Carthage, South Dakota Weather Forecast Discussion

855
FXUS63 KFSD 181955
AFDFSD
Area Forecast Discussion
National Weather Service Sioux Falls SD
255 PM CDT Thu Sep 18 2025
.KEY MESSAGES...
- Scattered showers and isolated storms will continue to be
  possible into the weekend, with the best chances (30-60%) west
  of Hwy 81 and in portion of NW Iowa this afternoon/evening,
  and across Minnesota Friday.
- Scattered showers/isolated storms possible again Sunday, but
  details are uncertain.
- Near-to-slightly below normal temperatures are expected into
  the weekend, with a slight warm-up possible early next week.
&&
.DISCUSSION...
Issued at 255 PM CDT Thu Sep 18 2025
LATE AFTERNOON THROUGH SATURDAY: A nearly stacked mid-upper
level low will continue to slowly spin over the Dakotas and
into Minnesota over the next couple of days. This will keep the
weather unsettled across our area into at least early Friday
evening. Will continue to see shallow showers across our western
counties into this evening, but expect coverage to decrease
after sunset with focus then shifting to the eastern half of the
forecast area as a modest wave rotates through the southeast
periphery of the main trough. This should spread showers and a
few embedded thunderstorms northward across areas along/east of
I-29 this evening/overnight. Limited instability/shear should
keep any severe threat away from our forecast area, but nearly
moist adiabatic lapse rates and decent moisture depth could lead
to more efficient rainfall. Pockets of 0.50" rain or more are
possible through Friday evening, mainly east through north of
Sioux Falls.
As the system slides farther northeast toward the western Great
Lakes later Friday night/Saturday, its influence will decrease
across our forecast area. This should allow for drier conditions
most areas for the first half of the weekend, with seasonable
highs in the lower-mid 70s (slightly warmer than Friday for most
areas).
SUNDAY-MONDAY: Broad troughiness lingers into Sunday, followed
by weak upper ridging early next week. Confidence in details
during this period begins to wane as model solutions show less
agreement. However, we could still see occasional showers or
isolated storms as waves rotate through the region. General
model consensus shows some increase in instability by Sunday,
though profiles show tall/skinny CAPE profiles with mid-level
lapse rates below 7C/km. Shear, while still on the weaker side,
does increase over what we currently have with a low (20-30%)
joint probability of CAPE > 500J/kg where shear > 30kt. Given
uncertainty in wave timing and weak mid-level lapse rates,
severe weather risk appears low, but we may have to monitor over
the next couple of days as some machine-learning outlooks do
indicate a low (5%) severe risk for the Sunday/Sunday night
period.
TUESDAY ONWARD: Very low confidence as models diverge further in
handling of the upper pattern. If faster upper trough solutions
pan out (similar to 12Z operational ECMWF/Canadian, we would
trend drier for mid-late week. However, a slower evolution to
the upper pattern (as seen in the 12Z operational GFS) would
result in rain chances lingering into the middle of next week
before drying out. Made no changes to the mid-long range NBM
pops, which currently favors the faster/drier solutions. But
changes may develop if models trend more toward the slower GFS
solution.
&&
.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1255 PM CDT Thu Sep 18 2025
MVFR ceilings persist near/west of US Highway 81 at the start
of this period with scattered showers resulting in occasional
MVFR visibility as well. Although shower chances will decrease
after sunset, MVFR to IFR ceilings are expected to persist.
VFR conditions more likely along and east of I-29 through this
evening. However scattered showers/isolated thunderstorms will
also become possible here, mainly during the evening/overnight,
lingering across east central SD/southwest MN Friday morning.
In addition to any showers, lower stratus and areas of fog will
result in deteriorating ceiling/visibility for the latter half
of the TAF period.
While isolated thunder is possible, chances are too low to
include mention in any of the TAFs at this time.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&
$$
DISCUSSION...JH
AVIATION...JH

NWS FSD Office Area Forecast Discussion