295
FXUS62 KGSP 261752
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
152 PM EDT Fri Sep 26 2025

.SYNOPSIS...
A cold front will slowly cross the area tonight before stalling
along the Carolina Coast this weekend, keeping unsettled weather
around. A tropical system may impact the area early next week but
this remains uncertain at this time. Temperatures will be near
normal through the weekend, then drop to slightly below normal.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 137 PM EDT Friday: Scattered convection is expected to develop
this afternoon and evening as 1000-2000 J/kg of SBCAPE has develop
to go along with high PWAT values for this time of year (1.50"-
2.00") and 30-40 kts of deep layer shear. Some organized convection
leading to heavy downpours, gusty winds, and cloud-to-ground
lightning will be the primary threat. Can`t rule out a rogue strong
to severe wind gust, but the threat is low at this time.

Positively-tilted trough situated from the Lower MS Valley to the OH
Valley will only slowly propagate eastward, while the attendant
frontal boundary remains quasi-stationary across the area, mainly
east of the mountains throughout the forecast period. Deep layer
south-southwesterly flow will help to transport a deep conveyor belt
of moisture across the Southeast as a result, with the opening
entrainment from the Gulf. Model guidance try to cutoff the trough
and have it stall over the southeastern CONUS through the period,
but has a hard time fully completing this transition. However, PWAT
values between 1.50"-2.00" in place outside of the mountains, which
indicates a very saturated atmospheric column via soundings with a
warm deep cloud layer and skinny CAPE. In this case, any shower or
thunderstorm that develops will likely produce heavy rainfall this
afternoon and evening. 300-850mb mean wind show ~30 kts from the
southwest indicating that storm motions should be very progressive,
but some training is possible along the aforementioned boundary.
There is also some potential for anchoring and/or upslope
development along the Blue Ridge Escarpment that could cause sparse
hydro concerns as well. This would lead to localized instances of
flash flooding, but confidence isn`t high on exact locations due to
the scattered nature of the convection. Afternoon highs return to
near-normal values thanks to extensive cloud cover and precipitation.

Heavy rainfall from showers and thunderstorms should continue
overnight as upper divergence and mid-level DPVA continue to support
additional convection development, while the boundary remains draped
over the CWFA. 12Z HREF 3-hour PMMs highlight the Charlotte area
and northwest Piedmont as the best candidates for heavy rainfall
overnight tonight, but can`t be ruled out elsewhere based on the
exact position of the boundary, where low-level convergence will
be greatest. With 1.00"-3.00+" in locations that received the most
rainfall, localized flash flooding is possible, especially in urban
areas and locations in the vicinity of the stalled boundary. The
axis of heavy rainfall gradually shifts east of the I-77 corridor
after mid-morning Saturday, with some lingering light precip through
the rest of the morning hours. Overnight lows will run a category
or two above-normal with continued cloudiness and precip.

