638
FXUS63 KFSD 240547
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1247 AM CDT Mon Aug 24 2026

.KEY MESSAGES...

- Showers and storms progress eastward into this morning.
  Further severe weather risks are very low, but locally heavy
  rain is expected under any thunderstorm. However, the risk for
  flash flooding is very low as well.

- Monday evening and night could see an isolated severe storm,
  with the better chances in central SD and also near highway
  14.

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

&&

.UPDATE...
Issued at 902 PM CDT Sun Aug 23 2026

A weak area of convergence extending from roughly Ivanhoe, MN
to Spirit Lake, IA may produce a sprinkle of two this evening,
but the main area to watch will be in south-central South Dakota
after midnight when the low level jet cranks up to around 30-
35 kts and helps develop showers and storms.

Elevated instability values have trended up for tonight;
however, the layers with access to the most CAPE will have less
shear to work with and this imbalance will limit any severe
weather potential. With the LLJ in place and drifting eastward,
additional showers and storms will develop, increasing
competition between updrafts which will also help limit the
severe potential. Not to mention instability and shear will also
be further decreasing as showers and storms move east-southeast
into the early morning hours. All that to say, the only
reasonable window for a storm to perhaps produce quarter-sized
hail will be the initial development around 1-2 am in Gregory
County, with any severe threat rapidly diminishing as new
showers/storms develop and push east-southeast.

Timing for shower and storms have also shifted a bit later in the
latest guidance, with activity likely not reaching the I-29 corridor
until closer to 5 am and the heavier showers now not pushing south
of the area until closer to the 7-9 am time frame. Locally heavy
rainfall is expected with any storms given high PWATs pushing 1.75+"
but activity should be progressive enough to preclude any flooding
concerns. A few pockets of 1-1.25" of rain will be possible where
the strongest storms move over with very low chances (<5%) of a
spot picking up 2" if a multiple storms go over an area.

&&

.DISCUSSION...
Issued at 237 PM CDT Sun Aug 23 2026

A pair of waves are affecting the area, or nearby, today. The first
is moving southeast through Nebraska and is keeping any instability
to the south and west bottled up. Model soundings not hinting at a
whole lot of activity this afternoon, with a fairly dry and stable
air mass in place.

Tonight a second wave will pass by to the north and will swing a
little bit of mid level moisture into the area. As this moisture
moves in, some weak elevated instability, likely 500-750 J/kg CAPE
develops. This will support some scattered shower and isolated
thunderstorm activity, but for now severe weather looks
unlikely. A few pockets of heavier rain are also possible, but
also trending downward.

Monday will see temperatures warm a bit with humidity likely to
increase as well. This is in response to strengthening southerly
flow as a stronger wave moves east along the Canadian border. This
will increase instability, especially to the northwest of the area,
and should bring scattered thunderstorms to parts of central SD and
near the highway 14 corridor. With the potential for about 1000-1500
J/kg CAPE and decent unidirectional shear, and isolated severe storm
will be possible in these locations. One area to watch will be near
northwest IA late Monday afternoon and evening where there are some
hints the cap could weaken a bit as elevated moisture advection
bring some instability to that area. Low confidence, but something
to monitor.

Northwest flow aloft Tuesday into the weekend will keep seasonally
warm temperatures in place with highs in the 80s and lows from the
upper 50s to mid 60s. Starting to see a little more consistency on
the next better chance for showers and thunderstorms on Friday. The
latest Canadian, GEFS and EC ensembles all indicate about a 30-5-
percent chance for a tenth of an inch or more of precipitation.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1239 AM CDT Mon Aug 24 2026

Scattered showers and thunderstorms have developed in central
South Dakota and will generally push east-southeastward through the
rest of the night into the early morning hours today. Some
lingering showers and thundershowers will continue to be
possible through the rest of Monday morning mainly east of I-29
as well. Some guidance has also consistently been hinting at
some MVFR stratus developing behind the main wave of
showers/storms this morning mainly north of I-90. Confidence in
this potential is on the lower side, but enough signals to
include it at KHON.

By this evening, additional thunderstorms will develop off to our
west, though uncertainty is high regarding how far storms are
able to progress east into our area if at all. For this reason,
opted to exclude mention of this at KHON at this time. Winds
will be mainly out of the south-southeast today, gusting up to
20 kts at times. Winds will gradually diminish towards the end
of the period outside of any thunderstorms.

&&

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

&&

$$

UPDATE...Samet
DISCUSSION...08
AVIATION...Samet