FXUS62 KGSP 181137

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
637 AM EST Mon Jan 18 2021

Dry high pressure will gradually build into the area today through
Tuesday. A weak cold front will lay down across the region late
Tuesday, stalling out across the Deep South for Wednesday through
Friday. Cool high pressure then builds in from the north for
the weekend.


As of 624 am EST: Showers continue to be forced by the passage
of a short wave across the region at this hour, aided by an
injection of stratospheric vorticity associated with a tropopause
fold passing to the north early this morning. The low level flow,
being westerly, is not as favorable as it could be, but was also
contributing to the forcing at low levels. Fewer showers are noted
upstream, which indicates that we are transitioning to more of a
traditionally-forced upslope precip situation. The high elevation
Winter Weather Advisory will be kept in place. We are running out
of time for any of the showers to break containment and move east
of the Blue Ridge as the upper trof axis was passing overhead at
daybreak, but any snow accumulation would be insignificant. The
passage of the upper trof axis should carry this potential to our
east by mid-morning.

All indications are that deeper moisture will pull out from the
mtns by midday, with the low level moisture drying up by the late
afternoon, as the low level flow gradually backs to WSW. This
should bring an end to the production of snow showers along the
TN border by the time our Advisory runs out. Meanwhile, east of
the Blue Ridge, it looks like a classic winter day with bright
sunshine, a WSW breeze, and temps climbing just shy of normal, all
courtesy of sfc high pressure passing to the south. The upper flow
pattern comes around to nearly zonal tonight as we come under the
rapid confluence of the split flow to the west. High pressure will
more or less remain in control as it ridges up from the south. Low
temps will also be a bit on the cool side of normal.


As of 230 AM Monday: A shortwave trough will swing thru the Great
Lakes Tuesday into Tuesday night, bringing a weak cold front into
the area. The front will sort of lay over the area form the north,
with low-level flow staying westerly ahead of the passage. The front
will bring a round of some low-level moisture, enough for at least
slgt chc to low-end chc PoPs across the westerly upslope areas of
the NC mountains. Any snow accums should be very light. Otherwise,
an uptick in cloud cover and breezy west winds is expected as
front passes. Weak high pressure builds in across the Deep South
on Wednesday under zonal flow aloft. Temps will be at or slightly
above normal Tuesday thru Wednesday.


As of 245 AM Monday: A highly zonal upper pattern will persist
thru the end of the work week, then some ridging across the
eastern CONUS is expected this weekend. Models still struggling
with embedded shortwaves riding thru the fast flow aloft. They
seem to agree that an area of low pressure will try to organize
over the Southern Plains, activating a frontal zone across the
Southeast. But as to how much moisture spreads atop the forecast
area is still in question. The 00z GFS and ECMWF have trended a
little wetter, spreading some QPF across nearly the entire forecast
area Thursday morning. If the precip starts late Wednesday night,
there may be a wintry mix in the mountains, but with little to no
accums, as thicknesses rise Thursday. Did bump PoPs up a little
bit to reflect the trends, but confidence is still on the low side
Wed night thru Friday. From there, should see another area of high
pressure nose down from the north, bringing temps back down to
near or slightly below normal, after being slightly above normal
Thursday and Friday. With the upper pattern beginning to amplify,
the medium range guidance shows a low pressure system developing
over the Plains. But confidence is low on any of that moisture
reaching our area before Day 7 (Sunday).


At KCLT and elsewhere: VFR should prevail at all TAF sites
through the period. Cannot rule out a passing snow shower at KAVL,
but earlier activity was more robust on radar and did not pose
any restrictions. High based stratocu will be the rule through
the morning hours near the westerly upslope areas of the mtns,
but the moisture is expected to dry up during midday. Guidance
suggests a westerly cross-wind at KCLT today, but think it more
likely the direction will prevail from the WSW. Expect occasional
gusts through mid-afternoon with deep mixing at all TAF sites. Wind
should diminish late in the day, and may come around to WNW for
a period of time this evening. Some high clouds will move in late
tonight or early Tuesday morning.

Outlook: VFR conditions are expected Tuesday through
Wednesday. Moisture and restrictions could return later in the week,
possibly Thursday.

Confidence Table...

            11-17Z        17-23Z        23-05Z        05-06Z
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 are available at
the following link:



NC...Winter Weather Advisory above 3500 feet until noon EST today
     for NCZ033-048>052-058-059-062.



NWS GSP Office Area Forecast Discussion