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000
FXUS62 KGSP 120755
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
355 AM EDT Fri Apr 12 2024

.SYNOPSIS...
Drier air will filter into our region this morning with a secondary
cold front. Very windy conditions also will develop and continue
into Saturday. Dry and warm weather returns for the weekend into
the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 330 AM: 986 mb sfc low now centered over Lake Erie
beneath expansive and correspondingly deep upper trough. At this
hour we are between vort lobes or embedded shortwaves
encircling the upper low. Precip has mostly exited the I-77
corridor while a few light returns are beginning to reach the NC
mountains ahead of the second shortwave. Upslope NW flow is
generating cloud cover over the mountains. Any accumulating
precip early this morning likely will be confined to the TN
border area, but a sprinkle or two really can`t be ruled out
anywhere. Wind Advisory went into effect for the mountains; most
of the automated sites continue to report gusts at this hour,
with sfc cooling being limited by the gradient wind and fairly
mixed low level profiles permitting some gusting. Expect the
gusts to pick up rapidly after daybreak and peak above 30 kt in
virtually all of the CWA this afternoon. For the mountains, the
setup does not change significantly through tonight; gradient
does not relax soon enough to allow gusts to taper off at
sunset. Hence we are expanding the mountain advisory through
Saturday morning.

Northwest flow will continue across the mountains through tonight,
but the sfc layer will dry out a bit this morning, with profiles
more mixed than usual. As lift increases with the second vort max
and lapse rates improve above the PBL, shallow convection becomes
possible, and some moisture returns in the midlevels. Thus the
upslope lift is expected to result in convection by late morning,
and PoPs/clouds amplify accordingly. Temps should be warm enough
for the daytime activity to be all rain in the high elevations. As
the wave passes over the Piedmont the same effect occurs, and a
small PoP is included in the NC Piedmont. However, with strong
downsloping the mixed layer will be very deep, possibly up to
700 mb or higher in some spots. That suggests the precip that is
generated may not reach the ground, but adds the potential for peak
gusts of 40+ kt. This exceptional mixing looks most likely in our
Savannah River Valley and western Upstate, so Wind Advisory will be
expanded there for the afternoon only. The NC Piedmont convective
layer is depicted as having as much as 200-400 J/kg of CAPE on some
guidance, considerably more than in a run-of-the-mill event of this
nature, which backed up the idea of PoPs. This convection looks
to occur in air cold enough to generate some ice nuclei aloft,
and a few spits of graupel could reach the ground. Even if not,
the melting or sublimation could further enhance wind gusts. We and
our neighboring offices will have to monitor winds this morning
and further expansion of the Advisory cannot be ruled out. Temps
will be much cooler today but the downsloping will keep them on
the warm end of guidance in the Piedmont. Tonight, some NW flow
precip chances do continue until midnight or so. High elevations
might see rain change to snow briefly before ending, most likely
without any accumulation.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
As of 228 AM Friday: A deep negatively tilted longwave trough will
be quickly lifting northeast and off the coast of New England on
Saturday with broad northwest flow continuing across the Southern
Appalachians. The airmass will be exceptionally dry and moisture
starved, thus no upslope showers are expected across the mountains.
Low-level temperatures will begin to warm with airmass modification
well underway amidst continued deep mixing to 800mb. This will
foster high temperatures in the low to mid 70s across much of the
area. The primary focus on Saturday will be increasing fire weather
issues as some degree of gusty winds will continue to mix down,
especially earlier in the day before the core of stronger winds pull
away with the upper trough. A deep and well mixed PBL will support
very low RH values in the upper teens to low 20s across the
foothills and Piedmont. Fire products may eventually be needed for
portions of the area on Saturday, especially where spring green up
hasn`t completely finished. By Sunday, deep-layer flow will quickly
become quasi-zonal as a northern stream shortwave trough passes by
to the north. Any showers should remain focused off to our north
across the Ohio Valley in the vicinity of an attendant surface cold
front. Warming of the airmass will continue unabated with highs
cracking the low to mid 80s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 241 AM Friday: Heading into early next week, the synoptic
pattern will undergo modest amplification as a potent compact trough
dives into the Desert Southwest on Monday and ejects into the
Southern Plains on Tuesday. This will in turn result in a
strengthening downstream ridge across the Appalachians with rising
heights and warming low-level temperatures. Afternoon highs are
expected to soar into the low to upper 80s Monday and Tuesday with
mild overnight lows in the upper 50s to low 60s. By midweek, the 12z
suite of global model guidance is in generally good agreement that
the Southern Plains closed upper low and associated trough will lift
northeast into the Midwest. In this solution, the Carolinas and
northeast Georgia will be displaced well south of the greatest
forcing for ascent with only subtle height falls across the region.
A trailing cold front extending along the Ohio Valley to the Lower
Mississippi Valley will quickly become oriented parallel to upper
flow with little eastward progression as the wave quickly lifts into
the Great Lakes. A general dearth of forcing will limit any sensible
weather across the area with only a slight chance for a few showers
to graze the mountains on Wednesday. A northern stream trough
emerges from the northern Rockies late week and should provide
enough forcing to drive a cold front towards the area around next
Friday. Guidance quickly diverges, however, with regards to the
strength and evolution of the wave. Regardless, warm temperatures in
the 80s will likely continue until the arrival of the late week
front.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Very spotty -SHRA really can`t be ruled out
at any site early this morning but chance too small to mention,
potential impacts being brief MVFR cig if a shower passes over. The
MVFR chance will become increasingly less likely with low-level
drying toward dawn. Winds will be the main concern thru the
period. Strong gradient on southern periphery of sfc/upper low
will offer abundant strong wind aloft, along with very deep mixing
potentially above 700mb. Gusts likely will continue through sunset
today and might even last through much of Friday night. Uptick
should occur after dawn, with peak afternoon values likely near
40 kt at all sites, likely 45-50 kt at KAVL. KAVL should remain
NW`ly thru the period. The winds mixing down will be W to WNW but
low-level flow may back in advance of embedded shortwave passing
this afternoon. KCLT is likely to experience a near-crosswind
most of the day, but not likely flip NW for good until very late
afternoon. High-based congested or towering cu will be possible
this afternoon as shortwave provides a parting shot of forcing,
potentially producing brief -SHRA esp at KCLT and KHKY, enhancing
gust potential but probably no other impact.

Outlook: Wind gusts will gradually taper off Friday night east
of the mountains, but will remain gusty across the North Carolina
mountains through Saturday. VFR conditions will persist this weekend
and early next week as high pressure builds across the terminals.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Wind Advisory from noon today to 8 PM EDT this evening for
     GAZ010-017-018-026-028-029.
NC...Wind Advisory until 10 AM EDT Saturday for NCZ033-048>050-052-
     053-059-063>065-501-503-505-507-509.
SC...Wind Advisory from noon today to 8 PM EDT this evening for
     SCZ010-101>107.

&&

$$

SYNOPSIS...Wimberley
NEAR TERM...Wimberley
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...Wimberley