mountains will allow max
temps on Monday to climb to about ten degrees above average. A
clipper system will sweep through well to our north during the day
on Monday, pushing a backdoor cold front through by Monday night.
Though the frontal passage will feature no QPF response in our area,
it will bring min and max temperatures down closer to average levels
on Tuesday. An upper ridge will build in from the west by the middle
of next weak, keeping the region dry. Guidance is currently
suggesting a surface wedge will set up during the middle of the next
work week, maintaining temperatures near average levels.


At KCLT and elsewhere: Latest visible satellite indicated a shallow
CU field across the western Carolinas and NE GA. In fact, at 1715Z,
the CU was still absent over the rivers/lakes, still showing signs
of a thin layer of CIN. To the west, a sfc cold front was located
across the Ohio River Valley south across the western TN/KY. Thin
bands of showers and thunderstorms will likely develop along and
ahead of the cold front through this evening. By late tonight, low
pressure is forecast to deepen across PA, sweeping the front
across the southern Appalachians during the early morning hours,
reaching the central Carolinas by sunrise. South-southwest winds
should remain ahead of the front, then veering from the northwest
in the wake of the boundary. The environment should yield marginal
instability across the Appalachians, supporting showers and
thunderstorms. East of the mtns, it appears that showers will be
limited to the NC foothills and northern Piedmont. MVFR to IFR
clouds may remain across the TN border counties through Friday
morning. By mid Friday morning, shallow mixing should provide
enough momentum transfer to support gusts around 20 kts, gradually
strengthening through early afternoon.

Outlook: Pressure gradient will remain remain across the western
Carolinas through Saturday. Dry high pressure will build across the
region on Sunday into early next week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High  82%     Med   79%
KHKY       High 100%     High 100%     High  90%     High  97%
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:



  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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