406
FXUS63 KFSD 130229
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
929 PM CDT Wed Aug 12 2026

.KEY MESSAGES...

- Showers and storms are expected again tonight into Thursday
  morning. The main threat is the potential for an MCS to pass
  through the highway-20 corridor with strong wind gusts up to
  70 mph.

- Locally heavy rain is also possible if storms can train over
  an individual area, especially if this occurs over an urban
  location.

- Areas of dense fog and low stratus may form again late tonight
  into Wednesday morning, though confidence in coverage is low.


- Cloud cover and cooler temperatures move in for Thursday into
  the weekend. Periodic showers and storms expected. Humidity
  lingers.

&&

.UPDATE...
Issued at 928 PM CDT Wed Aug 12 2026

Showers and an isolated thunderstorm or two is beginning to push
into the forecast area from the west. Instability values remain
around 1,000 to 1,500 J/kg across the bulk of the area. However,
latest guidance has been beginning to trend down instability values
for locations north of highway-20. That said, this does not rule out
a potential isolated strong to perhaps severe storm later during the
overnight hours that could be capable of quarter size hail and
strong winds to 60 mph. A few hi-res models have been consistent in
showing a second area of thunderstorms developing near and north of
I-90. These storms could pose more of a heavy rain threat along side
the low end severe threat. Especially with a westerly mean wind in
place, some training could occur. If this training were to occur
then isolated flash flooding would be possible, mainly in urban
areas.

The latest hi-res models remain on track with transitioning the
current convection across western Nebraska into an MCS. This MCS
will push eastwards on the elevated front. Some uncertainty remains
regarding just how far north this MCS may track. The furthest north
solutions bring it into the highway-20 corridor while the bulk of
the guidance keeps it just south of the forecast area. If this MCS
does follow the northern track by anchoring closer to the 700mb
front, then strong winds up to 70 mph will be possible in this area.
At the same time, this same area look to be the most likely to see
potential flooding. This remains contingent upon a northerly track
but still applies to mainly urban areas. This MCS will push east of
the area by the early morning hours, leaving light to perhaps
moderate rain in its wake. A few of the models suggest that a wake
low could develop behind the departing MCS. Tough to assign a
probability to this potential but something to keep an eye on.

The next chance for rain will come late Thursday night into Friday
morning mainly across northwest Iowa. This is in response to the low
level jet restrengthening and pushing a bit further northwards.
Vertical shear looks to be much weaker so severe storms are not
likely.

&&

.DISCUSSION...
Issued at 121 PM CDT Wed Aug 12 2026

A pair of waves move onto the Plains tonight. The first will be
associated with the right entrance region of the upper jet to the
northwest. This may bring some some stronger storms to central SD
later this evening. An isolated severe storm will be possible. Later
tonight a more subtropical wave moves from CO into northern NE and
may interact with a much more unstable environment. If this develops
it will likely become linear with heavy rain and wind gusts to
around 70 mph likely. The better chances for this coming together
will be near the Missouri River into northwest IA, likely from about
2 am to 7 am. CAPE values likely running about 20000-4000 J/kg with
moderate deep layer shear.

Once this activity exits the area, fairly stable air settles in for
much of Thursday into Thursday evening. Thursday morning may see some
low stratus and patchy fog, with these clouds lifting a bit but
likely lingering through the day. This should limit warming a bit
with highs likely remaining in the 70s. However with these cooler
temperatures will not come a drop in humidity with dew points still
likely in the mid 60s to lower 70s.

Later Thursday night into Friday morning a weak wave will lift north
into the area and should bring weak to moderate warm air advection
in the low to mid levels. With the potential for maybe 1000 J/kg
CAPE a few thunderstorms will be possible, with the better chances in
northeast NE and northwest IA. Severe weather is unlikely but local
heavy downpours are possible.

Friday afternoon and Friday night weak upper level ridging will
build and likely suppress any convective activity. However Saturday
into Saturday evening showers and thunderstorms will likely
redevelop with very isolated severe storms and locally heavy rain
possible.

Faster northwest flow aloft will be north of the area Monday through
Wednesday next week. This will keep a slightly cool air mass in
place during this time with highs generally from 75 to 85 each day.
Periodic weak waves will move through and bring chances for showers
and thunderstorms with low confidence on strength and timing right
now.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 644 PM CDT Wed Aug 12 2026

Latest satellite shows mid and high level clouds overspreading the
area to begin the TAF period. Currently, any showers and storms
remain mainly west river. These showers and storms will push
eastwards through the evening hours and reach the forecast area
during the late evening to early overnight time period. Some
uncertainty remains regarding how expansive the showers and storms
will be so have included PROB30 groups in all TAFs. The bulk of the
rain looks to fall south of I-90 at this time. Ceilings look to also
lower to MVFR/IFR levels both while rain is falling and after the
rain moves east. Visibilities look to fall to MVFR levels while it
is raining but could be lower in localized areas.

Chances for rain will be coming to an end through the morning hours.
However, low level stratus may linger around for longer than
currently anticipated. Will see how tonight`s activity plays out
before potentially extending the timeframe of the low level stratus.
Otherwise easterly winds will finish out the TAF period.

&&

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

&&

$$

UPDATE...Meyers
DISCUSSION...08
AVIATION...Meyers