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480
FXUS62 KGSP 191800
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
100 PM EST Sat Jan 19 2019

.SYNOPSIS...
A strong low pressure will cross Tennessee today and reach New
Jersey early Sunday morning.  The associated strong cold front moves
from west to east across our area tonight. Strong northerly wind on
Sunday will make temperatures feel much colder. The wind will
gradually diminish Sunday night with a clearing sky.  Another low
pressure system is expected to impact the region on Wednesday and
Thursday.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 1250 pm: Rain shield continues to gradually overspread the area
from the west and SW, and steady ramping up of pops from west to
east throughout the afternoon into the evening still seems to be the
right idea. Weak/in-situ cold air damming is more or less stuck in
place across the area with little evidence of warm sector/southerly
surface flow intrusion into the area. This should gradually change
this afternoon into the evening, as southerly gradient continues to
intensify across the Southeast.

Latest 12Z guidance doesn`t offer much of anything new regarding
threats later today. The very strong/deep meridionally-oriented
forcing depicted along surging cold front and very strong (50+ kts)
0-1 km shear are certainly alarming, and would be a red flag for
high shear/low CAPE severe convective potential IF there was even a
modicum of instability present. However, short term guidance remains
insistent in shunting ribbon of very low sbCAPE south of the
forecast area. Nevertheless, there will probably be plenty of
interesting convective features within the frontal band that will
need close monitoring late this afternoon/evening. Also could not
rule out some isolated damaging winds from showers bringing down the
60kt+ momentum from aloft via plain old convective mixing.

Otherwise, mountain gradient winds will ramp up in the warm
advection this afternoon, and a high elevation Wind Advisory remains
in effect above 3500 feet for the southern NC mountains. Locally
excessive rainfall will be possible tonight, with the biggest threat
in the southern mountain upslope areas where localized two inch
storm QPF totals are possible. With river forecasts a bit below
flood stage, and 3-hr FFG values on the order of 2.75 to 3 inches, a
Flood Watch will not be posted yet. But, one could be needed later
if QPF rises any.

Snow levels will quickly plunge across the mountains from the west
09Z to 12Z behind the frontal passage. There could be a brief window
of mixed ptypes across the mountains, but with solid snow supported
in the W to NW upslope flow areas from 12Z Sunday morning onward.
The upper trough axis will cross the region from the west circa 18Z
Sunday, and the peak cold advection winds will develop. Another
mountain wind advisory could be needed on the cold advection side of
things Sunday, but will handle the warm advection part first this
morning. Outside of the mountains, mid-level dry air will wrap in
quickly Sunday morning to rapidly end PoPs from the west. The
northwest flow upslope snow period will be intense and cold. The
short-lived nature of the event Sunday will be a limiting factor on
snow accumulations, but there is also strong evidence of a Great
Lakes moisture connection to parcels arriving in the NC mountains.
Advisory-level snow accumulations will be a possibility across the
TN border counties and the higher ridges by late Sunday. A Winter
Weather Advisory could be needed for the NC mountains at some point,
particularly with the flash freeze potential with temperatures
falling quickly into the 20s across the mountains through the day.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 300 AM Sat: Very cold high pressure will continue to filter
into the area Sunday night, with the pressure gradient still sharp
across the mountains at the start of the period. Temperatures in
the upslope layer will have already cooled enough that despite the
moisture having become rather shallow, any moisture that remains
will be at favorable temperatures for snow crystal production. So
some very light additional snow accumulation is possible, though
with such small QPF output even the most favored areas only look
to get a couple tenths after 00z. Flurries however may be seen in
the mtns thru early Monday morning.

The gradient will weaken gradually overnight, and while winds will
diminish to unremarkable speeds east of the mtns by the wee hrs
Monday morning, brisk northwesterly winds/gusts will continue across
the higher mountain elevations into the day. Looks like this will
be the coldest morning of the season so far in the mountains and NW
NC Piedmont, and likely at least the more sheltered spots across
the Charlotte metro area and the GA/SC zones. Exceptionally cold
850mb temps bottom out below -15C over the northern mtns. These
are expected to result in sfc temps in the single digits there,
which combined with the continuing wind will produce wind chills
below -5F across much of the zones. Current thinking is that this
hazard is likely to be wrapped into an eventual Winter Weather
Advisory along with the precipitation-related threats. A few power
outages from brisk wind gusts are possible early Monday to boot.

