488
FXUS62 KGSP 261727
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
127 PM EDT Wed Jun 26 2024

.SYNOPSIS...
High temperatures peak today ahead of an approaching cold front.
Shower and thunderstorm possible over the mountains this afternoon
and chances linger into the weekend. Hot and humid conditions are
expected Friday into the weekend ahead of another cold front
tracking through the area Sunday. Expect slightly cooler
temperatures early next week and an unsettled pattern.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 145 PM Wednesday: Clear skies start to fill in with cirrus and
a non-threatening cumulus this afternoon. Synoptically, an
amplifying area of high pressure out west directs upper flow more
westerly to start. A weak trough makes a run for the south from a
disturbance over the Great Lakes. This extends a cold front from the
north toward the southern states. By this afternoon, the frontal
boundary will be draped across the TN/KY region, progressing toward
the CWA. Meanwhile, a weak warm front recedes southward as moisture
continues to mix out during the afternoon period. Guidance from the
CAMs struggle to initiate convection over the mountains. HRRR and
NAM both suggests minimal shower or thunderstorm activity. Looking
at the modeled soundings from the RAP and NAM, the boundary layer
this afternoon is extremely mixed, with very steep sfc-10km
adiabatic lapse rates. Another limiting factor is the lack of
instability. Guidance paints a picture of only a couple hundred
joules of sbCAPE. These factors, combined with the upper support
lacking ahead of a front, confidence is low for convection today for
most of the CWA. Will still maintain slight chance PoPs (25%-35%)
for the mountains to account for any possible isolated shower or
thunderstorm. For tonight, moisture ahead of the FROPA filters back
into the area as sfc flow becomes more southerly. The boundary
should reach the mountains by daybreak and slowly move through the
CWA. This will increase chances for precipitation on Thursday, but
QPF response is still low. Guidance from the GFS/NAM/Canadian/EURO
all target the higher QPF across the mountains Thursday afternoon,
with limited or none in the SC/NC Piedmont. Overall, the mountains
have a better chance (50%-70%) of seeing showers or thunderstorms
Thursday afternoon and evening, but rainfall amounts will likely be
small. Temperatures today are expected to be the hottest so far this
summer, with high 90s east of the mountains. Given the lower
dewpoints, the heat index should not be as much of a problem, but a
few spots in the eastern portion of the CWA could see 100. Expect a
small dip in highs tomorrow with the FROPA.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 130 AM Wed: A trough will cross the Midwest/Northeast Thursday
into early Friday, with continental high pressure migrating eastward
in its wake. In turn, a weak cold front will just reach the CWA on
Thursday. Most models depict height falls occurring more strongly to
our southwest, possibly as a result of an MCV diving into the Deep
South following convection in the Ozarks.  For this reason it looks
like the CWA will get a decent shot of DPVA on Thursday, along with
deep mid to upper level moisture. The low could be in position to
enhance low level moisture flux via onshore flow, but models also
hint at a possible secondary low developing along the sea breeze
front Thu afternoon, where CAM response is noted. Over our area, QPF
response is really pretty unremarkable given the number of factors
one might see at first glance. Perhaps this can be attributed to
winds not being very strong at any level, so there just may not be
enough frontogenetic or dynamic forcing to make much of a difference.
At any rate, with at least modest instability through a fairly deep
layer, the lower heights, and the return of seasonable moisture, at
least chance PoP will be included in all zones. PWATs should top out
near 2 inches, and with slow storm motion localized excessive
rainfall will be a concern. Chances linger into Thu night across the
SE half of the area, where either the sea breeze convection could
continue, or where the inland low/shortwave would still be providing
lift.

The front loses steam and appears likely to stall across TN/NC
Thursday night, with the sfc high pushing off the Northeast coast by
Friday afternoon. At 500 mb only a weakness remains of the trough,
with heights beginning to rise again by evening. What remains of the
front will be reactivated ahead of the next low moving into the Great
Lakes. Southerly or southeasterly flow should continue and dewpoints
will trend higher.  Drying will occur above 700 mb but this air would
appear too high to reach by diurnal mixing, so only a very minor
diurnal dip in dewpoints is expected. Flow remains weak through the
column, so overall we get back into a pattern like we saw early in
the week, with some instability but not much to promote initiation
aside from the southerly flow into the mountains and perhaps little
to sustain deep updrafts. Somewhat lower PoPs will be advertised. If
storms do kick off, owing to the drier air aloft we`ll trade some of
the heavy rain concern for the possibility of wet microbursts, if we
can eke out enough instability. Max temps will be fairly similar to
Thursday, remaining several degrees above normal, but dewpoints are
expected to trend a little higher, so heat concerns would appear to
increase. Low-level flow will amplify Friday night as pressure
gradient strengthens around the Great Lakes system. Most models show
an uptick in QPF overnight, presumably as this initiates elevated
convection.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 230 AM Wed: Cyclone will continue to track just north of the
US-Canada border, carrying another front thru the Ohio Valley and
into the Southeast late in the weekend. Dynamic forcing within the
surrounding trough looks to remain well north of the CWA. Prefrontal
convergence however should promote convective development across the
southern Appalachian region on Saturday, and marked height falls will
occur Sunday. Showers/storms appear likely over most of the area that
day. Although cloud cover should keep temps in check, moisture
pooling will result in soupy dewpoints and heat index probably
peaking for the period, in the low 100s across much of the Piedmont.
PWATs will be even more anomalously high compared to the Thursday
front, likely more than 2 SD above climo, with especially weak flow
through the column, and thus excessive rainfall and localized flash
flooding are possible (especially where soils remain wet from precip
late this week).  There remains some timing variation among the major
model solutions, but generally it appears the front will pass Sunday
night allowing continental high pressure to work into the area from
the NW. Deep drying will occur in time for temps to return to about
normal Monday along with lower dewpoints mixing out to the lower 60s
or upper 50s in most areas.  PoPs that day fall to the 20-40% range,
but focused mainly across the southern half of the area. Temps remain
near normal Tuesday although the sfc high by then will center over
the Mid-Atlantic coast and southerly moisture flux will begin again,
with a deep ridge or anticyclone forming over the lower MS Valley for
midweek. Precip chances will be a little below climo Tuesday.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
At KCLT and elsewhere: All terminals start off and should remain VFR
through the entire TAF period. High pressure continues to dominate
the region today. As a cold front approaches from the west, a few
areas in the mountains could see an isolated -RA or TS. Confidence
is low with less than a 25% chance at KAVL, which is why there is
currently no mention of convection or rain in the TAF. Overnight,
the cold front is expected to reach the mountains around 09-11z. The
front will weaken as it crosses the area through the day on
Thursday, but expect a wind shift. KCLT should see winds turn more
NE around 15z and return to SE near the 22-00z range Thursday
evening. Again, the front is not expected to be strong, keeping
overall wind speeds and any gusts low end. Though gusts are low-end,
cannot rule a g15 at any terminal. With the frontal passage, there
is an uptick in shower and TS possibilities Thursday afternoon.
Confidence still remains low, but is high enough to warrant a PROB30
for KCLT at this time. Will continue monitoring at future TAF
issuances.

Outlook: A cold front stalls south of the area on Friday, keeping
SHRA/TSRA chances around the region. Another cold front will impact
terminals this weekend along with an unsettled pattern into next
week.

&&

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

&&

$$

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