225
FXUS63 KFSD 121135
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
635 AM CDT Sat Sep 12 2026

.KEY MESSAGES...

- Scattered showers will be possible on Sunday with mainly light
  accumulations.

- More widespread chances for showers and storms are expected
  from Sunday night into Monday. While the severe weather risk
  is low, locally heavy rainfall is expected especially along
  and east of I-29.

- Near to below normal temperatures will continue with highs
  mainly in the upper 60s to 70s.

&&

.UPDATE...
Issued at 422 AM CDT Sat Sep 12 2026

The forecast remains on track with mostly quiet conditions returning
behind the cold front. Besides a few lingering sprinkles during the
morning hours, should see the quieter conditions persist for the
rest of the day as highs peak in the low to mid 70s. We`re still on
track for more scattered rain chances (30%-50%) starting as early as
tonight as mid-level frontal forcing strengthens. While severe
weather is not expected, the wet and dreary conditions will hang
around for most of the day so make sure to keep a light jacket on
hand. Lastly, more concrete chances for showers and thunderstorms
return from Sunday night into Monday as the LLJ strengthens ahead of
an approaching wave. While the severe weather risk remains low,
ample saturation in the warm air advective regime could lead to
beneficial rainfall across most areas. Lastly, we`ll continue to see
more seasonable conditions continues into the midweek with highs
mainly in the upper 60s to mid 70s.

&&

.DISCUSSION...
Issued at 207 PM CDT Fri Sep 11 2026

Today winds will be southerly and strong, gusting to 30-40 mph with
areas along the Buffalo Ridge possibly seeing 45 mph gusts. This is
in response to an approaching upper wave and surface low pressure
system tightening the SPG. Winds will decrease in the evening, but
remain gusty as the front comes through. Highs today will be in the
low to mid 80s east of I-29, mid to upper 80s west of I-29, and in
the 90s west of the James River Valley. Through the day a narrow
plume of Theta-e will advect in warm and moist air. Instability will
increase in concert along and east of the plume. By mid-afternoon
1500-2500 J/kg of MUCAPE will be available. Steepening mid-
level lapse rates, 30-40 kts deep layer shear, and clock-wise
deeply curved hodographs all set the stage for strong to severe
thunderstorms this afternoon into the evening. This is outlined
in the SPC Day 1 Marginal (level 1 of 5) Risk. However,
uncertainty remains leading to lower confidence in this
forecast. Firstly, we are strongly capped across much of eastern
South Dakota, and western Minnesota and Iowa. Model soundings
and the 14Z CAMs guidance have begun to increase the amount of
moisture in the 850-750 mb layer. Beneath that layer air remains
very dry displaying a classic inverted "V". From here there are
two possible scenarios. The first scenario is that the cap
cannot be over come, and elevated storms form along the 850 mb
front south of I-90, and east of I-29 after 7 pm. These storms
may produce large hail to the size of a ping-pong ball (1.5"),
damaging wind gusts of 70 mph, and brief heavy rain. This is the
most likely scenario. The second scenario is the cap is
overcome and isolated surface based supercells form along and
east of Highway 81 after 5 pm. Surface based storms could
produce hail the size of a golf ball (1.75"), damaging wind
gusts to 70 mph, and brief heavy rain. In addition, though the
risk is low (<2%) a tornado cannot be ruled out. These storms
will grow upscale as they move east forming a broken line with
possible bowing segments. The threats then transition to large
hail and damaging winds. In either scenario, storms should be
east of the region by 1 am Saturday.

Highs Saturday will be cooler, in the low to mid 70s thanks to the
CAA behind the front. Winds will be northerly and light at 5-10 mph.
Scattered light, elevated showers are possible Saturday. These
should have very little impact and accumulations will be a trace to
a couple hundredths at best. Modest moisture return in the mid-
levels for Sunday will support stratus showers as a low amplitude
wave passes to the north of the CWA and WAA pushes in from the
south. Rain totals will be modest. LREF guidance indicates a less
than 50% chance for 0.25 inches of rain for areas north of Highway
20 through midnight. In addition to showers, highs for Sunday will
be cool, in the 60s.

Late Sunday night into early Monday morning an upper trough over the
Pacific Northwest will begin to move east. A surface lee trough and
low pressure will form along the east side of the northern Rockies.
This will eject out onto the central Plains and accelerate
northeast. A warm front will push out ahead of it with warm, moist
air pooling behind it. Shortly before sunrise the LLJ ramps up south
of the front, while at the same time a prefrontal trough takes shape
and passes through the region. The combination of this forcing and
warm moist air riding up over the established cold air over our
region will result in more showers and isolated thunderstorms. Long-
term guidance is in very low agreement on the convective
environment. While it is possible an isolated stronger to severe
storm may form, confidence at this time is low. Highs for Monday
will be slightly warmer than Sunday, in the 70s.

By late Monday evening into early Tuesday morning, the main upper
wave swings north over the region and the attendant cold front
will move through from the northwest to the southeast. This fast
moving system brings better chances for strong to severe
thunderstorms that will pass quickly into central Iowa. An
unsettled pattern will keep storm chances in our forecast
through the end of the week. Highs during this time will be 5-10
degrees cooler than average for this time of year, in the 60s
to low 70s.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 628 AM CDT Sat Sep 12 2026

VFR conditions will persist this TAF period. Besides some
morning sprinkles, additional showers will be possible from late
tonight into Sunday morning. With confidence continuing to
increase in this potential, decided to add in a PROB30 group to
each TAF site towards the end of the TAF period. Otherwise,
northwesterly winds will become marginally breezy this afternoon
before dropping off overnight.

&&

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

&&

$$

UPDATE...05
DISCUSSION...AJP
AVIATION...05