Downslope flow and sunshine occurring Monday will only be able
to bring temps back to within 10-12 degrees of normal over most
of the area, though winds will abate with the center of the high
drifting nearer the area. By Tuesday it will have centered over
the Mid-Atlantic coast, and return flow will get underway in the
midlevels; the last hour of the NAM suggests it may be hanging
on to CAA a bit longer, lending some uncertainty to max temps
Tue. Temps still are expected to moderate gently, a few degrees
warmer than Monday. Clouds will increase late in the day, but no
PoP is expected prior to 00z Wed.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
As of 130 AM Saturday: Starting at 00Z Wednesday with cold high
pressure centered near Cape Hatteras and the next cold front
crossing the Mississippi Valley. Southerly low level upslope flow
will initiate showers over the higher terrain from near Clayton GA
to near Table Rock and Caesars Head SC.  This low level flow will
gradually turn more SW on Wednesday and decrease the upslope effect.
Areas of low pressure and good Gulf moisture helps to enhance
rainfall rates from late Wednesday into early Thursday. The current
EC has the main low tracking slower than the GFS and nearly up the
mountain chain. One to two inches of rain for the event may be
conservative. Still very little if any instability with the EC
having a 100 or less CAPE early Thursday PM. The GFS has all precip
ending at 18Z Thursday while the EC delays it til Thursday evening.
The EC maintains a brief NW Flow event into Thursday night but ends
that by Friday morning.

A clipper type system rapidly approaches from the NW Friday night
into Saturday. Timing differs in the models as the GFS brings this
quick shot of snow across our forecast area early Saturday while the
EC has an evolving larger system Saturday night. The EC has a deep
cold vortex passing just north of our area late in the weekend. We
have a while week to sort this out.

Temperatures are forecast to be several degrees above normal into
Thursday. Max Temps fall below normal Friday and Mins around normal
late in the week.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
At KCLT and elsewhere: LIFR cigs along with IFR/LIFR (and in some
spots VLIFR) visby have settled over the forecast area this
afternoon in response to weak cold air damming. The boundary between
cold air damming conditions and warm/humid conditions will attempt
to lift north in response to increasing southerly flow in advance of
strong storm system/associated cold front. This would be accompanied
by improving flt conditions as well as gusty southerly winds, but
timing this is going to be very tricky. As such, LIFR conditions are
forecast to persist until at least 00/01Z. While some improvement to
MVFR is forecast at that time, widespread moderate rain, with
periods of light and heavy rain will become widespread across the
terminal forecast area this afternoon into the evening, and is not
expected to end at most terminals until late evening or the early
part of the overnight.

Isolated TS are possible this evening, but confidence is too low to
include a forecast mention attm. Additionally, low level wind shear
is expected at most terminals, as a very strong jet core just above
the surface translates across the area. Strong cold front blasting
through the area will begin clearing skies while turning winds to
the NW and seeing them become quite gusty between 09 and 12Z, with
gusts in excess of 30 kts appearing likely at KAVL, and more like
15-25 kts at the other terminals.

Outlook: Windy conditions and cold temperatures will continue into
Monday. The next storm system approaches by mid-week.

Confidence Table...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       Med   75%     Med   75%     Med   64%     High  88%
KGSP       Med   61%     Med   67%     Med   76%     High 100%
KAVL       Med   78%     High  84%     Med   73%     High  94%
KHKY       Med   68%     Med   65%     Med   60%     High 100%
KGMU       Med   66%     Med   69%     High  80%     High 100%
KAND       Med   76%     High  81%     High  80%     High  99%

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:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...Wind Advisory until 10 PM EST this evening for NCZ051-052-058-
     059-062>064.
SC...None.

&&

$$
SYNOPSIS...DEO
NEAR TERM...HG/JDL
SHORT TERM...Wimberley
LONG TERM...DEO
AVIATION...JDL