CAMs have consistently developed diurnal convection in the mountains
along the southwest facing slopes and ridgetops Saturday afternoon,
while a lull in precipitation is in store east of the mountains. The
trough axis begins to move across the area during this time frame
as drier air tries to punch into the mid-levels, while enough
available moisture, orographic enhancement, and instability
(500-1000 J/kg of SBCAPE) will help to develop convection. CAMs
try to have this activity break containment east of the mountains,
but will likely need to be outflow driven for this to occur,
which some of the guidance indicates. Any severe weather threat is
low, but nonzero as downbursts are possible in the strongest storms
that form. Low-end hydro concerns can`t be ruled out either,
especially locations that receive heavy rainfall amounts this
afternoon/evening and/or overnight tonight. Afternoon highs on
Saturday will remain near-normal with extensive cloud cover and
elevated precip chances.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
As of 130 PM Friday...Models are in reasonable agreement on an upper
trough axis over the Southern Appalachians to start the short term
at 00z Sunday. But they quickly diverge on how strong of a closed
low forms from this, as a piece of energy breaks off from the
trough Sunday into Monday. This weak upper low will likely linger
thru at least 00z Tuesday. Meanwhile, high pressure will build
over the Great Lakes. The biggest source of uncertainty in the
forecast is the evolution of a tropical disturbance (Invest 94L)
that is currently east of Cuba, but is expected to drift NW into
the Bahamas. The latest guidance is still coming in at the time
of this writing, but the 12z GFS is once again strengthening the
low fairly quickly and having it merge with the aforementioned
upper low. This would sling the tropical system NW into the
Carolinas. The GFS has consistently been the most bullish of the
deterministic models on this, but does have the support of some
of the hurricane models. But other guidance, including the 12z
Canadian and numerous ensemble members either stall the system
or push it east before making landfall. Even if the GFS were to
verify, any impacts to our forecast area wouldn`t start before
the end of the short term. If anything, conditions should be
relatively quiet thru Monday, as drier NELY flow increases around
the building high to our north and whatever tropical system forms
to our south. There may be enough diurnal instability for scattered
showers both Sunday and Monday. Highs will be near normal Sunday,
but a few degrees below normal Monday, as clouds increase ahead
of the tropical system. Lows will be a few degrees above normal.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 1:45 PM EDT Friday...There is still a lot of uncertainty on
what Invest 94L (which will likely become Imelda at some point)
will do. As mentioned in the Short Term section, the GFS is close to
a worse case scenario for our area, with a strong system (possibly
a hurricane) making landfall along the SC coast, but then drifting
west and stalling somewhere invof the Central Savannah River Valley.
This low would then be blocked by a strong ridge over the Great
Lakes to the northern Mid-Atlantic, which could keep our area in an
easterly atmospheric river setup well into the week. Storm total
precip could really pile up in this situation. With that said,
most of the guidance keeps the bulk of the heaviest precip with
this system to our south and east, with varying time periods of when
that heaviest rain would occur. This is due to the possibility that
the low gets blocked by the upper ridge before making landfall,
then meanders around Carolinas like the 00z ECMWF depicts. This
scenario could still result in areas of heavy rainfall during
the middle of next week, but not as bad the the GFS. Then, the
12z Canadian has continued its trend of keeping the low off the
Carolina Coast, with the sfc high pres axis further south. This
would bring just a brush of moisture along the northwest side of
the low`s circulation, then keep our area mostly dry with just
breezy NE winds for the rest of the week. All of this to say, the
fcst confidence is very low right now. Going with the latest NBM
results in high-end chc to low-end likely PoPs late Monday into
Tuesday, but then trending toward slight chc to dry condition
Wednesday and beyond. Temps should trend toward below normal,
as guidance at least agrees on a fairly strong sfc high to our
north that may cause cold-air damming thru the medium range.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Cigs have improved for this afternoon
with mixing and scattering in the low-levels, but low-end
VFR still in place, with isolated MVFR. A round of scattered
showers and thunderstorms are expected this afternoon, so
placed a TEMPO with the best timing for storms and associated
restrictions. Guidance continues to crash cigs and vsbys once again
overnight tonight through mid-morning Saturday with IFR/LIFR/VLIFR
restrictions. Prevailing shower restrictions are in place as well
with high resolution guidance in good agreement with showers and
isolated thunderstorms sticking around through the overnight hours,
especially across the Piedmont terminals. Winds will generally run
southwest to west-southwest. However, with the presence of a stalled
frontal boundary, there will be variability at times. Timing is a
little later on Saturday morning in regards to lifting/scattering
cigs and vsbys with precipitation in the area. Another round of
showers and thunderstorms are expected Saturday afternoon/evening,
but should stay mostly confined to the mountains, but can`t rule out
some of the activity slipping east in the Piedmont late afternoon
and evening. This will be reflected in the 00Z TAF update.

Outlook: Shower and thunderstorm chances, as well as associated
restrictions, continue for all terminals into the weekend thanks to
a stalled cold front along the Carolina coast. Fog and low stratus
are possible each morning, mainly in the mountain valleys but thick
cloud cover may limit this potential. Tropical system remnants could
bring widespread restrictions and rain to at least a part of the
area early next week, but confidence remains very low at this time.

&&

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

&&

$$

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