Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 152030

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
430 PM EDT Thu Mar 15 2018

Dry high pressure will remain over the region into Friday.  A cold
front will bring showers and cooler temperatures to the region to
begin the weekend...then dry high pressure builds back in from the
north Sunday. Another moist front will approach the area Monday and
cross north into Tuesday.


As of 430 PM EDT Thursday: Fcst still looking ok for the remainder
of the afternoon and into the evening, with Spring-like temps and
gusty WSW winds. No changes other than for current conditions.

The next 24 hours are expected to be relatively quiet with a welcome
return to more normal or above normal temperatures, but there
are a couple of minor complications, at least over the northern
zones. The upper pattern will be slowly progressive, with the upper
trof moving slowly off the east coast and an upper ridge creeping
eastward toward the fcst area on Friday. The NW flow aloft will
continue thru the period, altho the gradient will relax enough such
that wind should not be significant on Friday. As for complications,
the first one comes tonight as a sfc boundary drifts down from the
N. The guidance has some pooling of low level moisture to the S of
the boundary, which is run up the W slope of the nrn mountains of
NC by the weakening NW flow aloft. The guidance actually spits out
some light precip after midnight and through mid-morning Friday,
but there seems to be little interest for including anything more
than a brief small chance after daybreak over Avery County. At any
rate, the precip should not be significant and temps should remain
above freezing. High pressure moving past to the south should
allow some moisture return ahead of the system approaching from
the west on Friday, which should keep the RH from bottoming out so
low in the afternoon. See little in the way of forcing for precip
reaching the fcst area before the end of daylight, so the fcst
was kept dry. The other complication will be the location of the
weak front that drifts in from the north in the afternoon, which
the guidance suggests might make it down to the NW Piedmont late
in the day. If the front makes it this far S, the high temp fcst
for the NW Piedmont zones would be in some jeopardy. As it is, the
high temp in that location was kept similar to today, whereas the
rest of the fcst area is expected to get about five degrees warmer.


As of 230 PM Thursday...A mid level short wave and associated
surface low will move out of the Central Plains on Friday night and
across the Ohio Valley and Mid-Atlantic region on Saturday. An area
of showers will traverse the area late Friday night and Saturday
morning. A warmer and more moist air mass will move north into the
area on Saturday allowing some surface based instability to develop
in the afternoon. However, the more substantial forcing will have
exited the area by then. Thus, will carry a low chance of
thunderstorms in the afternoon Saturday. Some light rain shower
activity will continue Saturday night with this feature mainly in
the mountains.

High pressure will build south into the area on Sunday leading to a
dry and mainly sunny day.


As of 230 PM EDT Thursday...The latest guidance is in reasonable
agreement for the medium range. The upper levels will feature an
active quasi-zonal flow, with a compact, fast-moving closed low will
streak across the Central Plains Sunday night thru Monday. Then the
low will open up and become absorbed into a deepening longwave
trough as it enters the Ohio Valley Monday night thru Tuesday.
Overall height falls across the southern tier CONUS will result in a
strong low pressure system with center tracking along with the upper
low. The system will bring plenty of Gulf moisture and broad
isentropic lift atop the region starting Sunday night, maximizing
Monday night. Guidance agrees on in-situ cold air damming setting
up, with temps staying in the 40s and 50s across the CWFA thru the
day on Monday. With the wedge front draped across the I-20 corridor,
the operational models all have a maximum of QPF along/south of this
on Monday, with over 1000 J/kg of CAPE in the warm sector. This may
interrupt moisture transport into our area, and keep QPF amounts

The low will look sorta like a Miller-B cyclone heading into
Tuesday, with a secondary low developing near the VA capes, then
becoming the dominant low by early Wednesday (per the GFS), while
the ECMWF holds onto a low in the Great Lakes much longer. Either
way, the upper level trough looks fairly deep along the East Coast,
and another nor`easter should impact New England and Mid-Atlantic. A
persistent NW flow regime will set up atop the CWFA, with periods of
snow showers likely along the TN border starting Tuesday night,
possibly lingering beyond next Thursday. Temps will briefly rebound
to near or slightly above normal Tuesday, then cool to below normal
under the upper trough for Wednesday and Thursday.


At KCLT and elsewhere: VFR through the period with mainly just
some passing very high based stratocu this afternoon. Wind will be
the main issue, with frequent gusts from the WSW at all terminals
outside the mtns. KAVL will have gusty NW winds. The gusts should
diminish with sunset, but wind will remain relatively strong into
the evening. Some moisture may return along a weak boundary that
sags down across the nrn mountains of NC late tonight, bringing
some increased cloud cover, but the fcst was kept dry and ceiling
kept VFR on the TN border for the most part. On Friday, wind
will eventually shift around to WNW by late morning or early
afternoon. Gusts are not expected.

Outlook: Chances for precipitation and restrictions increase Friday
night and continue through the weekend.

Confidence Table...

            20-02Z        02-08Z        08-14Z        14-18Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     High 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:


Wind gusts in excess 30 mph and relative humidity as low as 20
percent were occurring across the area this afternoon. These
conditions will begin to improve by late afternoon as peak heating
wanes. A fire danger special weather statement that is handling the
situation well remains in effect until this evening.


NC...Wind Advisory until 8 PM EDT this evening for NCZ033-048>052.


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