Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 160616

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
216 AM EDT Fri Mar 16 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 155 AM: The primary concern for the immediate near term is the
very windy conditions along the higher ridges of the North Carolina
mountains. Nearly all models have about 50 kt of flow at 850 mb, but
temperature advection at that level is fairly neutral. This is
yielding some 50+ mph gusts at elevations from 4500 to 6000 feet,
with damaging gusts above that, but much less wind mixing down into
the high mountain valleys. In collaboration with RNK, we will be
addressing this with an SPS targeted for the higher elevations
through the early morning hours, with winds diminishing around

Otherwise, the upper ridge axis to the west of the area will
steadily flatten through tonight as closed low pressure lifts
northeast from the plains to the midwest. Closer to home, a backdoor
surface boundary will remain draped over western NC today, but with
little to no attendant forcing or better moisture. This will permit
good insolation with temperatures warming back into the 70s over the
southern tier, except mid 60s near the I-40 corridor closer to the
front. Dewpoints should moderate from the extremely dry values
yesterday as some rebounding occurs under southwesterly flow.

Meanwhile, the closed low pressure evolving over the plains will
generate convection over the lower MS River Valley today. This
activity may make a run eastward toward or through the southern
Appalachians during the early morning hours Saturday. The hi-res
models mostly have showers arriving after 06Z Saturday morning.
Surface-based instability should be quite limited tonight, but there
is potential for elevated instability in the upstream warm sector,
and 850 to 500 mb lapse rates will steepen a bit through the period
as well. Will thus introduce slight chances of thunder in southwest
sections for the pre-dawn hours, though nothing severe is expected.


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 conditions should continue through the
period as a backdoor front settles through western NC, but with very
limited forcing and moisture. The main concern early in the period
will be LLWS at KAVL and at KCLT as a 40 to 50 kt low level jet in
the westerly flow rides in atop lighter lower elevation winds before
daybreak. Otherwise, expect some flavor of SW to WNW flow through
the day, with winds dimnishing steadily as the gradient weakens.
KAVL will be the main exception, with continued gusty NW winds.

A band of showers arriving along a diminishing convective cold pool
may impact the area from the west overnight. Any showers surviving
into the region should arrive mainly after 06Z, but PROB30 for SHRA
is warranted late in the period at KAVL and then overnight at KCLT
with the 30-hour TAF. Thunder currently appears unlikely overnight.

Outlook: Chances for scattered precipitation and restrictions
continue over the weekend. Chance look much better for next Monday
and Tuesday, with a stronger low pressure system arriving from the

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
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:




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