Area Forecast Discussion
Issued by NWS Greer, SC

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816
FXUS62 KGSP 242358
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
658 PM EST Tue Jan 24 2017

.SYNOPSIS...
Mild high pressure will build over our region from the south
through Wednesday. A cold front will move through the forecast
area early Thursday...bringing colder temperatures to the
region for Friday and the weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
2315 UTC Update: Sky cover was updated from visible satellite
imagery, with only minor changes resulting.

As of 220 PM EST: A prominent upper ridge axis stretches from the
mouth of the Mississippi River to the Great Lakes this afternoon. At
the surface, lee troughing from northwesterly downsloping flow has
set up just southeast of I-85. Profiles are quite dry up the column
throughout the region and the only lingering clouds are scattered
stratocumulus in the lingering northwesterly upslope flow near the
Tennessee border. These clouds should dissipate quickly through
early evening. Anticipate the pressure gradient slackening with time
late today and winds becoming light tonight. Will shade temperatures
toward the cool side of guidance overnight with improving radiating
conditions.

The upper ridge will be firmly atop the area around daybreak
Wednesday. Southwest flow return moisture in the pre-frontal
humidity band approaching from the west will arrive in the western
mountains by late afternoon. Any slight chance PoPs for showers
through late day will be confined to mountain locations southwest of
the Smokies. Will nudge temperatures toward the warmer end of the
guidance envelope Wednesday afternoon given recent model performance.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 220 PM EST Tuesday: An upper ridge will slide off the East
Coast Wednesday night with broad upper trough being carved across
nearly the entire CONUS Thursday thru Friday. At the surface, a low
pressure system will lift NE from the Central Plains to the Great
Lakes, dragging a cold front across the Ohio Valley to the
Appalachians overnight Wednesday night. The front will pick up a
little moisture and should bring a narrow band of showers into the
NC mountains by around midnight. The shower activity will likely
struggle to survive east to the I-77 corridor, so PoPs will feature
likely along the western edge of the CWFA to chance east. The precip
should fall as all rain, with well above normal temps across the
region, and should exit east of the area by late morning Thursday.
QPF amounts will be light.

As the low crosses the Great Lakes, wrap-around moisture should keep
a stratocu deck along the TN/NC border, with low-level flow becoming
NWLY. CAA will ramp up, but downslope warming will cancel out much
of that to allow temps to warm into the mid to upper 50s east of the
mountains. Meanwhile, temps will generally fall in the high terrain.
The GFS is pretty much the only operational model with NW flow
precip Thursday, but given the moisture seen in the NAM and EC, I
think keeping a slight chc for RA/SN showers looks good. Any accums
will be very light.

Thursday night and Friday, flow becomes briefly zonal aloft, but
then more energy dives into the broad upper trough, continuing the
height falls across the region. The models agree on another slug of
850 mb RH with slightly veering of the flow, which should result in
an uptick in snow shower chances along the TN/NC border. PoPs still
remain in the slight chc to low-end chc range, however, with only
very light snow accums expected, mainly in the Northern Mountains.
Temps will be noticeably cooler, with lows near normal and highs
slightly below normal.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 225 PM Tuesday...the medium range still looks like a whole
different season compared to what we`ve had lately, with temps back
down at or below normal and much more typical of winter in the
western Carolinas/northeast GA, at least through Monday night. The
main driver will be an upper trof that persists through the weekend
that allows easy access to the colder air. This pattern may bring
more than one short wave and surge of low level moisture from the
W/NW across the NC mountains. Expect this to yield periods of NW
flow snow, the first of which may already be underway Friday evening
on the TN border. Moisture is deep enough to suggest the potential
for enough snow to measure, but for now we keep the fcst
conservative with precip prob limited to the chc range and precip
amts on the low side. The moisture pulls out Saturday morning, so
expect a lull. Another surge at low levels might bring more flurries
to the TN border Saturday night, followed by another lull Sunday
morning. The most interesting time is still the late Sunday/early
Monday time frame as the GFS shows a strong short wave diving down
and sharpening the upper trof axis, right over the Srn Appalachians
at 12Z Monday. Expect more snow shower activity to develop over the
mtns, mostly near the TN border, as this feature passes. The
strength of the vort center diving south of the fcst area early
Monday would suggest a chance that some of the snow shower activity
would break containment and move out across the western
Piedmont/Upstate/northeast GA on Monday morning. Several members of
the GEFS support this idea, but the ensemble shows the operational
GFS to be the most enthusiastic about this prospect. Meanwhile, the
new ECMWF is dry, with the wave passing several hundred miles
farther north, but this model shows poorer run-to-run continuity. At
this point, think it best to not get excited about the potential for
snow outside the mtns, as it would probably amount to less than an
inch anyway. We`ll keep it in the back of the mind going forward,
though. Monday will be the coolest day as the thermal trof bottoms
out. NW flow snow continues into the evening, but should end early
Tuesday as the moisture pulls out. Tuesday looks like the day our
temps moderate as an upper/sfc ridge builds in from the west.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and Elsewhere: Winds will diminish slightly overnight,
backing from west to southwest east of the Blue Ridge, but remaining
NW at KAVL. Wind speeds increase on Wednesday ahead of an
approaching cold front, remaining from the SW east of the Blue
Ridge, amd backing to the SW at KAVL. Overnight vsby restrictions
are not expected in a dry airmass with winds remaining up slightly,
and cig restrictions are not expected, although high cigs may reach
KAVL late Wednesday.

Outlook: Brief return flow moisture is possible ahead of the next
cold front Wednesday night into Thursday, with colder air and NW
flow moisture setting up through the weekend.

Confidence Table...

            00-06Z        06-12Z        12-18Z        18-00Z
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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...JPT
NEAR TERM...HG/JAT
SHORT TERM...ARK
LONG TERM...PM
AVIATION...JAT



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