-- Discussion containing changed information from previous version are highlighted. --
494
FXUS62 KGSP 212123
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
523 PM EDT Fri Jun 21 2024

.SYNOPSIS...
A humid and subtropical airmass will return to the area this weekend
and remain into early next week, resulting in more typical
summertime shower and thunderstorm activity, as heat builds over the
region.

&&

.NEAR TERM /THROUGH SATURDAY/...
-- Changed Discussion --
As of 519 PM Friday...no major changes to the afternoon/evening
forecast.  Synoptic setup remains unchanged with deep upper
anticyclone centered over the Mississippi Valley and extending
well into the Mid-Atlantic.  Apart from some scattered mountain
stratocu, it`s clear across the board.

Over the next 24 hours, the center of the upper anticyclone will
shift slowly off to the SW, but will remain close enough to keep
a light NW to N flow across the region at mid/upper levels. This
becomes important when considering the fate of the weak system of
interest offshore of north FL. Given the weak flow over the western
Carolinas, it appears unlikely this system would have much of an
effect on us, other than to send a wave of low level moisture up
from the southeast by Saturday afternoon. That might be the most
noticeable thing in the weather...an increase in humidity. The NAM
would suggest dewpoints high enough to overcome the cap, but the GFS
remains more subdued outside the mtns because the cap remains strong
enough. Expect a few showers to develop over the higher terrain as
indicated in some of the CAMs, which will be carried over from the
previous forecast. East of the mtns remains too uncertain. High
temps will be about three degrees warmer than Friday, but even
with the increase in dewpoint, the apparent temp should stay well
short of Advisory criteria. Seasonally warm, nonetheless.
-- End Changed Discussion --

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
As of 145 PM EDT Friday: The upper ridge will retrograde somewhat as
we move into the short term Sunday, with the surface high well
offshore. Southeast flow around the surface high will continue to
bring WAA to the region, allowing temperatures to climb each day.
Afternoon highs are expected to be a good 5-8 degrees above seasonal
normals, climbing into the mid 90s across the Piedmont (slightly
warmer Tuesday than Monday), with heat indices touching just above
the 100 degree mark with the current forecast in southern zones as
well as the I-77 corridor both afternoons. Through the period, upper
trough will pass through the area, pushing offshore by the end of
the period, which will bring a return of diurnal convection to the
area.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 215 PM EDT Friday: The aforementioned upper trough will
continue to push offshore as we move into the extended to be
replaced by a secondary shortwave by midweek as upper ridging over
the Desert Southwest dominates. This will allow a more substantial
cold front to drop out of Canada and through the OH Valley towards
the Southern Appalachians by the end of the period. However, before
we can get there, we have to get through still very warm days on
Tuesday and Wednesday, with highs currently progged in the upper 90s
across portions of the Piedmont, and low to mid 90s in some mountain
valleys. Post-frontal dewpoints Tuesday drop off just a tad with dry
downslope flow so heat indices with the current forecast are not
quite as oppressive, but moisture return on Wednesday may lead to
increased dewpoints and higher heat indices, so later forecasts will
refine this. Minimal diurnal convective activity in the mountains
Tuesday but increasing activity as the front approaches Wednesday,
with enhanced pops (likelies in the mountains) by the end of the
period. For now, the approaching front knocks us down to just above
normal temps for Thursday but global guidance in disagreement on how
quickly the front pushes through.

&&

.AVIATION /22Z FRIDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: High pressure at the sfc and aloft
should continue to keep things quiet and suppressed through the
period. For the remainder of the afternoon, enough moisture is
present to allow for stratocu to develop underneath the persistent
subsidence inversion, so all terminals will be in-and-out of a VFR
sct/bkn cloud deck around 050-060. The low clouds should dissipate
with the loss of heating this evening, so clear overnight with
light/variable winds. Some of the guidance would have a low cloud
deck moving northwestward from the coast, perhaps impacting the
terminals outside the mtns, but for now the chance is not great
enough to include. There remains the possibility of low cloud/fog
restrictions in the mtn valleys as well, but again the confidence
is too low. For Saturday, low clouds are more likely to develop
earlier in the day as low level moisture should be greater on
a developing light SE flow. There might be a few showers in the
afternoon as the cap could be breached, but that remains beyond
the scope of this forecast.

Outlook: Isolated diurnal convection will be possible over the
mtns on Saturday afternoon, with a return to more sct convection
expected across the region Sunday and Monday.  Slight drying may
follow for Tuesday.

&&

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

&&

$$

SYNOPSIS...TDP
NEAR TERM...MPR/PM
SHORT TERM...TDP
LONG TERM...TDP
AVIATION...PM