Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 231804
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
104 PM EST Mon Jan 23 2017
A vigorous low pressure system will move east across the
Carolinas today then northeast up the East Coast through mid week.
Mild high pressure will move in Tuesday and Wednesday until a cold
front crosses the region Wednesday night.
.NEAR TERM /THROUGH TUESDAY/...
As of 1245 PM EST: Water vapor imagery shows the closed upper low
center moving east of the Charlotte metro area and surrounding
piedmont early this afternoon. This system will continue to slowly
pivot away to the east through late day, with the primary surface
low center reorganizing from east of the Blue Ridge to north of the
Outer Banks over the coastal waters. Deeper moisture and deformation
forcing have wrapped around the back side of the low, and scattered
to numerous showers will transit east across the foothills and
piedmont through the afternoon, with drizzle falling elsewhere,
before the forcing moves east through this evening. As the banded
forcing slides east, northwest flow upslope forcing and moisture
will increase across the western mountains this evening and
overnight. Thermal profiles continue to support mainly rain across
the mountains, however snow levels should continue to uncover
elevations above about 4000 to 5000 feet. This should allow the
higher ridges to see some light snow accumulations through the
overnight areas, but any advisory level accumulations would be
mainly at 5000 feet and up. In addition, the low level cold
advection jet during the peak of the northwest flow may reach around
50 kt along the Blue Ridge toward daybreak. The current Wind
Advisory still looks well placed, but some consideration of a Blue
Ridge vicinity High Wind Warning will be needed.
The 500 mb low center will move east off the Mid-Atlantic coast
overnight, with broad ridging building over the southern
Appalachians from the west through Tuesday. NW upslope moisture will
steadily dry up as well through the day on Tue with mountain winds
diminishing after Noon as the pressure gradient relaxes. Expect lee
troughing to develop east of the mountains through Tuesday
afternoon. Downsloping off the mountains should yield plenty of max
temps in the 60s over the foothills/piedmont.
.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 320 AM EST Monday: Upper ridge builds into the area Tuesday
then slides east Tuesday night. Lingering low level moisture and NW
flow Tuesday morning tapers off during the afternoon as high
pressure builds in from the west. Any lingering elevation dependent
rain or snow showers will dissipate through the morning as well. Do
not expect any significant additional accums. Very windy conditions
will continue through the morning across the mountains, so the wind
advisory will go through noon. Outside of the mountains, expect
clearing skies and breezy conditions. Winds will taper off during
the evening. Highs will be 5 to 15 degrees above normal with lows 10
to 15 above normal.
Heights fall Wednesday and Wednesday night as a trough moves out of
the central CONUS towards the area. Short wave energy moves into the
western portions of the CWFA by the end of the period. A cold front
moves into the area late on Wednesday then across the area Wednesday
night. There is some deep moisture and forcing associated with this
front. However, the band of moisture is narrow and the front is
quick moving. Bring some low end chance PoP into the western CWFA
late in the day and spread them east across the area during the
evening. Precip outside of the mountains should taper off after
midnight as the best moisture moves east and W to NW downslope flow
develops. With CAA developing behind the front Wednesday night,
elevation dependent rain or snow showers will develop. No
significant accums are expected for now. Highs will be around 15
degrees above normal with lows 10 to nearly 20 degrees above normal.
.LONG TERM /THURSDAY THROUGH SUNDAY/...
as of 145 AM Monday...for the period Thursday through Sunday. a
surface cold front will be crossing the Carolina coastal plain
Thursday morning with large high pressure over the Mountainous West
and low pressure over eastern Canada. The pressure gradient between
these 2 weather systems will set up a NW Flow of air from near or
just west of the Great Lakes to the southern Appalachians.
Atmospheric thickness values will be lowering late Thursday into the
weekend as the axis of the 500mb trough settles closer to the
Carolinas. NW Flow snow for the TN and NC mountains will occur
Thursday night through Friday and appears very possible again over
the weekend. In fact...there may even be a persistent NW Flow snow
for the NC mtns through the weekend. We have a few days to nail down
the forecast but certainly a strong signal for this event days in
advance. Both the GFS and ECMWF are in fairly good agreement
although the GFS is most supportive of the NW FLow event.
After having a long period of above normal temperatures, we can
expect near or just below normal temps Friday and Saturday. As the
trough axis gets near on Sunday we may be at least 2 or 3 degrees
.AVIATION /18Z MONDAY THROUGH SATURDAY/...
At KCLT: Lingering moisture under the slowly departing closed low
pressure system will produce mainly MVFR ceilings and occasional
light rain showers or drizzle through late afternoon. There is
fairly good consensus among the models/MOS on toggling winds more
WNW after 21Z and this has been followed. Expect the ceilings to
then gradually lift to VFR and scatter overnight. Winds could toggle
back toward WSW with lee troughing Tuesday, but this is uncertain
through 18Z so will keep the flow WNW for now.
Elsewhere: Quite a range in ceilings is being observed at issuance
time, with LIFR at KHKY with scattering VFR cigs at KAND and IFR to
MVFR in between. Anticipate slow improvement throughout the region
through late afternoon and this evening as the low pressure system
pulls away. The main exception could be KAVL where improving NW flow
moisture may help hold MVFR ceilings in place most of the night.
Anticipate the gradient tightening and WNW to NW flow developing
throughout, with late afternoon gusts across the western Upstate of
SC and strong gusts right through tonight at KAVL. Expect any
lingering drizzle or occasional rain showers to pull east with the
low pressure system through late afternoon, except lingering VCSH
near KAVL. The pressure gradient will slowly start to relax near the
end of the period.
Outlook: Dry conditions are expected late Tuesday into Wednesday.
Brief moisture return is possible ahead of the next cold front
Wednesday night into Thursday, with colder air and NW flow moisture
setting up by late week into the weekend.
18-24Z 00-06Z 06-12Z 12-18Z
KCLT High 90% High 80% High 100% High 100%
KGSP High 90% High 100% High 100% High 100%
KAVL Med 79% Med 78% Med 73% High 86%
KHKY Med 69% High 90% High 100% High 100%
KGMU High 91% High 100% High 100% High 100%
KAND High 99% 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 from 6 PM this evening to noon EST Tuesday for