350
FXUS63 KFSD 261756
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1256 PM CDT Sat Sep 26 2026

.KEY MESSAGES...

- Steady rain/drizzle exits off to the northeast through the
  afternoon. Scattered showers will redevelop this afternoon
  mainly east of the James River, but not everyone will get
  rain from this activity.

- Additional showers or storms look to redevelop in northwest
  Iowa this evening into the early overnight. Severe weather is
  not expected, but brief heavy downpours can be expected if a
  thunderstorm develops.

- Daytime temperatures remain below normal, but should climb
  closer to normal today for areas west of the James River, and
  then tomorrow and Monday for the whole area.

- After a brief break late Sunday into Monday, rain chances
  return Monday night into Tuesday. Pockets of heavier rainfall
  will again be the primary concern.

&&

.UPDATE...
Issued at 415 AM CDT Sat Sep 26 2026

Light to moderate showers located mainly east of the James River
as of 330 AM will slowly track east-northeast across the forecast
area through the morning. Could continue to see areas of drizzle
on the western edge of the rain, but with decreasing lift behind
the departing lead wave, drizzle coverage should likewise diminish
as we move toward midday-early afternoon. Any break from the rain
will be brief, especially in our eastern areas as a trailing wave
quickly slides across the region this evening. This stronger wave
could trigger a few thunderstorms with heavier rainfall rates.
However, severe weather risks are very low given lack of shear and
limited instability.

Stratus looks to remain persistent through tonight into Sunday
morning, with increased probabilities of fog later tonight into
Sunday morning as well. May see some breaks in the stratus by
Sunday afternoon, especially west of I-29 as the low level moist
layer thins a bit. However, with a continued moist east-northeast
flow, confidence is low regarding how far east any appreciable
sunshine will be seen and have generally trended higher than the
NBM in projected sky cover into Sunday.

Another system looks to move across the region later Monday into
Tuesday next week. Again, limited instability and shear will keep
severe weather risks low, but pockets of heavier rainfall will be
possible.

&&

.DISCUSSION...
Issued at 233 PM CDT Fri Sep 25 2026

An area of showers continues to move east-northeast across the
Highway 20 corridor in northwest Iowa. Some patchy drizzle will
be left in its wake. Elsewhere, patchy drizzle will continue to
occur as stratus remains in place across the area, though cloud
ceilings have risen a bit since this morning, making the
drizzle more patchy in nature. Showers look to develop along the
Missouri River Valley and lift northward starting late this
afternoon/early evening and continuing into the early overnight
period as warm air advection increases across the area. An
upper level wave will pivot into the area overnight as well,
which will help increase the coverage of this activity. Plenty
of moisture in place as PWATs increase to around 1.75+",
highest generally near and east of I-29. On top of this, there
will may be some elevated instability around 300 J/kg that
could allow for isolated rumbles of thunder. This activity will
gradually shift east-northeast through Saturday morning, with
additional patches of drizzle likely behind these showers. In
terms of rainfall amounts through tomorrow morning, we look to
generally see around 0.75-1.25" near and east of I-29, with
lesser amounts the farther west you go across the area. A few
spots could see upwards of an 1.5-2" (20-30% chance) if
multiple pockets of heavy rain move over one area. But with
training convection not expected, flash flooding concerns remain
very low.

Will have to watch Saturday afternoon and evening as a secondary
area of mid level vorticity moves across the area. There may be
enough daytime heating near and west of I-29 to allow for
around 500-750+ J/kg of CAPE to develop. There is a warm layer
around 700 mb that any rising parcels will have to fight against
before a thunderstorm could develop, but the lift provided by
the upper wave may be enough to overcome it, especially closer
to I-29 where this warm layer is a little weaker according to
soundings. Should it break the cap, a few thunderstorms may be
able to develop. Severe weather is not expected as weak shear
will be in place. So lightning and brief heavy downpours would
be the main threat if any of this development were to occur
(20% chance). Might be a better chance (30-40%) of this
development over northwest Iowa Saturday evening as an 850 mb
front moves into the area. Slightly better shear around 20 kts
will be place at that time, so perhaps a more organized storm is
possible, but still not enough for a severe weather concern.

This 850 mb front will bring a very brief period of northerly
winds overnight Saturday into Sunday, which may help thin the
stratus a little bit. But then fog will likely develop as ample
moisture near and at the surface will be still be present. Any
fog and stratus will linger into Sunday morning, but any stratus
is looking more shallow than what we`ve seen compared to the
past couple of days so drizzle appears unlikely. With the more
shallow stratus in place, should be able to mix out some of it
Sunday afternoon, allowing for a few periods of sunshine and
warmer temperatures, with highs in the upper 60s to lower 70s.
This period of drier weather will likely be brief though,
because our next storm system is set to move into the area
Monday night into Tuesday. Latest LREF probabilities for this
time period shows around a 20-30% chance of at least an inch of
rain mainly south of I-90.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1249 PM CDT Sat Sep 26 2026

An area of steady light to moderate rain exits off to the
northeast to start the period, though some drizzle will continue
in its wake. Starting to see clouds scatter out in portions of
South Dakota west of the James River early this afternoon,
which will likely be confined to these areas. However, stratus
where it does stick around with lift a little bit through the
afternoon, with the return of MVFR cigs expected west of I-29,
with perhaps some brief pockets of MVFR cigs along the I-29
corridor late this afternoon. Cigs will drop area-wide once
again tonight, and fog looks to develop, some of which could be
locally dense at times. Fog should lift by the mid-morning
Sunday, though IFR stratus likely lingers after it to end the
period.

In terms of rain chances this evening and overnight, a few showers
and isolated thunderstorms look to develop mainly near and east of I-
29, with the better chances (20-40%) of a thunderstorm over
northwest Iowa, northeast Nebraska, and far southern Minnesota.
Southeasterly winds will gradually diminish through the afternoon
and evening, with winds becoming light and variable to calm
overnight. Light northeasterly winds will end the period during the
late morning.

&&

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

&&

$$

UPDATE...JH
DISCUSSION...Samet
AVIATION...Samet