355
FXUS62 KGSP 170738
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
338 AM EDT Fri May 17 2024

.SYNOPSIS...
A warm front and weak low pressure system will bring frequent
chances for showers and thunderstorms today through the
weekend. Somewhat drier conditions return early next week resulting
in only isolated afternoon and evening showers and storms Monday
and Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 300 AM Fri: Broad area of upper divergence will shift east
out of the lower Mississippi Valley this morning, associated with
jet streak and shortwave south of the Great Lakes. Meanwhile,
weakening MCS will move along the Gulf Coast. Abundant cirrus
are creeping in our direction and should follow the upper ridge
axis. Think these cirrus are filling in too slowly over our area
to have a big impact on morning mins; at least patchy fog may
develop near the major rivers by daybreak.

Vort maxes from the Gulf Coast convection look to advect northeast
to our vicinity later this morning, along with cooler air at 700
mb. Prog soundings show MUCAPE ticking upward to match within a
relatively shallow layer, and CAMs variously develop a wave of
showers from around midday and early afternoon, although they are
not in particularly good agreement as to where this occurs. Thunder
appears isolated at best with this activity owing CAPE being
relatively shallow and at warm temps. Light and increasingly
moist low level southerly flow will develop and could produce some
light precip near the SW NC mountains or Escarpment as well. Thus
PoPs increase a bit faster than we had previously advertised,
still mainly focused over the mountains at onset. Meanwhile, warm
front will shift northward thru the Deep South, associated with
developing sfc low in MS/AL. The approach of this front warrants
further increases in PoP and expansion across the rest of the
CWA in the afternoon, with likely to categorical chances for the
whole area by late evening. This second round of precip is more
likely to induce thunder, particularly in our southern half, with
deep convection possible albeit most likely elevated from the warm
frontal inversion. This MUCAPE appears meager enough that severe
wx looks unlikely. Peak PoPs will follow the warm front, behind
which moist layer becomes more shallow albeit with weak upglide
continuing. Low stratus are likely to develop in the evening and
persist into Saturday; unclear at this time whether the end of
precip will be associated with fog formation but a mild, muggy night
appears a good bet. WPC Marginal Risk seems to adequately cover
the area most likely to see convective rainfall rates thru tonight.

The clouds and showers will keep temps a few degrees below normal
in the west, but still may rise a degree or two above normal in
the east where these are less of a factor.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 245 AM EDT Friday: A positively tilted southern stream
upper trough will cross the TN valley on Saturday providing some
QG forcing atop the FA during peak heating. Precip from Friday
night may cause a frontal boundary to set up roughly along or just
north of the I-20 corridor early Saturday. The air mass south of
the boundary will be fairly unstable along with good bulk shear of
40-50 kt. For our forecast area, CAPE looks to be 1500 J/kg or less,
with the various deterministic models showing the maximum sbCAPE in
differing parts of the area. Shear will also not be quite as high
as to our south. So this muddies the severe threat quite a bit. The
latest CAMs show a rather disorganized convective mode across the
CWFA Saturday, and a marginal risk in the SPC Day 2 Outlook seems
reasonable. With more convection expected to our south, and veering
deep-layer flow to nearly due westerly, will also limit excessive
rain potential, as PWATs trend down. Despite plenty of cloud cover,
highs will be near normal with humid low-mid 60 dewpts.

The low pressure system slows down once it reaches the NC Coast
Sunday morning, with the CWFA in the NELY-flow side of the
system. Wrap-around moisture should keep skies cloudy to mostly
cloudy with showers and mainly general thunderstorms possible. The
air wrapping around the system should be less unstable and bulk
shear will generally 20 kt or less, so severe thunderstorm chances
will be low. Heavy rain may localize along the escarpment with
nearly parallel deep-layer flow and some ELY upslope, but overall,
no strong signals for excessive rainfall/flooding. Highs will be
kept below normal, especially across the NC foothills and Piedmont.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 315 AM EDT Friday: The low pressure system along the NC coast
should drift far enough east to allow more dry air to work into the
forecast area from the N/NE on Monday. This should allow for more
breaks in the clouds and lower precip chances. With more insolation,
could see diurnal convection across the mountains, with isolated
showers possible across the Piedmont, but severe storm threat
should remain low. Temps will be slightly below normal thanks to
continued cool NELY flow. High pressure builds in Tuesday, making
for largely dry wx across the area and temps returning to normal.

The 00z medium range guidance has come into better agreement on the
next cold front to affect the forecast area. Earlier guidance had
moisture and PoPs returning Wednesday, but now have backed off. So
Wednesday may end up being dry with temps warming to slightly above
normal. With an upper ridge building over the Southeast, the front
will weaken as it tries to push into the area Thursday. The 00z
guidance shows meager QPF response with the front, and isolated
to scattered convection is expected. The NBM PoPs may be a little
overdone, if this trend holds, but for now will keep the solid chc
PoPs in there. Slightly above-normal temps will continue thru the
end of the week.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Relatively low confidence TAFs with multiple
sources of weak forcing and differing signals among guidance
members. Cirrus will increase early this morning but deck does not
look likely to fill in quickly enough to keep radiation fog at bay
in the river valleys. TEMPO MVFR vsby and SCT002 for KAVL, but the
other sites chance of fog small enough to omit. Lapse rates will
improve after daybreak with arrival of weak shortwave preceding
sfc/upper low in the southern Plains. This is expected to spawn
scattered SHRA/TSRA in the late morning to early afternoon which
has prompted TEMPO impacts earlier in the day than usual. Such
convective development is likely to result in spotty low VFR cigs,
aside from the higher cloud decks thickening. This activity may
weaken or become more isolated before more widespread precip and
perhaps embedded TSRA arrive with warm front tonight. Warm front
appears likely to produce MVFR and then IFR cigs tonight, with
areas of fog developing after precip. Generally southerly winds
this period.

Outlook: Periods of convection, which could be widespread at
times, are expected through the weekend. Late night/early morning
restrictions in low stratus and/or fog will also be possible. Drier
weather is expected to return early in the next work week.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$

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