-- Discussion containing changed information from previous version are highlighted. --
999
FXUS62 KGSP 270733
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
333 AM EDT Sat Jul 27 2024

.SYNOPSIS...
Drier air will push south into the area today, making for somewhat
milder temps and more comfortable humidity, while also keeping
shower and thunderstorm activity confined to the mountains and
upper Savannah River Valley. Shower and thunderstorm chances
increase again across the area early next week as another moist
frontal system approaches from the west.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 310 AM: Low-level flow has turned northeasterly over most of
the area, as negatively tilted upper trough drifts southeast over
the Mid-Atlantic coast, and sfc high pressure fills in beneath the
trailing sharp ridge. That said, not expecting appreciable surface
drying until after daybreak. Trough axis is aligned near sfc cold
front leaving abundant moisture and pockets of weak forcing. Showers
have pretty much fizzled over the mountains and Upstate but can`t
completely rule out something developing anew. Low clouds are slowly
expanding across the NC Piedmont and are expected to reach most
of the NC foothills and northeastern Upstate by dawn, particularly
as higher cloud decks thin or advect out allowing better radiation.

The trough axis will exit today and appreciably drier air will
arrive above 700 mb; by midday the low clouds should dissipate
and some of the sfc moisture will mix out. Although a subsidence
inversion looks unlikely to develop this far south, the dry air
should kill any deep convective updrafts in the eastern CWA and
skies should remain mostly sunny. Further west, low to midlevel
moisture will be a tad better and mechanical lift and/or ridgetop
convergence will give a bit of a boost. PoPs are retained at
likely/numerous in a portion of the SW mountains and Escarpment area
but these taper off to only a isolated to widely scattered mention
NE of the French Broad Valley. Another day of warm but slightly
below-normal aftn temps, but dewpoints should be able to mix out
a few degrees into the mid 60s, making it a bit more bearable
than we`ve seen lately. A couple spots in the NC Piedmont may tap
into even drier air and mix out to around 60. PWATs fall to around
normal in the area with the best precip chance today, mitigating
flash flood threat to some extent. However, deep cloud layer flow
will be opposite the low-level flow likely to initiate any showers,
so very slow movement or terrain anchoring still will be possible.

On the other side of the upper ridge, a weak cutoff low will drift
north across the Ozarks and reach the upper MS Valley tonight. Sfc
high will move to the East Coast and the eastern trough will also
cut off, leaving the pattern briefly in an omega configuration
by Sunday morning. This looks likely to veer sfc winds to SE,
helping the low levels to moisten again, and some sources thus bank
stratus or stratocu against the Escarpment tonight. Can`t rule
out an isolated shower in our SW zones this evening as well. The
eastern two thirds of the CWA should see a partly cloudy night
and temps will cool a category or so compared to this morning.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
-- Changed Discussion --
As of 200 AM EDT Saturday: Narrow upper ridge axis will set up
shop over the CFWA by the start of the forecast period as a weak
surface high slips south into the Mid-Atlantic and Carolinas by
Sunday afternoon. In this case, limited diurnal convection will be
in store for Sunday as most of the activity will remain confined to
the mountains/foothills as a wedge of drier air filters into the
northeast quadrant of the CFWA. Deepening upper low over the western
Atlantic will slowly lift north as it becomes engulfed by the main
branch of the subtropical jet by the end of the forecast period. On
the other hand, a digging shortwave trough over the Midwest and
Upper Great Lakes region will breakdown the upper ridge axis as a
plume of deep layer south-southwesterly flow filters in overnight
Sunday. With associated DPVA residing within the mean flow and a
good moisture fetch, expect enough forcing for ascent to place
lingering convection across the western half of the CFWA Sunday
night and kept PoPs in the forecast as a result. PWAT values quickly
rise to 1.50"-2.00+" by Monday as the synoptic pattern introduces
height falls and baggy upper troughiness settles over the region to
go along with a stronger transport out of the GOM. Factor in modest
destabilization and weak deep layer shear, expect for the excessive
rainfall threat to return, especially in the mountains where daily
convective chances will remain elevated through the forecast period.
Severe threat will be limited as profiles indicate more of a flood
threat with skinny CAPE, warm cloud layer above 12,000`, and weak
MBE velocity vectors. Expect elevated PoPs to remain in the forecast
Monday night, but the activity will have a diurnal emphasis as far
as coverage and potential threats. Temperatures will remain slightly
below-normal for afternoon highs and slightly above-normal for
overnight lows.
-- End Changed Discussion --

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
-- Changed Discussion --
As of 300 AM EDT Saturday: An active pattern will be in store
through at least midweek next week as the baggy upper troughiness
lingers across the Eastern Seaboard, providing continuous height
falls and synoptically enhanced forcing residing within the mean
flow. This setup will overlay with typical summertime environmental
parameters and thus, PoPs will remain elevated with convection
expected during peak heating and possibly outside of the normal
diurnal cycle. The excessive rainfall threat will uptick as a result
as high PWAT values and weak deep layer shear will continue within
this regime. Model guidance slowly, but surely push the trough
axis across the area midweek and introduces mid- to upper-level
northwesterly flow as the axis slips east of the area. Heights
will begin to rebound in response and bring typical mid-summer
convection and temperatures by Wednesday and beyond. One thing
to note, the synoptic setup per model guidance would provide the
potential for decaying/ongoing MCSs to dive into the area from the
northwest as this activity rounds the northern peripheral of an
upper anticyclone over the south-central CONUS by the latter half
of the medium range. Otherwise, the Dog Days of Summer will likely
make a return for the end of the forecast period as temperatures
uptick to above-normal by D6/D7, with heat indices reaching into
the upper 90s and lower 100s by next Thursday and Friday. If
the pattern becomes favorable for potential MCSs late into the
extended period, expect for a few temperature forecasts to bust
due to unexpected cloud cover and precip chances.
-- End Changed Discussion --

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Backdoor front sagging into the area from the
N will promote some degree of drying for much of the terminal area
thru today. Multiple cloud decks are present with continuing band of
moisture overlaid by weak train of upper disturbances. With guidance
handling this weakly forced regime fairly poorly, confidence is not
especially high, and sites where IFR or low MVFR cigs are already
floating nearby have been given a TEMPO to start the period. Winds
are already northerly and with slight dewpt depressions vsby
issues this morning look likely to be limited to those areas that
saw heavy rain or perhaps near rivers. A few SHRA also are likely
to linger this morning but become increasingly isolated. Easterly
flow above the PBL and frontal convergence are expected to bring
low stratus to the NC sites around daybreak. Low LCLs and CCLs
suggest a "sunrise surprise" also is possible after daybreak where
breaks are present in the higher decks. Thus restrictions appear
in most TAFs through late morning except at KAND. Drying and weak
subsidence should limit mentionable convective coverage this aftn
to the mountains and Savannah Valley. PROB30 TSRA at KAVL and
VCSH at the SC sites. Winds will veer to SE by evening but diurnal
convection should wane. The SE flow may develop stratus near the
Blue Ridge Escarpment tonight if not also the SC sites or KHKY,
but not confident enough to mention except at KAVL.

Outlook: Drier air will remain over the central and eastern
Carolinas Sunday leaving scattered SHRA/TSRA possible only over
the mountains. Moisture and unsettled weather return at times Mon
to Wed with shortwave and moisture plume crossing the area.

&&

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

&&

$$

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