473
FXUS63 KFSD 280548
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1248 AM CDT Mon Sep 28 2026

.KEY MESSAGES...

- Additional areas of fog are expected tonight especially east
  of I-29. Locally dense patches could lead to visibilities as
  low as a half mile at times.

- Pockets of drizzle will also be possible mainly east of I-29
  with mainly light accumulations expected.

- Widespread showers with a few isolated thunderstorms will
  likely likely return from late Monday night into Tuesday.
  While severe weather is not expected, locally heavy rainfall
  will be the primary concern.

- Additional rain may impacts areas especially south of I-90
  through the day on Thursday. Prolonged rainfall on top of
  recent rainfall could lead to some flooding concerns. Keep up
  to date with the latest forecast.

&&

.UPDATE...
Issued at 940 PM CDT Sun Sep 27 2026

Another dreary night is expected as the holes in the stratus
continue to fill in this evening. Similar to last night, additional
areas of fog and drizzle are expected as ceiling lower with the
cooling temperatures. Fog-wise, can`t completely rule out more
widespread of coverage given the smaller dew point depressions and
lighter surface winds with the surface high. However, locally dense
patches will be a bit more scattered with most short-range guidance
focusing in on portions of southwestern MN and northwestern IA.
Either way, we`ll have to continue monitoring surface observations
and web camera as a dense fog advisory will likely be needed tonight
for areas east of I-29. Otherwise, should see most of this fog
gradually erode by mid to late morning (9am-11am).

Overall, Monday should be mostly a carbon copy of today with highs
mainly in the low to mid 70s. The main difference comes with the
breezier conditions and increasing precipitation chances. While were
still on track for a few sprinkles by Monday afternoon, the main
push of precipitation won`t likely occur until after midnight into
Tuesday morning as the better forcing and moisture arrives in our
western-most counties. While severe weather is not expected, locally
heavy rainfall will be the main threat as PWATs (1.25"-1.50")
approach the top 0.5 percentile of ensemble guidance according the
ESAT tables. Expect these increased rain chances to continue working
their way across the area throughout the day on Tuesday with
additional rainfall expected on Wednesday. Lastly, while overall
amounts are still a bit uncertain; the highest accumulations will
likely set up somewhere east of a Tyndall to Sioux Falls to
Marshall, MN line with pockets of 1-2 inches over a 24-48 hour
period possible.

&&

.DISCUSSION...
Issued at 248 PM CDT Sun Sep 27 2026

Finally starting to see some stratus eroding and leading
to some sunshine in parts of the area this afternoon. We may
continue to see some erosion of the stratus so long as the sun is up
as the relatively high sun angle (at least compared to winter)
seems to be able to thin some of these lower clouds. Soundings
still show some shallow instability within the lower cloud layer
though, so we may continue to see some sprinkles to very light
showers develop mainly through the afternoon and early evening.
A few returns have popped up on radar west of the James River,
but the lack of droplets on area cameras supports the idea that
any rain will be very light in nature.

Stratus should build back in through the overnight hours along with
some more fog. Not expecting fog to be as widespread or as
dense as it was earlier this morning, but still locally dense
fog will be possible mainly near and east of I-29 as this is
where winds will be lightest. Models are a bit split on how
shallow this stratus that develops tonight will be, so there
remains some uncertainty as to if there will be some drizzle or
not tomorrow morning. Enough confidence to mention at least some
patchy drizzle during the morning commute so you may have to
deal with some drizzle on your way to work or school.
Temperatures will once again be slow to fall off through the
overnight hours, especially after the low clouds redevelop and
thicken late tonight. Think most of us will end up in the lower
60s for morning lows, though some pockets of upper 50s will be
possible mainly near and east of I-29. Raised the NBM a bit by
blending in some CONSAll to minimum temperatures given the
returning southerly flow expected overnight.

Monday is looking to be a similar day to today. We`ll start off with
some low stratus that will gradually become more shallow into the
early afternoon. At the same, there will once again be a shallow
layer of instability to allow for some more sprinkles or light rain
showers especially into the afternoon hours. At the same time, a
trough will be digging towards the Desert Southwest and send an
initial area of vorticity into the Northern Plains through the day.
This should keep the more organized rain showers and thunderstorms
tomorrow north of the area, though can`t rule out some of this
activity clipping our far western areas depending on the ultimate
track of the wave. If this activity were to clip the area,
thunderstorms appear unlikely as any parcels that rise will only
have access to decent instability if it could overcome a strong
cap around the 850/700 mb layer, which appears unlikely with
the better forcing expected to our north and west. Also similar
to today, most high temperatures will be in the upper-60s to
lower-70s, perhaps slightly warmer west of the James.

The aforementioned Desert Southwest trough will send another upper
wave into the region Monday night into Tuesday, this time much
closer to home. With that, rain and storms are expected (70-90+%)
especially late Monday night into the day on Tuesday. Modest shear
will be in place, but instability looks fairly weak and so severe
weather looks unlikely. Heavy rain appears to be the main threat
with this system, especially when looking a bit ahead as the main
trough closes off and absorbs the remnants of Hurricane Polo
and very slowly moves eastward. This will mean that the trough
continues to send upper waves into our region and so higher rain
chances may continue especially south of I-90 through the day
on Wednesday and potentially as late as into Thursday morning.
Based on the position of the trough/closed upper low, the better
instability will likely stay south of the area. So instead of
any convectively driven flooding concerns, will have to watch
how rivers respond to prolonged rain on top of the rain we`ve
already seen this past week. The latest excessive rainfall
outlooks from the WPC paint the southeastern half of the area
with level 2 of 4 Slight Risks for Tuesday and Wednesday, so
continue to monitor the forecasts for the latest information.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1240 AM CDT Mon Sep 28 2026

Mainly VFR conditions with occasional MVFR to LIFR conditions
continue this evening. Taking a look at satellite imagery, we`re
starting to see the MVFR to IFR stratus deck thin and in some
parts clear west of I-29 surprisingly. Given the current
trends, thinking we should see things gradually continue to
clear out east of I-29 overnight. When this occurs, IFR to LIFR
fog will be the main concern especially across southwestern MN
into Monday morning. With this in mind, kept some patchy fog in
KFSD and KSUX with some potential for pockets of VFR drizzle.
Lastly, light and variable winds will become more southeasterly
into Monday morning with gusts between 20-30 mph into Monday
afternoon.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.

&&

$$

UPDATE...05
DISCUSSION...Samet
AVIATION...05