361
FXUS62 KGSP 271104
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
Issued by National Weather Service Columbia SC
704 AM EDT Thu Jun 27 2024

.SYNOPSIS...
A cold front will track across the area today leading to producing
scattered showers and thunderstorms. Hot and increasingly humid and
unsettled conditions are expected Friday through Sunday. Another
cold front moves through the area Sunday night, ushering in a more
seasonable airmass for Monday and Tuesday before heat begins to
return to the area for Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Messages:

1) Less Hot and Humid Today as a Cold Front Stalls Over the Western
Carolinas

2) Showers Associated with the Front May Survive East of the
Mountains this Morning

3) There is Low Confidence on Additional Shower/Thunderstorm
Development this Afternoon/Early Evening

As of 630 AM EDT Thursday: Thick cloud cover and light rain
continues pushing east this morning. Went ahead and increased PoPs
in the NC mtns where it`s currently raining otherwise no other
changes were needed as the forecast remains on track. Upper
troughing will persist through the near term while a cold front
stalls over the western Carolinas and northeast Georgia through
tonight. PoPs will be tricky through the near term thanks to the
stalled front. Currently seeing showers in association with the
front tracking east across the NC mountains this morning. CAMs all
seem to agree that light rain showers will hold together east of the
mountains as activity progresses eastward through the morning hours.
Thus, have PoPs expanding westward through the morning. However,
capped them to 45% (outside of where it`s currently raining) for now
as confidence on whether the light rain can overcome the dry air and
reach the ground east of the mountains remains low. Lows this
morning will end up ~6-9 degrees above climo thanks to precip and
cloud cover.

The 06Z CAMs depict the light rain shield pushing out of the
forecast area (or falling apart) before another round of scattered
showers, and perhaps thunderstorms, develops across the NC mountains
early this afternoon. CAMs show activity gradually weakening as it
progresses south and east this afternoon into early this evening.
Confidence on whether this second wave of convection will have any
thunder, or will even develop, remains low as morning precip and
lingering afternoon cloud cover should limit destabilization. With
the 06Z HRRR and NAMNest now showing drier conditions (compared to
the 00Z runs) after the morning rain, confidence on PoPs through the
period remains low. Thus, capped PoPs this afternoon to chance (30%-
50%) for now. Luckily the front will lead to much cooler high temps
(near climo) and lower humidity this afternoon. Highs have trended
down a few degrees across the forecast area compared to the previous
forecast. Temps will only climb into the mid to upper 80s along and
north of I-85 (east of the mountains). Temps south of I-85 will
range from the upper 80s to lower 90s. The mountains will see highs
ranging from the mid 70s to lower 80s. Cloud cover should gradually
decrease from west to east this afternoon into this evening,
becoming scattered. Scattered showers (and perhaps isolated
thunderstorms) may linger through the early evening hours, mainly
across the southern half of the CWA. However, confidence on this
remains low due to the 06Z HRRR and NAMNest coming in drier. Thus,
capped PoPs to chance (less than 40%) through the early evening
hours. Lows tonight will end up ~5-7 degrees above climo thanks to
some lingering cloud cover.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
As of 245 AM Thu: Continental sfc high pressure will move
across the northeast CONUS on Friday, pushing offshore by
that evening. Little in the way of airmass change is expected;
weak easterly flow will occur up to 850 mb over the CWA, still
promoting some degree of Atlantic moisture flux and allowing a
hint of mechanical lift. Higher aloft flow will remain southerly,
but without much flow thru a deep layer of the column there won`t
be much else to kick off convection. A weak capping inversion may
result in lots of trapped cumulus, and partial cloud cover would
appear to help limit temps to around climo. Model CAPE values
are somewhat subdued. The CAMs at that range develop scattered
but largely unremarkable convection; dry air entrainment above
600 mb will restrict deep updrafts. We retain scattered/chance
PoPs for the whole area with the best chances near the Blue Ridge
Escarpment. Locally heavy rainfall will be possible and perhaps
a couple storms producing strong downburst winds, but these are
just seasonable threats. Dewpoints may not mix out below 70 in
many spots but with the climo temps heat index still doesn`t top
100 except in a few spots.

