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fxus62 kgsp 200130 

Area forecast discussion
National Weather Service Greenville-Spartanburg SC
830 PM EST Tue Nov 19 2019

dry high pressure will return seasonal temperatures to the region
through Thursday. A cold front with rain showers will cross the area
Friday into Saturday.


Near term /through Wednesday/...
as of 828 pm: minor adjustments made to pops/wx/temperatures to
coincide with latest trends. Latest radar imagery depicts a
batch of light showers that have broken containment and are
currently pushing eastward over the northern foothills, towards
the I-77 corridor. Per latest available obs, only light
rain/drizzle is reaching the ground attm. Current temperatures
are running a few degrees warmer than expected, especially
across the mountains. As a result, the potential for a rain/snow
mix and snow amounts across the higher elevations over the next
few hours has decreased, though still remains a possibility
through tonight.

Previous discussion: as low clouds continue to thin and scatter from
west to east, an area of mid-level clouds has begun to overspread
the area in association with an upper speed Max digging into the
base of the long wave trough. This feature will pass over western
North Carolina this evening with little fanfare. However,
accelerating northwest flow in its wake will yield increasing
chances for upslope showers near the Tennessee border. Snow levels will be
quite high, but some flakes may mix in with any rain above 3500',
while light accums (2" or less) will be possible above ~5000'.
Upslope shower chances reach a nadir (30-50%) around midnight, with
depleting moisture resulting in steadily decreasing pops to a slight
chance or less by sunrise. Wouldn't completely rule out another
round of low stratus/perhaps fog developing tonight, esp across the
Piedmont. However, slightly drier air and mid-level cloud cover is
expected to preclude a repeat performance. Min temps will again be
very close to climo.

Wed morning will see steadily decreasing northwest flow cloud cover, with
all areas expected to see sunny skies by late morning/early
afternoon. Max temps are forecast to be in the ballpark of climo,
really for the first time in over a week.


Short term /Wednesday night through Friday/...
as of 1254 PM tuesday: the middle part of the week looks
exceedingly quiet as a progressive upper ridge pushes a sfc
high overhead Wednesday night and then off the southeast coast on
Thursday. Temperatures will be close to normal as a result. The only
question is whether or not the next system reaches the mtns before
daybreak on Friday. As it stands now, the model guidance takes the
upper trof axis only to the Carolina coast while flattening it,
and keeps all the forcing and deeper moisture to the west of the
mtns through 12z Friday. Most likely, this means a dry Thursday
night even across the mtns, with maybe a small chance of light
precip reaching the smokies around daybreak Friday. Overnight
temps will be almost ten degrees above normal owing to increasing
cloudiness after midnight with the system approaching from the west.


Long term /Friday night through Tuesday/...
as of 203 PM tuesday: the main event for the forecast cycle still
looks like the approach and passage of a srn stream low pressure
system Friday and Saturday. The operational GFS and European model (ecmwf) are in
decent agreement with the fcst evolution of this system. A sfc cold
front connecting a nrn stream low and the developing srn stream
wave should sag down across the mtns and into our region on Friday
as a lead short wave pulls out of the upper low over the plains
and rides over the top of the frontal zone. The short wave will
have deepening moisture to work with so it seems reasonable that
precip will spread in from the west during the day. Think the NAM
depiction is too dry, and even if the European model (ecmwf) is correct in keeping
the sfc front to the north through the afternoon, there is a good
chance that shower activity will develop in the warm sector ahead
of the approaching low. The situation just GOES downhill from
there as low pressure should organize along the front and move
over the Tennessee Valley by daybreak Saturday. Precip prob may continue
to rise overnight, but there is some potential for a lull of sorts
during the Friday night period in the wake of the initial short
wave and the approach of the sfc low. Saturday looks potentially
more interesting as the guidance depicts the sfc low moving over
or to the west side of the mtns. At issue will be our potential to
develop some sfc-based instability east of the mtns in the warm
sector on Saturday afternoon, which both operational models do
to some small degree. If we can eke out a few hundred j/kg, there
will be the potential for a high shear-Low Cape type environment
that could be interesting as the cold front sweeps across the
region late in the day. It's way too early to put too much stock
into this development, but we should be wary as we further refine
the fcst for Saturday through the week. As the front passes and
the low pulls away Saturday night, there is some potential for
a changeover to snow showers at the highest elevations, but the
moisture pulls out quickly with the fast movement of the system,
so the northwest flow potential is small.

Only a slight cool-down is anticipated in the wake of this system on
Sunday as the upper trof moves away quickly while deamplifying. The
rest of the period looks dry with a broad upper ridge building
in with sfc high pressure for Monday and Tuesday, meaning a quick
return to near normal temps.


Aviation /02z Wednesday through Sunday/...
for kclt and elsewhere: VFR currently prevails at all taf sites this
evening. Despite less available low level moisture than 24 hours
ago, could not entirely rule out the potential for patchy fog/low
stratus in and around the kclt area overnight. Latest obs depict fog
development outside of the kclt area, though, given a dewpoint
depression of 6 degrees, do not anticipate fog development at kclt
attm. Did introduce few015 around 8z at kclt to note the possibility
of stratus. Though again, confidence is low attm. The other note of
possible low cigs in the going fcst is for kavl overnight with the
anticipation of upslope shower development across the mountains, and
passing low clouds. Attm, do not anticipate any precipitation or
flight restrictions at kavl. Otherwise, expect VFR to prevail at all
sites through the valid taf period. With light and variable winds
overnight, expect west-northwest winds into Wednesday, 5 to 7 kts.

Outlook: Mountain Valley fog possible Thursday morning, along with
the possibility of increasing precipitation chances and flight
restrictions on Friday and Saturday. Otherwise, expect VFR.

Confidence table...

01-07z 07-13z 13-19z 19-00z
kclt high 100% high 100% high 100% high 100%
kgsp high 100% high 100% high 100% high 100%
kavl high 100% high 95% 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:



Gsp watches/warnings/advisories...



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