Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 231533
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1033 AM 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 TONIGHT/...
As of 1020 AM EST Monday: Surface observations show the 988 mb
surface center moving northeast of HKY this morning with the closed
537 dm 500 mb system pulling east of I-77. Banded showers on the
back side of the system will continue to pull east of the Blue Ridge
through the day, with a NW flow upslope component increasing as well
as the pressure gradient tightens. In addition to minor mid-course
corrections on PoP and Sky, snow amounts have been increased at the
higher elevations above 4500 feet. No snow products should be needed
with any advisory accumulations through tonight likely impacting
only areas above 5000 feet. The mountain Wind Advisory remains
well-placed. We`ll have to closely inspect the 12Z model data to see
if we need a narrow stripe of High Wind near the Blue Ridge tonight.
Otherwise, PoPs are finally allowed to lower to non-mentionable
levels across Northeast GA and the SC Upstate by late afternoon, as
well as the the NC Fthills/Piedmont by early evening. As for the
mtns, increasing northwest flow behind the departing upper low will
warrant likely/cat pops along the TN line through tonight given
upslope shower potential. For the most part, thermal profiles across
the high terrain look warm enough to deter wintry precip concerns,
however cooling aloft will likely allow for a ptype phase change
from rain to snow at the highest elevations tonight and into Tuesday
morning. QPF remains relatively light with this brief nwfs regime,
primarily thanks to the lack of any Great Lakes moisture fetch, thus
total snow accums should remain below advisory criteria for most
areas above 3500 feet. Wind impacts will mostly be felt at the
highest elevations above 3500ft, however significant gusting of
45-50 mph cannot be ruled out below that as well. Temperatures today
will remain just above normal levels, with overnight lows holding
above normal as well.
.SHORT TERM /TUESDAY 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 /16Z MONDAY THROUGH FRIDAY/...
At KCLT and Elsewhere: IFR has lingered a bit longer than expected
this morning as forcing continues under the slowly departing low
pressure system. Weak deformation zone behind the low will keep
showers in the forecast through this afternoon at the TAF sites,
especially KHKY to KCLT. Cigs will finally recover late in the day
at all sites to low VFR, as winds veer further to the nw and become
gusty at the SC sites, less gusting favored at the NC
Piedmont/Foothill sites. Lastly, skies will lift to solid
VFR...perhaps SKC...late in the period as dry air spills in behind
the departing upper low pressure system. NW flow moisture will keep
more clouds at KAVL, though.
Outlook: Conditions will improve on Tuesday as the atmosphere
dries out, all ahead of another cold front that is expected to move
into the region by late week.
15-21Z 21-03Z 03-09Z 09-12Z
KCLT High 96% High 81% High 100% High 100%
KGSP High 81% High 100% High 100% High 100%
KAVL High 81% High 88% Med 76% Med 71%
KHKY High 89% Med 60% High 100% High 100%
KGMU Med 74% High 100% High 100% High 100%
KAND Med 78% 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