Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 130804

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
304 AM EST Mon Nov 13 2017

Dry conditions will persist into the middle of the week as
an area of cool high pressure lingers over the region. A general
warming trend will begin mid-week and continue through Friday. A
cold front is expected to cross the region Saturday with cool and
dry high pressure returning on Sunday.


As of 200 AM EST Monday: Elongated surface ridge/damming remains in
place down the Eastern Seaboard, though the parent high continues to
move off the SE Canadian coast, leaving us in just a residual cool
pool with shallow moisture at the surface with a weak inversion atop
the cold dome. A sharp shortwave and associated front is working
its way across the Appalachians at AFD time; the pressure field is
ill-defined across the southern mountains as can be typical but it
should cross into the Piedmont by mid-morning, scouring out the
damming. Also as is typical, with out the low-level CAA and with
increasing sunshine, temperatures behind the cold front will be
warmer than what we`ve seen in the damming the past couple of days.
The shortwave will slide off the East Coast this evening with high
pressure over the upper OH Valley in its wake. Another dry shortwave
will push toward the area by the end of the period bringing a weak
reinforcing front with us to cool us down into the short term.

For today, morning clouds/fog/drizzle will continue but improvement
will begin by mid-morning. Until then, possibility still exists that
we may need a Dense Fog Advisory later this morning; right now
visibilities are generally in the 1-3 mile range, but a couple of
obs across the Upstate are beginning to drop to 1/2 or 1/4mi. The
light winds across the Piedmont will help contribute to this
potential, but timing will be critical with the front coming in
which will begin increasing winds through the morning. At this point
not enough confidence to issue but will continue to monitor.

Models typically erode damming too quickly and new bufr soundings
are wanting to hold onto very shallow moisture until early afternoon
across the CLT area, so confidence on exact timing of improvement
isn`t particularly high. NW surface flow behind the front (complete
with gap winds, though the gradient isn`t all that impressive) will
help to clear us out as well. In the end, by this afternoon we
should have mostly sunny skies in place, and with the downsloping
off the escarpment this will allow temperatures to rise to just a
handful of degrees below seasonal normals. A little cooler tonight
than what we`ll see this morning, just with the slightly drier
airmass and clear conditions.


As of 255 AM EST Monday: the short-term fcst picks up at 12z on
Tuesday with a weak upper shortwave approaching the fcst area and
ridging still in place over the Western CONUS. The shortwave will
move over the CWFA Tues afternoon and offshore by early Wed. In
its wake, the upper-lvl pattern will flatten over the region while
an upper trof amplifies over the Great Lakes. At the sfc, broad
high pressure will be centered to our north to start the period.
As we move into Wed, another cold front will approach the area
from the west and move thru the CWFA early Thurs. The latest model
guidance has the front moving east of the fcst area by the end
of the period, 12z Thurs. As for the sensible wx most of the
period should be dry with PoPs increasing into the chance range
after roughly 00z Thurs as the front moves into the higher terrain.
By 12z Thurs, precip chances have already begun to wind down.
Any QPF should be minimal with fairly weak upper-lvl support and
shallow moisture present. Temps will remain a few degrees below
climatology through the period.


As of 215 AM Monday: Only modest changes were made to the going fcst
grids. The op models agree well during the first half of the period
when ulvl ridging dominates the pattern...and they continue to
diverge in their solns over the weekend into early next week. Thu
will be the warmest day with max temps reaching a couple degrees
above normal with llvl w/ly winds adding an additional warming
component. There may be some lingering -shra across the wrn NC mtns
in the morning as a weak front lifts toward the NE COUNS. Expect
clearing conds overnight with ulvl heights increasing while sfc
ridging prevents any sigfnt moist adv. A similar day is in store
Fri...however winds become aligned more ne/ly and e/ly as a Canadian
high center moves down the east coast...likely hold max temps below
normal by a couple degrees.

Things become more dynamic Fri night as a cold front is progged by
the GFS to reach the NC mtns and push to the east by early Sat
afternoon. This front will have a good amount of moisture with it
and increasing bulk shear...however instability will be very low due
to the early timing and expected cloud cover. PoPs will be held in
the mid/high chance range with this system as the ECMWF continues to
be a 12-18 hr slower soln...thus confidence remains below avg. There
is -snsh and -rasn mix in the fcst over the NC mtns Sat night...but
will keep accums very low-end due to thermal uncertainty with the
system. By Sun...a very dry area of high pressure builds in and
lowers sfc td/s into the lower to mid 20s and PWATs drop below 0.25
inches thru Mon. Sfc RH values come close to FDS levels and profiles
suggest the potential for moderate gusts Sun afternoon...however
10/100 hr fuel moisture will likely be a little too high for fire wx
concerns...however this situation may change. Max temps on Sat will
reach arnd normal levels depending the FROPA timing...then drop a
couple cats below normal on Sun with a true cP airmass change.


At KCLT and Elsewhere: Complicated forecast for the next few hours
with cold air damming persisting but weakening. Widespread IFR to
LIFR expected overnight, with areas of DZ/FG developing as well.
Have continued trend of handling some of the lowest restrictions in
a TEMPO. All guidance erodes the damming fairly quickly after
sunrise and have gone with a slightly more pessimistic forecast, but
in all cases by mid-day expect VFR conditions. Light NE winds at
most sites, more N to NNW at KAVL, and occasionally VRB through the
period (though still favoring N).

Outlook: Drying conditions will keep the area generally free of
restrictions Monday night through Wednesday. The only exception
could be mountain valley restrictions around daybreak each morning.
Another front will move into the region from the northwest Wednesday
night into Thursday, but with rather limited moisture.

Confidence Table...

            08-14Z        14-20Z        20-02Z        02-06Z
KCLT       Med   63%     High  81%     High 100%     High 100%
KGSP       Med   68%     High  98%     High 100%     High 100%
KAVL       Med   72%     High  91%     High 100%     High 100%
KHKY       Low   44%     High  97%     High 100%     High 100%
KGMU       Med   68%     High 100%     High 100%     High 100%
KAND       Med   71%     High  86%     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:




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