100
FXUS63 KFSD 300528
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1228 AM CDT Wed Sep 30 2026

.KEY MESSAGES...

- Widespread areas of fog will develop tonight mainly along and
  east of Highway-281. Locally dense patches could lead to
  visibilities as low as a quarter mile at times through
  Wednesday morning.

- Additional showers will lift through the U.S. Highway-20
  corridor in northwestern IA by Wednesday afternoon. Mainly
  light accumulations are expected.

- Drier conditions will temporarily return on Thursday and
  Friday with the potential for our next rain chances returning
  by Saturday.

&&

.UPDATE...
Issued at 946 PM CDT Tue Sep 29 2026

Taking a look across the area, cloud cover continues to gradually
clear from west to east this evening behind a departing cold front.
While we do still have some light returns across our far
southeastern zones, a drier sub-cloud layer has led to mostly virga
instead of light accumulations. As this activity clears this
evening, lightening surface winds and lingering low-level saturation
will likely lead to widespread fog development tonight. While there
is still some questions as to how far west things develop, short-
range guidance continues to show high levels of agreement in areas
along and east of Highway-281 being the focal point for development.

With visibilities of a mile or less expected at times, we`ll likely
need a dense fog advisory at some point. However, we`ll hold off for
now until development occurs over the next several hours. Either
way, make sure to give yourself some extra time when making those
morning commutes as rapid changes in visibility are expected. Most
of the fog should gradually erode by mid to late morning. Otherwise,
a slightly warmer day is ahead with highs in the low to mid 70s.
We`re still on track for a few additional showers mainly along the
Highway-20 corridor by Wednesday afternoon. While any resulting
accumulations will be mainly light, can`t completely rule out a
pocket of an additional 0.25" to 0.75" inch if some convectively
enhanced showers develop through Thursday morning.

&&

.DISCUSSION...
Issued at 238 PM CDT Tue Sep 29 2026

Regional radar as of 29.1930Z shows the majority of warm
advective rain showers have moved into areas south of U.S. Hwy
18 across southeast SD and northwest IA. These showers will
continue to move eastward into the late afternoon/early evening
with most areas drying out by 00Z. That said, some CAMs show
scattered convective activity re-developing along a trailing
surface boundary/front late this afternoon and evening mainly
along and south of a Yankton to Sioux Falls to Windom line. Area
soundings show some weak instability, so will keep chance
POPs/isolated thunder into the evening across far southeast SD
into northwest IA. Any lingering activity will diminish
overnight, although clouds will be slow to move out. Some
clearing across southeast SD will allow lows to drop into the
low to mid 50s, whereas temperatures will bottom out closer to
60 degrees for areas under cloud cover across northwest IA.

In addition, will need to watch for fog overnight. Given weak
near surface flow and ample boundary layer moisture from rain
today, could see rapid fog development if the broader cloud
shield dissipates or moves far enough east.

For Wednesday, a strong Four Corners closed low will begin to eject
east-northeastward, and with it will be remnant moisture from
Hurricane Polo. This is a very wet system for late September with
NAEFS PWATS above the 99th percentile. However, our southernmost
forecast area will be on the northern periphery of the highest
moisture as the surface low moves across the Central Plains and the
stationary front sets up across NE/IA. 00/06Z model runs last night
and now the 12Z suite this morning have trended south with the
highest QPF. There is likely to be a sharp gradient in rainfall,
ranging from amounts less than an inch to higher than 2-3 inches.
Areas north of U.S. Hwy 18 will likely remain dry all day. Current
trends suggest our forecast area will be on the lower end, but
given some lingering concern about a late model shift north,
will keep current Flood Watch in place and adjust as needed on
later shifts. Otherwise, Wednesday will be warm and mostly
cloudy with high temperatures in the low to mid 70s.

Some lingering showers are possible Thursday across northwest IA,
but the majority of the area will be dry with much needed dry
conditions continuing into Friday as surface high pressure moves
across the region. A cold frontal passage Wednesday night will also
usher in cooler air, keeping high temperatures Thurs/Fri mainly in
the 60s. As long as skies remain mostly clear, overnight lows will
dip into the mid to upper 40s.

Another weak wave moves through northwest flow aloft on Saturday,
bringing a 20-40 percent chance of showers to areas mainly north of
I-90. Synoptic 500 hPa flow begins to diverge between the major
models Sunday into early next week, but the consensus now is for dry
conditions with seasonable early October temperatures.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1215 AM CDT Wed Sep 30 2026

Mainly VFR conditions with occasional IFR to LIFR vsbys are
expected this TAF period. Taking a look at satellite imagery, we
continue to clear from west to east this evening with a few
spotty patches of fog developing. Expect fog development to
become more widespread after 06z as winds continue to decouple
and the inversion sets in. IFR to LIFR vsbys will then persist
across the area through about 15z-16z (10am-11am) before gradually
eroding with diurnal heating. Otherwise, light and variable
winds will persist for the rest of the TAF period. Lastly,
a few VFR showers will be possible near KSUX towards the end of
the TAF period. With this in mind, decided to add a PROB30 for
light rain through 06z.


&&

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

&&

$$

UPDATE...05
DISCUSSION...Rogers
AVIATION...05