Johnston, South Carolina Weather Forecast Discussion

450
FXUS62 KCAE 261033
AFDCAE
Area Forecast Discussion
National Weather Service Columbia SC
633 AM EDT Fri Sep 26 2025
.SYNOPSIS...
Scattered showers and storms today as a cold front approaches
the area, with potential for locally heavy rain. The rain
chances persist into the weekend and early next week with lower
temperatures. A potential tropical system could approach the
coast early in the week as well.
&&
.NEAR TERM /THROUGH TONIGHT/...
Key message(s):
- Scattered showers and storms today, mainly in the late
  afternoon and evening.
- There is potential for some locally heavy rain.
Today and tonight: An upper trough and associated surface front
are currently sitting over the Tennessee Valley and are
crawling eastward. Expect this trend to continue through the day
and into tonight. Given their current location and latest model
guidance trends, the advancement is looking slower than it did
yesterday at this time. This affects the forecast somewhat for
today. Expect a round of showers this morning, mainly for the
western portions of the forecast area. Another round of
scattered showers and storms is anticipated to move into the
area this afternoon into the evening. In addition, the highest
chances for rain are now over the eastern portions of the
forecast area. There is plenty of moisture available ahead of
the frontal boundary, with PWATs currently in the 1.6-1.8" range
and are forecast to slowly increase later in the day. Values
could top 2" in the eastern Midlands by this evening. The latest
HREF LPMM forecast is showing pockets of 2-4" in the eastern
portions of the forecast area, mainly this evening into the
overnight hours. This makes sense that there is this potential
given a few things. In addition to the high PWATs and slow
moving front, upper level flow is expected to be generally
parallel with the surface front, leading to training and/or slow
moving cells. The forecast soundings also show long and skinny
CAPE, indicative of heavy rain threat. Therefore, it is
reasonable to expect some locally heavy rain, mainly in the
eastern Midlands and PeeDee. Despite the dry conditions, if some
heavy rain occurred over some of the more urban land use areas
like Orangeburg or Manning, there is potential for some flash
flooding.
&&
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
Key message(s):
- Widespread showers and embedded thunderstorms expected during
  the day on Saturday.
- Below normal temps expected with cloud cover and rain across
  the area.
Our trough will continue to slowly shift eastward through Saturday
and Saturday night. The trough axis is forecast to be neutrally
tilted at the beginning of the period, gradually taking on a
negative tilt as we head forward in time. The result is that the
upper level jet streak will maintain a right-entrance region
across the Carolinas. The trend the past couple of days has been
for the overall features to slow down a bit, and if this trend
continues, we should continue to see favorable lift across the
area for longer periods of time on Saturday and Saturday night.
Moisture is forecast to remain rich, especially early on the in
the day. With shortwaves passing through and the favorable jet
dynamics, we should see numerous showers/storms during this
period. Given high PWs and persistent rain chances tonight and
into Saturday, flash flooding is a possibility, with the eastern
CWA outlined in a Slight Risk for Excessive Rainfall.
Widespread clouds are expected, with highs remaining muted in
the upper 70s to around 80. Rain chances will likely diminish by
Saturday night as the initial trough axis moves to our
northeast, with the best moisture following suit. So while
clouds may hang continue to hang around, we should at least lose
rain chances by Sunday morning. Look for lows in the mid to
upper 60s.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Key message(s):
- Highly uncertain forecast during the extended that will be
  dependent on Invest 94L, currently north of Hispaniola, and
  what, if any, impact it will have on the forecast area.
A complex, uncertain, and potentially impactful forecast is on tap
through early next week as a potential tropical cyclone develops in
the Bahamas and interacts with our upper level trough. To put it
kindly, guidance is struggling with the forecast in the Sunday-
Tuesday timeframe. This primarily owes to the complexity of the
synoptic scale setup, where multiple tropical systems are forecast
to be interacting with one another in addition to the tropical
cyclone nearest us interacting with our upper level trough. Zooming
out, Sunday is probably one of the crux days of this forecast as
invest 94L (currently north of Hispanola & currently organizing) is
expected to be nearly a TC by this point. Upper level trough axis is
forecast to stretch from the southern Appalachians through the
eastern Gulf early on Sunday, gradually taking on a slightly more
negative tilt and interacting more with 94L as it traverses the
Bahamas.
From here, guidance is really split on what happens. Humberto,
forecast to be a powerful Major Hurricane by Sunday, will begin to
make its influence known and felt as it moves north of Puerto
Rico, into the realm of potential interaction with 94L. It is
difficult to pin down just how these three features will
interact, not to mention other synoptic features such as the
intensity of the Central Atlantic ridge that is steering
Humberto currently. So looking at individual solutions, and even
ensemble means and solutions, is very challenging to do right
now because this is one of the more uniquely difficult synoptic
setups that I can remember forecasting. As such, saying anything
more than "Impacts are highly uncertain" would be speculation
more than forecasting. The presence of a tropical cyclone near
the southeastern US, plus a trough overhead, does favor heavy
rainfall somewhere over the Carolinas early next week as
favorable moisture advection can be easily created with a plume
of tropical moisture to our southeast. But until 94L actually
becomes a tropical cyclone, it will be difficult to say anything
more than that as far as impacts go. Please stay tuned to the
forecast, as this forecast is poised to go through multiple
iterations before we really get a solid idea of what to expect.
One thing that can be said - by the end of the period, we are
likely going to be staring down our first real taste of fall. An
anomalously strong Canadian high pressure is forecast by all
pieces of guidance to push into the northeastern US by
Thursday/Friday, ridging into the Mid-Atlantic and Carolinas by
this point. This should result in below normal temps arriving to
the area.
&&
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
Possible restrictions this morning and again this
afternoon/evening as scattered showers and storms move through.
Radar imagery shows scattered showers moving through the western
half of the forecast area for the start of the TAF period. So,
the Augusta and Columbia terminals are expected to see periodic
showers this morning. AGS and DNL are likely to see periodic
IFR cigs through about 15z as well, while CAE and CUB could see
some MVFR cigs during this time. Cigs should improve to VFR
after about 15z until the next round of showers and storms
arrives this afternoon and into tonight, when restrictions are
anticipated again. Have held steady with a PROB30 group for
thunder beginning at 18z and predominant showers starting at
00z. Ceilings could drop to MVFR or possibly IFR after 06z, but
confidence isn`t high enough to include at this time. Generally
southwest winds around 5-7 kts can be expected through 00z
before becoming light and variable to calm. The exception is the
potential for gusty winds near showers or storms this
afternoon.
EXTENDED AVIATION OUTLOOK...Deep moisture remains in place this
weekend leading to likely rain chances and possible widespread
restrictions.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
SC...None.
GA...None.
&&
$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...

NWS CAE Office Area Forecast Discussion