Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 180252

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1052 PM EDT Thu Oct 17 2019

A dry and chilly airmass will remain over the area into
Friday. Deep moisture returns over the weekend as a potential
tropical cyclone moves from the Gulf of Mexico toward the eastern
Carolinas. Brief drying returns for Monday before a sharp cold front
crosses the area on Tuesday.


As of 1045 pm: Confluent upper flow downstream of a ridge will permit
a dry sfc high to migrate steadily toward the East Coast over the
next 24 hours. With skies virtually clear and a diminishing pressure
gradient, winds should become light across the entire region
overnight. This implies good radiative cooling and another chilly
night. Partial thickness trends will be slightly higher than they
were last night, however, which will offset the cooling a bit. This
morning`s mins turned out to be a tad colder than expected, even
where winds stayed up overnight. Thus we will continue to hug the
low end of the guidance range, and fcst lows in the 30s throughout
the mountains and even into the I-40 corridor of the NC Piedmont.
Frost will be common in the area where we already had a Frost
Advisory, but it now appears some of the adjacent foothills zones
and far NE GA will see abundant frost, too. Therefore the Advisory
is being expanded slightly. Most of Mitchell and Yancey counties in
NC are fcst to fall below freezing, so a Freeze Warning continues
there. In addition, Haywood County has been an especially cold spot
in recent mornings, and see no reason why Friday morning will be
different. As such, min temps have been decreased there by a couple
of degrees. Although there probably isn`t a lot of usefulness to it
at this point, that zone has been upgraded to a Freeze Warning.
Patchy frost is also possible in the I-40 corridor and even outlying
areas of the northern Charlotte metro.

Friday looks quiet weather-wise, likely starting off
cloud-free. Temps should top out a couple degrees below normal
despite the sunshine. Scattered high clouds should begin to spread
in late in the day ahead of the incipient Gulf low.


As of 254 PM Thursday: Any time you throw a potential tropical
cyclone into the mix...the fcst is put into a state of flux...and
that is the case for this weekend. The operational GFS and ECMWF
are in relatively good agreement with the official track fcst from
NHC for the Gulf system, which lends enough confidence to make some
substantial changes starting Saturday. It still looks like the
leading edge of any precip shield will not reach SC by daybreak
Saturday, so the Friday night period will stay dry. However, the
guidance shows a steady progression of the precip shield on the
leading edge of the system moving northeast across the fcst area
on Saturday such that all our area stands a good chance of seeing
rain by sunset Saturday. Precip prob has been raised by blending
in the very high probs seen in the model blends. Temps are trending
cooler, so the day now looks cool, breezy, and wet. The track takes
the center of the storm, such that it will be having already most
likely made a transition to extratropical, past to the southeast
Saturday night. The storm will be ragged and the wind field on the
NW side is likely not to be of much significance as it currently
stands. The precip should start to cut off from the southwest by
daybreak Sunday, so we also have substantial changes with precip
prob on the back end. Latest thinking is that we should be able
to salvage Sunday afternoon with clearing sky and dry air coming
back from the NW as high pressure builds in. Precip amounts will
be enough to be beneficial and most likely not enough to cause
any problems, but this could change if the path of the system
shifts leftward.


As of 220 PM Thursday: The main weather story for the long term
period will be a vigorous cold front passage early next week. The
setup includes a flat upper ridge in place over the southeast Sunday
night as the departing tropical low moves east over the Atlantic.
Meanwhile, a closed low pressure system will develop from the
Rockies to the central Plains. The resulting full latitude trough
will sweep east through the Mississippi River Valley Monday into
Monday night and push the aforementioned sharp cold front toward the
southern Appalachians. Timing differences remain among the models,
with the GFS about 12 hours faster with the surface cold fropa than
the ECMWF. A consensus approach will bring the cold front to the
southern Appalachians Tuesday morning, and then quickly across
the region by early to middle Tuesday afternoon. This is highly
subject to change. This timing will serve to limit instability
somewhat, but still anticipate enough CAPE for thunder over at
least the southern half of the area, with the strongest overlap
of instability and shear along the eastern Piedmont. It`s quite
possible that the 850 mb jet will ramp up into the 40 to 50 kt
range just ahead of the front, so the potential for severe
weather will need to be closely monitored.

Breezy to windy conditions are likely in the mountains late Tuesday
through Tuesday night with a tightening pressure gradient in the
northwest flow cold advection behind the front. Zonal flow aloft and
surface ridging will redevelop Wednesday behind the departing trough
before heights start falling again from the west ahead of the next
trough axis digging through the Plains on Thursday. Anticipate above
climo temperatures ahead of the front, then below to near normal
temperatures following fropa from Tuesday night onward.


At KCLT and elsewhere: VFR/mostly SKC conditions will persist
through the period. Winds will be primarily light northerly tonight.
Winds will gradually veer toward the NE early Friday as sfc high
migrates from the Ohio Valley to the East Coast. Winds may become
light S/SW by the end of the period.

Outlook: A Gulf low pressure system will likely produce another
round of rain and associated restrictions, along with gusty winds
Saturday through early Sunday.

Confidence Table...

            03-09Z        09-15Z        15-21Z        21-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     High 100%     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:


GA...Frost Advisory until 9 AM EDT Friday for GAZ010-017.
NC...Freeze Warning until 9 AM EDT Friday for NCZ049-050-052.
     Frost Advisory until 9 AM EDT Friday for NCZ033-048-051-053-


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