Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 161052

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
652 AM EDT Mon Oct 16 2017

Light rainfall chances peak this morning as a fast-moving cold
front moves through the area.  Dry conditions and below-normal
temperatures will follow the front beginning this afternoon, and
persist through mid-week.  Warmer temperatures will return later
this week as deep-layer ridging sets up over the Southeast US.


As of 645 AM Mon: Wind shift line along leading edge of cold frontal
zone has pushed into the I-85 corridor at this hour. Bands of
showers associated with the front are moving quickly thru the CWFA,
and the bulk of these will be out of the area by 9-10 a.m. Abundant
moisture trails the front, with a fairly contiguous low stratus
deck west of the mtns; terrain effects are expected to limit
its expansion into our area. Dewpoints have not yet taken a hit,
which suggests the patches of stratocu that we are seeing will
linger until late morning, perhaps even expanding in some areas
under subsidence inversion. Accumulating precip is not expected
to redevelop in this scenario, however.

With cold advection taking hold early in the day, I used our
short-term consensus product to update hourly temp/dewpt trends
and based max values on that. Trends will be least diurnal in
the mtns but peak a bit earlier than usual in the Piedmont as
well. Tonight, winds will remain breezy as skies become virtually
clear. Bias-corrected MOS temps did well with the "cold snap"
we had at the beginning of the month, so those were preferred for
tonight`s mins. Conditions should be sufficiently moist for some
patchy frost to form in the mtn valleys and foothills, though wind
may promote enough mixing to keep it localized. Hence no advisory
will be raised at this time; day shift will take a second look.


As of 220 AM EDT Monday: Short wave ridging develops over the
Southeast Tuesday before a weak trof returns for Wednesday. At the
surface, cool and dry high pressure builds in Tuesday and remains in
place for Wednesday. Clear skies and light winds will lead to lows 5
to 10 degrees below normal both nights. This puts the mountain
valleys in jeopardy of frost development both nights and the
Northern Foothills and NW Piedmont in jeopardy Tuesday night. Highs
around 5 degrees below normal Tuesday rise to within a couple of
degrees of normal Wednesday.


As of 305 AM EDT Monday: An upper ridge axis builds over the area
through Saturday. At the surface, high pressure remains over the
area Thursday and Friday before sliding off shore on Saturday. This
results in dry weather with a warming trend. Highs start out
Thursday a couple of degrees above normal and rise to around 5
degrees above normal for Friday and Saturday. Lows start out a
little below normal and rise to a little above normal. The ridge
axis moves to the Atlantic coast or off shore on Sunday as deep trog
develops over the central CONUS. The guidance is in some
disagreement on how this trof develops. Both the GFS and ECMWF
develops a closed low at the base of the trof near the Gulf Coast.
However, the GFS is farther west as the northern stream wave splits
and moves east faster. The ECMWF keeps the streams more coherent and
is farther east with the closed low. This shows up at the surface as
the GFS holding the surface ridge in a little longer keeping our
area dry as the moist southerly flow is farther west. The ECMWF
breaks down the ridge allowing the moist southerly flow to move in
from the west faster. Given the differences, have kept Sunday dry
for now. Lows will be a little above normal with highs around 5
degrees above normal.


At KCLT and Elsewhere: Winds are expected to have shifted to NW or N
at all sites by 12z along leading edge of cold frontal zone. Under
a strong inversion, some moisture will remain trapped near the
sfc behind this wind shift, so some low VFR or even MVFR cigs
will continue to be seen thru late morning, and a few very light
showers may occur. Clearing will follow and little to no cloud cover
is expected in the remainder of the period. Some gustiness will
occur today as colder air filters in, particularly at KAVL. Frost
formation is a possibility at KAVL and other mtn valley locations
tonight, though light breezes will minimize coverage.

Outlook: Seasonably cool and overall VFR conditions will persist
through the work week.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
KCLT       Med   66%     High 100%     High 100%     High 100%
KGSP       Low   36%     High 100%     High 100%     High 100%
KAVL       High  94%     High 100%     High 100%     High 100%
KHKY       Med   66%     High 100%     High 100%     High 100%
KGMU       Low   36%     High 100%     High 100%     High 100%
KAND       Med   72%     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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