Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 220742

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
342 AM EDT Thu Mar 22 2018

Dry and unseasonably cool high pressure will dominate our weather
through Friday. The next low pressure system will cross the region
from the northwest over the weekend, with cooler and drier Canadian
high pressure building down over the area early next week.


As of 330 AM EDT: A Wind Advisory and Special Weather Statement
remain in effect for portions of the NC mountains through this

A few lingering snow showers may continue over the next few hours
along the TN border as well as a few snow flurries eastward along
the Blue Ridge, though returns are nearly non-existent at this time
as the moisture supply continues to be cut off as seen from latest
satellite imagery. A Special Weather Statement is in effect through
this morning as isolated patches of black ice are possible in the
areas previously under the winter weather warning/advisory.

Otherwise, conditions are quiet this morning with temperatures in
the low to mid 30s across the NW Piedmont and Upstate, back into the
20s across the NC mountains. After a week filled with unsettled
weather from thunderstorms and subsevere hail to a few snow events
across the NC mountains where up to 10 inches of snowfall was
reported in Jackson county (NC) last night, today and tonight will
be the first quiet weather forecast period of the work week. With
the fourth nor`easter this month well on it`s way up the eastern
seaboard and high pressure building in from the west, a tightened
pressure gradient across the NC mountains continues to produce gusty
NW winds this morning, thus warranting the issuance of the Wind
Advisory earlier this morning following the cancellation of the
Winter Storm Warning and Winter Weather Advisory. Gap winds have
developed as well, and may bring gusty winds down through AVL into
GSP through the morning hours. Per latest guidance, expect the
pressure gradient will relax later this morning (early afternoon at
the latest).

With clearing skies on tap for today, so are warmer temperatures
compared to what we saw yesterday, with upper 50s across the
Upstate, mid 60s across the NW Piedmont, and cooler into the overall
40s across the mountains. These above freezing temperatures will
allow for snow to melt this afternoon, but with temperatures
expected to dip back into the 20s tonight, any water/residual snow
that did not evaporate with the gusty winds will refreeze. On area
roadways and elevated surfaces such as bridges and overpasses,
expect black ice to potentially become a widespread concern tonight
through into early Friday morning and motorists should use caution.
If the road/ground surfaces look wet, assume it is black ice. Across
the northern foothills and northern portions of the NC piedmont,
overnight temperatures will dip to near or just below freezing,
remaining a few degrees warmer across the Upstate.


As of 325 AM Thursday: A 500 mb closed low system over NY/PA on
Friday will move east off Cape Cod by early Saturday. Deep layer
northwest flow behind this system will persist through Friday
night, with mainly mid clouds moving southeast over the area to
keep temperatures on the cool side of climo.

The ridge over the southeast will flatten over the weekend as a
prominent wave drops from the upper Midwest to the central
Appalachians. Deeper moisture and better forcing will arrive from
the northwest on Saturday as isentropic upglide develops quickly
over the activating warm front. Mixed precipitation looks quite
possible along and north of I-40 in western NC Saturday
morning and will keep the forecast ptypes rain versus snow
for now. Saturday afternoon temperatures will be a good 10 to 20
degrees below climo across the norhtern tier and 5 to 10 below
climo in the south.


As of 335 AM Thursday: There is good model agreement on a
vigorous surface low moving from Missouri down the frontal zone
to the southern Appalachians Saturday. There is also good
consensus on the low system transitioning quickly to the coast
on Sunday, with cooler air spilling southward from dominant
Ontario/New England high pressure in damming fashion. Meanwhile,
mid and upper drying will quickly wrap from the west on Sunday,
but low levels could remain a bit moist as cooling occurs from
the north in the developing cold air damming. The ptype forecast
for any slight chance to chance PoPs will follow partial
thicknesses methods.

The deamplifying wave will move off the coast on Sunday, with strong
ridging developing over the east Monday through Wednesday. The
primary difference between the GFS and ECMWF is that the GFS allows
the lower level moisture to linger through the period. The
preference is that the strength of the southeast ridge should
greatly restrict precipitation chances Mon through Wed, so will lean
toward the drier ECWMWF solution in this regard. Ptypes will
continue to follow partial thickneses for any slight chance weather.
Temperatures will transitions from minus 15 below climo on Mon
to a category above climo by Wed.


At CLT and elsewhere: Expect VFR to prevail through the valid TAF
period. FEW/SCT mid to high level clouds continue to linger across
the area this morning, with a drying trend expected to continue
today and through early Friday morning as sfc high pressure builds
in. This feature along with the exiting system to the northeast will
allow for a tightened pressure gradient to persist across the NC
mountains. Thus, have kept gusts at KAVL through today, with gusts
at KGSP/KGMU through this morning as well given the development of
gap winds. Gusty winds (with the exception of KAVL) will subside
through the late morning hours, with low end gusts returning into
the afternoon hours, persisting into the evening hours.

Outlook: Increasing precipitation chances and possible flight
restrictions are possible this weekend with another approaching
storm system. Otherwise expect VFR.

Confidence Table...

            07-13Z        13-19Z        19-01Z        01-06Z
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:


NC...Wind Advisory until 11 AM EDT this morning for NCZ033-048>050-


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