Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 180146

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
946 PM EDT Mon Oct 17 2016

Dry high pressure will dominate the region for most of the week with
temperatures rising to well above average. Moisture and rain chances
will return by the end of the work week as a cold front crosses the
region from the west. Dry and much cooler conditions will likely set
up across the area over the weekend.


As of 945 PM Monday: Quiescent conditions require little change
except to touch up temp trends based on latest obs. Deep layer
ridging to prevail across northeast GA and the western Carolinas
through the near term fcst period. Upper heights will continue
to rise across the southern Appalachians over the next 24 hours
as a sprawling H5 anticyclone migrates eastward to reinforce an
east coast surface ridge. With that, the fcst will remain dry
as deep subsidence is evident on various fcst soundings, even
over the mtns. Skies should remain mostly clear, though a few
clouds may advect into the Piedmont later tonight, being trapped
beneath the inversion. Given abundant radiational cooling along
with substantial llv moisture, mtn valley fog should form in the
predawn hours and last through mid morning, being dense in spots
around daybreak. Portions of the Piedmont will see only light/patchy
fog. Temperatures through the fcst period will remain nearly 10-12
degrees above normal.


As of 205 PM EDT Monday: Upper ridging over the area Wednesday
begins to break down Thursday as a deep upper trough develops over
the MS River Valley. A similar pattern is seen at the surface with
high pressure Wednesday breaking down Thursday as a cold front moves
into the OH and Lower MS River Valleys. Expect dry conditions
Wednesday with a strong cap in place, although there will be an
increase in afternoon cumulus across the mountains. There may be
enough moisture and instability moving in ahead of the front
Thursday for some late day isolated convection across the mountains.
Otherwise, dry conditions expected elsewhere. With very high
thickness values remaining in place both days, highs will be up to
15 degrees above normal Wednesday then falling a couple of degrees
Thursday with increased clouds. Lows will be nearly steady up to 15
degrees above normal.


As of 215 PM EDT Monday...the recent trend continues in the ECMWF
whereby the upper trof late in the week remains progressive...
although the 00Z run does not have the amplitude as high as previous
runs. A quick look at the 12Z run keeps this trend going.
Meanwhile...the 12Z operational GFS run has come more in line with
the progressive scenario. Both models, with the progressive trof,
keep the low over the western Atlantic well to our east. So,
confidence has increased a bit more that we should have a quicker
and cleaner frontal passage during the Thursday night/Friday time
period, and the fcst reflects more of that refinement of timing in
the precip probability. The mtns have the best chance of precip late
Thursday night as the front comes in from the west...up into the
Likely range on the TN border...but precip chances fall off from
there. The precip chance still appears more tenuous east of the Blue
Ridge for Friday. Not ready to abandon precip chances altogether as
suggested by the ECMWF, so in that regard the GFS is favored east of
the mtns on that day. However, it now appears that precip should be
all but over around sunset Friday away from the TN border. One
interesting wrinkle in the guidance is the possibility of some NW
flow precip early Saturday morning while the GFS steady drops 850mb
temps down below zero C under cold advection. It is probably a week
or two early for NW flow snow, but I would not be surprised to learn
of a few snowflakes above 6k feet in the pre-dawn hours Saturday IF
the GFS is correct. The rest of the fcst should be quiet under a
broad NW flow aloft and high pressure building in from the west thru
the weekend, followed by high pressure moving overhead early next
week. The only problem might be min temps Saturday night and Sunday
night over the mountains, but at this point valley locations will
probably only make it as low as around 40 degrees F...not quite low
enough to worry about a frost/freeze just yet. Ridgetops might get
close to freezing though. Expect temps below normal for Saturday,
moderating to near normal by Monday.


At KCLT: VFR. Offshore high pressure will sustain a light SW flow
thru the area. A robust inversion will be present aloft, but it
presently appears there will not be enough moisture beneath it to
expect any low clouds until mixing gets underway late morning.

Elsewhere: As for KCLT the prevailing lo-lev flow will be SW
and skies will remain clear overnight, except over the mountains
where the remainder of the afternoon`s cumulus will be trapped
beneath the inversion, slowly dissipating. Patchy fog should
develop again in/around KHKY, and valley fog is likely to settle
over KAVL at daybreak. Moisture profiles are progged to be less
supportive of fog at KAVL so the mention is kept in TEMPO. At KHKY
a TEMPO reflects the expectation that vsby will change rapidly,
restricting only for brief periods.

Outlook: Warm and mostly clear high pressure will remain over the
region through the middle of the week. The potential for mountain
valley fog and low stratus will return each morning. A front will
move through late in the week, bringing back cool autumn air,
and perhaps restrictions due to cloud cover.

Confidence Table...

            01-07Z        07-13Z        13-19Z        19-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     Med   67%     High 100%     High 100%
KHKY       High 100%     High  80%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High  93%     High  96%     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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