Area Forecast Discussion
Issued by NWS Greer, SC
FXUS62 KGSP 230848
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
348 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 330 AM EST Monday: A rather dynamic/stacked system continues
to slide east across North GA into the Western Carolinas at
this time, which is highlighted by a 537dm low atop a 988mb
surface low. Latest WV imagery indicates drier air wrapping
in across the Carolinas ahead of the primary surface cyclone,
behind the remnant line of convection that is pushing into/thru
Western NC which is associated with a warm front. Winds behind the
front and said convective band have veered swly, while winds hold
nely out ahead. Precip rates have tailored off over the last few
hours, however training of multiple rounds of convection have led
to a few stream rises across portions of the Upper French Broad
Valley, as well as in CLT metro where McMullen and Briar creeks
have approached/exceeded their banks. Fortunately the heaviest
bands of convection are on the move out of town thereby allowing
said streams to crest, thus current warnings/advisory will likely
be allowed to expire on schedule.
Pops through the morning will taper from south/north as the
convection associated with the warm front moves north into VA.
That said, will hold pops at slight/chance levels across the low
terrain through mid afternoon as WV imagery favors additional
upstream moisture, which combined with weak instability and
deformation zone forcing, prompts guidance to suggest light showers.
Pops are finally allowed to lower to non mentionable levels across
Northeast GA and the SC Upstate by mid/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 today 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.
Lastly, the aforementioned nwly flow will become quite gusty behind
the departing wave, thus will issue a wind advisory for the entire
mtn chain running from 6PM this evening through noon on Tuesday.
Impacts will mostly be felt at the highest elevations above 3500ft,
however significant gusting of 45-50mph 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 /09Z MONDAY THROUGH FRIDAY/...
At KCLT and Elsewhere: A mixture of VFR/MVFR and IFR through the
evening/morning at all sites as bands of shra/tsra move through
the region associated with a large upper low pressure system
sliding through north AL/GA at this time. Multiple round of
convection can be expected at most sites through daybreak, however
the SC sites will likely see the least amount of shra/tsra given
current placement and little if any activity to the west. Thus,
prevailed shra with vcts at the SC sites with MVFR/VFR cigs/visb,
with all weather removed by around 08z. As for the NC Sites,
expecting continued convective activity along with vary degrees
of cig/visb restrictions through the night, with all wx removed
around 11z-12z. Winds will remain backed to the e/ne and gusty
ahead of the tailing line of convection that is currently just west
of I26, with all sites west of said line veered sly and slightly
weaker however still with a few gusts. Generally, expecting a
period of MVFR after any shra exits the region, before conditions
lower further into the IFR/LIFR range as the very moist PBL settles
leading to patchy fog and low stratus. Otherwise, a final round
of deformation zone showers is possible behind the departing upper
low this afternoon therefore all sites feature prob30s for such.
Cigs will finally recover late in the day at all sites, as winds
veer further to the nw and get quiet gusty.
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.
08-14Z 14-20Z 20-02Z 02-06Z
KCLT High 82% Med 75% Med 76% High 100%
KGSP Med 69% Med 69% High 88% High 100%
KAVL Med 79% High 89% High 82% Med 79%
KHKY High 86% Med 69% Med 75% High 89%
KGMU Med 77% Med 69% High 90% High 100%
KAND High 93% High 80% 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