773
FXUS62 KGSP 270746
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
346 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 later this Morning

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

As of 330 AM EDT Thursday: 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 northeastward across the western
NC mountains this morning. CAMs all seem to agree that light rain
showers will be able to 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. Thick cloud cover is also
noted across the western two-thirds of the CWA this morning and will
continue to thicken as it spreads east through the morning hours.
Lows this morning will end up ~7-9 degrees above climo thanks to
precip and cloud cover.

The 00Z CAMs depict the light rain shield pushing out of the
forecast area (or even just 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 even develop, remains low as morning
precip and lingering afternoon cloud cover should help limit
destabilization. With the incoming 06Z HRRR now showing mostly dry
conditions in place behind this morning`s rain shield, confidence on
PoPs through the period will be 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 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 /08Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: A more active pattern is on tap for the 06Z
TAF period thanks to a cold front tracking over the western
Carolinas this morning before stalling over the area into daybreak
Friday. VFR cloud cover continues to increase from west to east this
morning, with the thickest cloud cover noted across the western half
of the forecast area as of 06Z. Cloud cover will continue increasing
throughout the morning hours while cigs gradually lower to low-end
VFR levels. 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 have
developed ahead of a cold front along the NC/TN border. Activity is
expected to weaken while progressing eastward through the morning
hours. KAVL is the most likely terminal to see rain this morning so
have prevailing -SHRA from 08Z-15Z. Decided to go with a VCSH
mention elsewhere later this morning as activity may hold together
as it pushes east of the mountains. Confidence on the TSRA threat
this afternoon remains very low as lingering cloud cover and -SHRA
may limit destabilization somewhat. Thus, only have a PROB30 for
TSRA at KAVL and KAND for now as these terminals would have the best
chance to see scattered TSRA this afternoon. Went with dry
conditions elsewhere as activity looks to remain too isolated for
the rest of the terminals to maintain PROB30s at this time. Wind
direction will remain S`ly east of the mtns behind the front,
gradually turning N/NE`ly behind the front through daybreak. Winds
will remain NW at KAVL through this morning becoming VRB this
afternoon. 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, isolated to scattered convection may linger. However,
confidence is too low to mention with this being towards the end of
the 06Z TAF period.

Outlook: Patchy fog and low cigs may develop Thursday night into
Friday morning thanks to lingering low-level moisture. 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