938
FXUS63 KFSD 231132
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
632 AM CDT Sun Aug 23 2026

.KEY MESSAGES...

- Scattered showers and a few storms are likely early this
  morning in south-central South Dakota, with some lingering
  activity possible into the afternoon. Severe weather is not
  expected, but locally heavy rainfall will be possible during
  any afternoon storm.

- The next better chance for showers and storms across a wider
  part of the area is tonight (50-70%). Locally heavy rain and
  isolated severe storms are possible.

- Otherwise most days through next week will see highs in the
  80s and lows in the upper 50s to lower 60s.

&&

.UPDATE...
Issued at 415 AM CDT Sun Aug 23 2026

Forecast remains on track this morning with an area of light
showers and trailing thunderstorms moving slowly east across
south-central South Dakota. Instability is limited east of the
Missouri River until mid-late afternoon, so anticipate general
weakening as activity attempts to move east this morning.

Still seeing some signals in 00Z/06Z guidance pointing to a
potential for locally heavy rainfall tonight. The question is
exactly where it may materialize as there has been little run
to run consistency showing where a line of slow-moving/training
storms may set up. Some solutions place this near to just north
of the Missouri River, while others shift the risk farther south
into north-central Nebraska. This leads to a lower confidence
forecast for tonight, both in terms of the isolated severe risk
and heavy rain potential addressed in previous discussions below.

Issued at 845 PM CDT Sat Aug 22 2026

No major changes to the forecast tonight and tomorrow. Mid to
high level clouds are moving into south-central South Dakota
associated with our next weak wave moving in. These clouds will
continue pushing east-southeastward through the night, and the
aforementioned wave will help set off some showers and weak
thunderstorms starting in south-central South Dakota early
tomorrow morning with this activity gradually spread east-
southeastward through the day on Sunday. As it moves eastward,
it will outrun any appreciable instability and become just hit
or miss light showers/sprinkles as it approaches I-29.

Heavy rain looks to be the main threat heading into Sunday
night as the low level jet kicks up and sets off more elevated
thunderstorms with the aid of an upper wave moving in from the
northwest. With the potential of multiple updrafts going up
around the same time, there will be plenty of competition for
the strongest updraft and this will help limit a severe weather
risk. However, if one or two storms can go more isolated and
become a more dominant updraft, then perhaps some large hail
will be possible given effective shear values around 40-45 kts.
Freezing levels will be quite high though, so even if an updraft
can sustain itself, hailstones will have a pretty deep warm
layer to go through before it were to reach the surface.

&&

.DISCUSSION...
Issued at 142 PM CDT Sat Aug 22 2026

A quiet night is ahead as high pressure drifts east. Southerly flow
will develop in central SD later tonight and become more
established across the area through Sunday. The light winds will
allow temperatures to fall into the lower 50s, especially east of I-
29.

The upper level wave responsible for the low level winds turning
southerly will move into central SD tomorrow morning, and eastward
and southeast from there through the day. With fairly stout low to
mid level dry air, mainly an increase in cloud cover is expected
through the morning. The exception will be south central SD where
enough moisture may allow for 500-1000 J/kg of elevated CAPE, which
will support some spotty showers and thunderstorms. Severe weather
is not expected.

Lift will gradually increase through the day into Sunday night,
when a moderately stronger LLJ focuses on the area. Given fairly
weak shear and CAPE values generally under 1000 J/kg, severe weather
looks unlikely. However with a freezing level around 13 kft, locally
heavy rain will be possible. Not much agreement on the location of
the heavier rain with the models pretty inconsistently placing the
mid level wave across the area. Some hints that the LLJ will focus
somewhere on the SD side, but confidence is low.

This wave moves out of the area on Monday but another weaker wave
moves by to the north on Monday night and brings a small increase in
warm air advection, which could spark a few showers and
thunderstorms.

Mainly northwest flow aloft continues Tuesday into next weekend. This
will bring periodic small chances for showers and thunderstorms
throughout the week with little agreement on exactly when. Otherwise
lows should mainly be from the mid 50s to mid 60s with highs in the
80s.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 632 AM CDT Sun Aug 23 2026

VFR conditions should be prevalent across the forecast area
through today with a possible exception of occasional MVFR
visibility in rain/isolated thunderstorms toward south-central
South Dakota.

Growing chances for showers and storms moves east after sunset,
potentially impacting TAF sites after 24/04Z-06Z. This could
bring a brief period of MVFR visibility, though confidence in
timing is on the low side so will stick with PROB30 for now.

&&

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

&&

$$

UPDATE...JH/Samet
DISCUSSION...08
AVIATION...JH