234
FXUS62 KGSP 221439
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1039 AM EDT Tue Apr 22 2025

.SYNOPSIS...
A stationary front will remain across our area for a few days,
providing a focus for mainly scattered afternoon and evening showers
and thunderstorms. This pattern will repeat itself each afternoon
through much of the week as conditions remain warm and become
increasingly humid.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1035 AM EDT Tuesday: Showers and an occasional storm remain
over the area ahead of the weak frontal boundary sliding across the
area. The clouds across most of the area are slowing heating and
keeping instability from quickly ramping up. Still expect weak
instability and moderate shear for the afternoon as the atmos
eventually heats up. Expect storms, a few possibly severe, to move
across the area ahead of the slowly moving front. No changes to high
temps at this time.

Otherwise, a weak frontal boundary currently draped across the
southern Appalachians will ooze southeast across the forecast area
throughout the day. One area of showers and isolated TS lifting
northeast along the frontal zone will impact mainly the TN border
counties of NC early this morning. Meanwhile, additional showers and
thunderstorms continue to blossom across northern AL and northeast
GA in association with a weak short wave trough rippling through SW
flow aloft. This short wave and the frontal boundary (weak as it is)
will provide a focus for continued convective development throughout
the day, especially this afternoon...when ample moisture combined
with sufficient insolation is expected to allow for modest
destabilization to the tune of around 1000 J/kg of surface-based
CAPE (give or take) across much of the Piedmont. The highest PoPs
(generally 60-70%) will be reserved for the mountains, but chances
across much of the lower elevations are in the 50-60% range. As the
mid-level height gradient increases downstream of the short wave
this afternoon...deep layer shear is expected to increase to 30-40
kts. This may be just enough to allow for a severe storm or two to
develop across the Piedmont. With low-level shear remaining
weak...the main threat will be from damaging downburst winds and
perhaps marginally large hail with any cells exhibiting mid-level
rotation. Max temps will be notably less warm than in previous
days...but still should be around 5 degrees above climo across all
but the mountains and NC foothills, where maxes should be closer to
normal.

Coverage and intensity of convection will diminish this evening,
especially with the short wave trough shifting east of the forecast
area. Nevertheless, some degree of shower coverage is likely to
continue through the overnight. Rainfall totals through 12Z Wed
should be rather modest...basin averages generally .25-.50" across
the mtns and 0.1-0.25" elsewhere. Locally higher amounts will
nevertheless occur in areas directly impacted by thunderstorms.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 135 AM EDT Tuesday: Quasi-stationary frontal boundary
draped across the CFWA will set the stage for an ongoing unsettled
pattern through the short-term. Ample moisture transport (PWAT:
1.25"-1.50") with west-southwesterly flow to go along with diurnal
destabilization in the vicinity of the frontal boundary will lead to
a growing coverage of scattered showers and a few thunderstorms on
Wednesday. With the presence of the quasi-stationary front, a few
training showers and storms may exist, providing more beneficial
rainfall to locations that receive multiple rounds of locally heavy
rainfall. Modest destabilization and weakly sheared environment
suggest a pulse type of setup, with a very low severe threat.
Coverage should wane during the nighttime period, but lingering
showers and few thunderstorms will continue overnight Wednesday with
30%-50% PoPs due to the presence of the boundary. Increased cloud
cover and rainfall chances will lead to temperatures being up to 5
degrees above normal for afternoon highs and ~10 degrees above
normal for overnight lows.

Frontal boundary remains quasi-stationary Thursday with another
round of focused diurnal showers and thunderstorms in the
vicinity of the front. Similar thermodynamics to Wednesday and
not much change overall are expected to the synoptic setting
and sensible weather. The one caveat is a weak shortwave that
shifts over the area late Thursday, which could keep shower and
thunderstorm coverage more elevated past the typical peak diurnal
coverage. Otherwise, temperatures for afternoon highs on Thursday
will be near-normal as a transient surface high shifts across the
northeastern CONUS and eventually offshore the Northeast Coast by
Thursday night, allowing the potential for a weak in-situ wedge
to develop mainly over portions of the Piedmont and foothills as
surface northeast winds fights the battle against the stalled
boundary. Extensive cloud cover and increased rainfall chances
overnight Thursday will keep overnight lows ~10 degrees above
normal.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 300 AM EDT Tuesday: Overall regime will be the same on Friday
compared to the short-term forecast period with diurnal showers and
thunderstorms. Model guidance continue to send a potent shortwave
across the Great Lakes and Northeast Friday into Saturday with a
reinforcing cold front. The quasi-stationary boundary will gradually
undergo warm frontal activation and lift north of the area Friday
in response, placing the CFWA into an open warm sector ahead of the
front. The cold front is expected to push across the area Saturday
and should uptick coverage in convection in response. Guidance
indicate that the front completes an actual fropa by Sunday as a
surface high builds in over the Northeast and Mid-Atlantic. Expect
drier weather by Sunday and into the early part of next week
as a mid-level ridge moves over the southeastern CONUS. NBM and
probabilistic guidance maintain a diurnal slight chance to chance
PoP over the mountains through the end of the period, but most
locations are expected to be much drier. Temperatures will return
back to 5-10 degrees above normal during the medium range.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: A weak front currently draped across the
southern Appalachians will sag southeast across the Terminal
Forecast Area today...eventually stalling. A couple of waves of
showers and scattered thunderstorms associated with an upper air
disturbance will move across the area today...one early this morning
that will pass near KAVL, but will otherwise not effect the
terminals...and another that will move across the area from late
morning through the afternoon. VCSH and Prob30s for TSRA are used
liberally at most sites during this time frame, with a tempo for
TSRA limited to KCLT for the time bring...as this is where the
highest instability is forecast this afternoon.

Clouds will otherwise continue to slowly increase and lower through
the morning, but cigs (and visby) are expected to remain
predominately VFR through at least this evening, with any visby/cig
restrictions limited to the passage of a shower or a storm.
Intensity and coverage of convection are expected to diminish this
evening, but at least isolated showers should linger through the
overnight. Winds are expected to be light through the period,
starting out S/SW, but steadily coming around to N/NW late today as
the front sags south. Visby and cig restrictions become
possible...if not likely late tonight/early Wed, with the extent of
said restrictions depending largely upon how much...if any rain
falls at the terminals today. For now...visby is primarily
advertised in the 4-6SM range, while use of FEW/SCT MVFR layers is
used to indicate the low cig potential.

Outlook: Mainly diurnal showers/thunder and associated restrictions
will continue each day through the end of the week. Patchy fog
and/or low stratus may develop overnight into sunrise each morning,
especially where heavier downpours occurred the previous afternoon/
evening.

&&

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

&&

$$

SYNOPSIS...CAC
NEAR TERM...JDL/RWH
SHORT TERM...CAC
LONG TERM...CAC
AVIATION...JDL