702
FXUS62 KGSP 250543
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
143 AM EDT Tue Jun 25 2024

.SYNOPSIS...
Dry and less humid conditions continue today before the heat and
humidity returns Wednesday ahead of an approaching cold front. This
front will bring showers and thunderstorm chances back to the area
late Wednesday into Thursday. Hot and humid conditions will persist
into the weekend with a chance of showers and thunderstorms each
afternoon. Another cold front approaches the area late this weekend
keeping unsettled weather around.

&&

.NEAR TERM /THROUGH TODAY/...
As of 100 AM EDT Tuesday...No major changes were needed as the
forecast remains on track with dry and clear conditions in place.
Otherwise, in light of today`s dewpoint crashing, opted to make some
tweaks to tomorrow`s dewpoints, as GFS and NAM forecast profiles
depict even drier air aloft.  Mixing potential is still in question
given a steeper subsidence inversion than today`s likely to be in
place across the area; still, it seemed reasonable to bring values
down a little, to at least match the latest hi-res guidance blend.

A small-scale sfc high currently located over WV will migrate
southeast and off the Carolina coastline thru the period and keep
winds unfavorable for sfc-layered moisture transport, thus a morning
fog threat will be nil especially with the pressure gradient
remaining a little tight allowing for weak sfc mixing. On Tuesday,
expect the upper ridge to remain dominant and large scale subsidence
negating any precip/thunder. Lows this morning will remain a couple
degrees above normal, while highs once again rise above normal by 5-
7 degrees due to great insolation.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
As of 230 PM Monday...The hottest temperatures of the forecast
are expected for Wednesday ahead of an approaching cold front.
Highs in the mid- to upper 90s east of the mountains are expected
Wednesday afternoon, with highs in the lower 90s in the mainstem
mountain valleys.  These highs will still be about 3-5 degrees
below long-standing records.  Dewpoints Wednesday afternoon are
expected to reach the mid- to upper-60s which would be enough
to push heat indices to the 100-102 range in typical locations
including Charlotte and the Upper Savannah River Valley, but nothing
unusual for this time of year.  Despite deep-layer mixing and high
cloud bases; SBCAPE values of 1500-2000 J/kg are expected with
steep low-level lapse rates; therefore, the approaching shortwave
energy and the mountain terrain should provide enough forcing for
scattered shower and thunderstorm development, especially across
the mountains.  Bulk shear values of less than 20 kts precludes
any significant concern for severe weather; however, ample dry-air
aloft/downdraft CAPE suggests a strong downburst or two cannot be
ruled out.  Overall, given underwhelming moisture content through
the column, we are not expecting notable precip outside of isolated
locations with this activity.

The latest guidance stalls the front near or just to the south
of our forecast area for Thursday.  Compared to Wednesday, the
resultant airmass is actually a bit more moist through about 500mb,
especially in the mountains.  Lapse-rates aren`t as steep through
the mid-levels as on Wednesday, but the LCLs/cloud bases are
expected to be a bit lower as well.  Forecast soundings suggest
unimpressive SBCAPE values below 1000 J/kg, but the proximity of
the decaying frontal boundary should be enough for another round of
scattered showers and general thunderstorms, with numerous showers
and thunderstorms possible over the mountains thanks to typical
terrain-induced forcing/enhancement.  Bulk shear values remain
below 20kts; therefore, we still lack a notable severe storm threat.
National Blend guidance is a bit more aggressive with PoPs Thursday
afternoon than preferred given the profile and pattern, but this
will be another high PoP/low QPF scenario with little appreciable
rainfall expected outside of isolated locations.  Expect little
moderation behind the front east of the mountains with highs 2-4
degrees "cooler" than Wednesday, but still 2-4 degrees above normal.
The influence of the front will be a bit more discernible in the
mountain valleys, with highs 5-7 degrees cooler than Wednesday,
though these highs will still be slightly above normal.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 230 PM Monday...The extended period will feature a resurgence
of the heat ridge over the Lower Mississippi River Valley, keeping
our area on the southern fringe of the active westerly flow across
the northern half of the ConUS.  This upper-level pattern suggests
that we should be able to maintain diurnally driven isolated to
scattered shower and thunderstorms Friday and Saturday with the
best coverage in the climatologically favored mountain zones.
Once again, there is not enough forcing or moisture to suggest any
notable relief from ongoing dry conditions.  High temperatures are
expected to remain several degrees above normal through Sunday,
with low-level flow gradually becoming more conducive for moisture
advection from the Atlantic and eastern Gulf.  Therefore, expect
increasingly humid conditions heading into the weekend, as the next
cold front approaches the area later Saturday into Sunday.  It may
become increasingly difficult to mix out the low-level moisture
and current guidance suggests afternoon dewpoints into the lower
70s are likely Saturday and Sunday.  If this materializes, we can
expect more widespread heat indices in the 100-104 range across
the Piedmont, especially on Sunday when our high temperatures peak
in the 94-97 range.

The aforementioned moisture flux into the region through Sunday may
put us in a better position for more notable convective coverage
and rainfall along and ahead of the cold front, which is currently
expected to enter the area later Sunday.  While it is much too early
to get our hopes up, the favorable return flow may allow PWs to
approach 1.75-2 inches with ample instability.  Bulk shear values
look anemic at this time, so the primary focus here is improved
coverage and better opportunities for some much-needed rainfall.
At this time, the front is expected to clear the area by Monday
morning.  If this occurs, we can expect max temperatures several
degrees lower than Sunday, though we may see little relief from
the humidity.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: VFR and dry through the 06Z TAF period
thanks to sfc high pressure. Wind speeds will range from 3-7 kts
through daybreak, potentially increasing to 5-9 kts east of the
mountains for a short period after daybreak. With wind speeds
remaining elevated, fog formation is not expected at this time.
Brief low-end wind gusts cannot be entirely ruled out east of the
mountains from 11Z-13Z as the pressure gradient tightens slightly.
However, confidence remains too low add any mention of gusts for
now. Wind direction will remain N`ly through daybreak before
gradually turning more NE east of the mtns through the morning
hours. Winds become more light and VRB this afternoon into tonight
across the terminals. A few cumulus should develop this afternoon
before dissipating around sunset.

Outlook: Widely scattered SHRA/TSRA returns Wednesday afternoon and
evening as a cold front approaches out of the west. The cold front
will track over the terminals Wednesday night into Thursday before
stalling south of the area on Friday, keeping SHRA/TSRA chances
around.

&&

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

&&

$$

SYNOPSIS...AR
NEAR TERM...AR/MPR/SBK
SHORT TERM...JMP
LONG TERM...JMP
AVIATION...AR