232
FXUS63 KFSD 181738
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1238 PM CDT Mon Aug 18 2025

.KEY MESSAGES...

- A few strong to severe storms are possible this evening mainly
  along and south of the Missouri River. Ping pong ball-sized
  hail and 60 mph wind gusts are the threats if a storm develops
  locally.

- Warm and very humid again for Monday with afternoon heat
  indices in the mid-90s to around 100, warmest towards the
  Missouri River into northwest Iowa.

- A break from this active pattern is expected mid-week as
  after this evening, the next potential for storms is not until
  Thursday night. Confidence on details for Thursday night is
  low at this time.

&&

.DISCUSSION...
Issued at 416 AM CDT Mon Aug 18 2025

Scattered showers and storms continue to push eastward early
this morning across mainly northwest Iowa and southwest
Minnesota, bringing with it a threat of lightning and heavy
rain. Storms are generally moving fast enough to avoid flash
flooding issues, but areas of southwest Minnesota that were
inundated with rainfall last night will be at risk for
additional flash flooding, especially if those areas were to
pick up at least and inch to an inch and half per hour. This is
looking less and less likely by the hour as the heaviest rain
continues pushing off to our east through daybreak. There`s also
been some training convection overnight over parts of northwest
Iowa, which could lead to some flooding as well. Patchy fog
will be possible in western portions of the Highway-14 corridor
where rain cleared out first overnight. That should start to
lift by 9 am.

We`ll start out in the upper-60s to low-70s Monday morning, with
highs in the afternoon expected to climb into the mid-80s to low-
90s. It`ll be another day where walking outside feels like you`re
running into a wall that`s made of humidity as dew points soar well
into the 70s across the area. This will lead to heat indices in the
mid-90s to low-100s, warmest closer to the Missouri River into
northwest Iowa. The lower-100 heat indices will likely last only an
hour or two, so opted for no heat headlines at this time.

A 500mb wave will dive south from western South Dakota into Nebraska
late Monday, which will be the focus of storm development heading
into Monday night. With the wave quickly diving into Nebraska, storm
chances locally will be a lot lower than compared to the past couple
of days and mainly confined to areas along and south of the Missouri
River. These areas will be characterized by 2000-3000 J/kg of MLCAPE
and 30 kts of bulk shear (potentially increasing to 35 kts in south-
central SD). A few strong to severe storms will be possible in this
environment, with ping pong ball sized hail and 60 mph winds the
main threats. Any storms that do develop locally look to quickly
dive south of the area overnight leading to what will likely be a
quiet Tuesday morning with temperatures falling into the mid-to-
upper-60s.

An upper-level high will wander around the Four Corners region
through the middle of the week, keeping things mostly quiet locally.
The next trough will dig out of southern Canada late Thursday into
Friday as an upper-low moves southeastward from northern Manitoba.
This could set off our next round of storms Thursday night, but
there is still a lot of uncertainty regarding the details of this
system. As this trough shifts east of the area into the weekend,
we`ll get stuck in another northwest flow pattern would could send
occasional waves of rain/storms through the weekend, though nothing
looks too impressive this far out. Seasonably warm conditions look
to continue through the work week, with cooler temperatures expected
into the weekend as high pressure settles in.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1237 PM CDT Mon Aug 18 2025

Latest satellite imagery shows some low level clouds mainly along
and north of I-90. These clouds are sitting at VFR/MVFR/IFR levels.
Should see gradual lifting and dissipation of these clouds thanks to
diurnal mixing. At the same time, a CU field is beginning to develop
south of I-90, mainly across parts of southeast South Dakota and
northwest Iowa. Could see the CU field mix out as drier air is mixed
to the surface. Light and variable winds are expected throughout the
vast majority of the period. This may lead to fog developing late
tonight into tomorrow morning. Currently thinking that the Buffalo
Ridge in southwest Minnesota is the most likely area to see fog
tonight. Have included BR in KFSDs TAF as of now but may nudge it
down to FG if confidence increases in fog potential. Otherwise,
light east/northeasterly winds will finish out the TAF period.

&&

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

&&

$$

DISCUSSION...Samet
AVIATION...Meyers