Anderson, South Carolina Weather Forecast Discussion

563
FXUS62 KGSP 240540
AFDGSP
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
140 AM EDT Wed Sep 24 2025
.SYNOPSIS...
An unsettled pattern emerges ahead of a cold front with multiple
rounds of showers and thunderstorms through the week and into the
weekend. Temperatures remain warm through Thursday before cooling
into more seasonable highs.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 1205 AM Wed: Upper pattern now features closed low near the
UP of Michigan and another one over the High Plains, embedded
within an open wave which will advance thru the mid-MS Valley
today, congealing into a single feature by tonight. Surface low
already present near the Ozarks will amplify as the latter wave
moves east. A zone of upper divergence and WAA is driving loosely
organized convection across KY/TN, with steering flow likely to
carry this activity by to our northwest this morning, similar to
what happened yesterday morning. A fleeting precip mention will
be carried thru daybreak near the TN border, but otherwise the
morning appears quiet. Cloud cover over portions of the mountains
should limit the extent of mountain valley fog.
A few pockets of upper divergence or vort blobs associated with
upstream convection may ride over the mountains during the early
daytime, but CIN still looks too much to expect initiation
then. Destabilization looks to occur diurnally on the usual
schedule. Dewpoints appear to remain higher today so LCLs lower and
coverage should be greater. CAMs still keep convection primarily
over the mountains, with SW`ly storm motion vectors suggesting
tracks parallel thereto. Overall diurnal instability is the
main driver for PoPs, aided by mechanical lift on SW flow. Some
DPVA arrives late in the afternoon and early evening. Skinny but
uninhibited elevated CAPE profiles are seen and so the mountain PoPs
linger into evening and expand slightly into the upper Piedmont. A
much more appreciable increase in upper forcing comes later in the
night as jet streak amplifies ahead of the approaching trough/low,
with a coherent area of upper divergence shifting over the mountains
and likely broader scale DPVA occurring at that time. Chances rise
to likely in the mountains and increase across the upper Piedmont
in the wee hours of Thu.
Continued WAA will allow the warming trend to continue another day;
some areas along and southeast of I-85 reach 90-92. GSP and CLT
still fall a few degrees shy of the daily records, and the record
at AVL is even farther out of reach.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Key Messages:
1) Unsettled pattern of showers and thunderstorms possible ahead of
a cold front.
2) Rainfall totals for both days range from 0.5-1" with locally
higher amounts possible in the mountains.
3) Cold front reaches the area and ushers in cooler temps by Friday
night.
As of 125 AM EDT Wednesday: Picking up on Thursday with model
guidance that is completely different than previous runs. There is
still an upper low across the Midwest, but it quickly gets
reabsorbed into the general flow with now a split trough feature
occurring that will affect the weather into the weekend. This
positively tilted trough on Thursday appears to get hung up amongst
all the model guidance (GFS/EURO/NAM), forming a new area of low
pressure through the end of the period. There still appears to be a
cold front approaching and that should still bring in cooler
temperatures by Friday night. It doesn`t appear to be a strong
frontal boundary as it too mixes out over the area, keeping the CWA
in a broad warm sector into Friday, contributing to more widespread
showers and thunderstorms. Looking at the parameters, there appears
to be a bit of instability present on Thursday and Friday
afternoons. Along with this, a light swath of DPVA could aid in
thunderstorm development as well. One major caveat and area for
uncertainty is how elongated and positively tilted the trough is
before it splits and a cutoff low forms, if this actually happens.
The model guidance, again, has not been consistent with this new
emerging split flow pattern. However, confidence in an unsettled
pattern of moisture advection and the possibility for multiple days
of showers and thunderstorms extending through and past the short
term, is increasing. As the front nears, expect PoP chances to be
categorical (76%-90%) across the mountains and eventually chance (60-
75%) elsewhere on Thursday into Thursday night. By Friday, again if
this low over the TN Valley occurs, PoPs would remain for the CWA in
the chance (56-74%) category. As far as QPF response, the
probability of receiving more than 1 inch of rainfall has increased
to 40-50% for the NC mountains (more the far western areas) and 

NWS GSP Office Area Forecast Discussion