Friday night the low level winds come around to the south in advance
of the trough moving across the northern tier of the CONUS, and
elevated convection will remain possible so PoPs continue thru the
night. Upper level flow will be somewhat more cyclonic on Saturday;
front enters the middle MS Valley, but shortwave remains near the
northern Great Lakes. The main difference will be better moisture
flux on the south winds bringing dewpoints and CAPE higher, and
less subsidence or dry air aloft to mitigate updrafts. Coverage
should increase such that likely PoPs are forecast for the northwest
half of the CWA as well as the Savannah River Valley. Weak shear
persists, but more moisture means lower DCAPE so perhaps somewhat
less potential for storms to produce strong winds. PWATs rise above
2 inches so heavy rain is still more likely. Activity should have
an opportunity to wane diurnally Sat evening as winds veer and low
level lapse rates diminish, but convection ahead of the approaching
front in the Ohio Valley may make a run at the mountains overnight
so small PoPs linger into Sunday morning near the TN border. Weak
vort axis looks to cross the area Sunday as a remnant of that
activity. Low level convergence and stronger low level winds will
further help moisture flux and PWATs look to top out above 2 inches,
near the daily record values. However, this looks likely to occur
early in the day, and by peak heating downslope winds already are
expected to develop. SBCAPE still will be high for the season; the
actual sfc front still will be to the west, and so we will continue
to feature mostly likely PoPs for the area, with some strong to
severe wind gusts possible for storms that develop in the drier
air behind the moisture plume. Temps will rise back to the lower
90s assuming cloud cover invof the vort axis advects out in time,
and the downsloping develops. Heat index is likely to top 100 in
much of the Piedmont but still likely below advisory criteria.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
As of 315 AM Thu: Deep drying is likely behind the front Sunday
night, with continental sfc high and subsidence downstream of
developing south-central CONUS ridge. While the timing of the front
is pretty well agreed upon by guidance members, there are varying
depictions of how far the front pushes through the area before
stalling, and perhaps on how effective mixing is on the cool/dry
side of the front. Dewpoints Monday should be lower than Sunday but
with limited confidence we will only show a modest decrease in the
forecast. Temps fall back several degrees as well, below climo in
most of the NC zones and near climo to the south. Those ensemble
members which stall the front more quickly still develop some
instability in our south, so small PoPs are retained there. Sfc high
will migrate to the East Coast Tuesday, maintaining the relatively
mild and dry air another day but possibly allowing southerly flow
to develop atop it, so small PoPs remain over the SW half. Temps,
dewpoints and PoPs all tick upward Wednesday with the high likely
in position offshore and with return flow occurring ahead of the
next wave moving across the Midwest.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: A more active pattern is on tap for the 12Z
TAF period thanks to a cold front stalling over the western
Carolinas. VFR cloud cover continues to thicken from west to east
this morning and will continue increasing throughout the rest of the
morning. Cigs will gradually lower to low-end VFR levels through
early this afternoon. Cloud cover should gradually decrease from
west to east late this afternoon into this evening becoming FEW to
SCT with some low-end VFR cigs lingering in the mountains. Showers
continue across the NC mtns this morning along the cold front.
Activity is expected to weaken while progressing eastward through
the rest of the morning. Have TEMPOs at all terminals to account for
-SHRA this morning. Confidence on additional SHRA/TSRA development
this afternoon remains very low as lingering cloud cover and morning
rain should limit destabilization. Went with dry conditions this TAF
update for this afternoon and evening as the 06Z CAMs are now
showing drier conditions behind this morning`s rain so have dry
conditions persisting after this morning. Wind direction will be
N/NE`ly behind the front this morning east of the mountains. Winds
will remain NW at KAVL through this afternoon before becoming VRB
this evening. Winds east of the mtns will remain N/NE`ly through
early this afternoon before becoming VRB late this afternoon into
this evening. With the front stalling across the area this evening
into tonight low-level moisture will linger across the area. This
may allow patchy fog to develop, mainly at KAVL and KHKY. MVFR cigs
may develop at KHKY and IFR to low-end MVFR cigs may develop at KAVL
at the end of the 12Z TAF period as well. Winds should remain light
and VRB late tonight before picking up out of the NE/ENE east of the
mountains towards the end of the period. KAVL should see winds pick
up out of the SE towards the end of the period.

Outlook: The cold front will remain stalled south of the area on
Friday, keeping SHRA/TSRA chances around the region. Another cold
front will approach out of the west this weekend before pushing over
the terminals Sunday night. This will keep the unsettled weather
around through early next week.

&&

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

&&

$$

SYNOPSIS...AR/JMP
NEAR TERM...AR
SHORT TERM...Wimberley
LONG TERM...Wimberley
AVIATION...AR