775
FXUS63 KFSD 120201
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
901 PM CDT Fri Sep 11 2026

.KEY MESSAGES...

- Isolated severe weather threat will wind down through
  midnight.

- Stratus showers are expected for Sunday. These are unlikely to
  be severe. Better chances for strong to severe storms exist
  late Sunday evening into Monday morning.

- An active pattern keeps periodic storm chances in our forecast
  for much of the upcoming week.

&&

.UPDATE...
Issued at 856 PM CDT Fri Sep 11 2026

Diurnally driven thunderstorms along a dry line ignited this
afternoon and are currently shifting southeast. While the
environment continues to point towards strong to very isolated
severe potential, updrafts thus far have struggled and remained
fairly pulsy. With the pulsy nature and a freezing level around
13000 feet, larger hail has been hard to come by. A few
locations received a little hail, but less than quarter size.
Once the ongoing convection shifts southeast between about 11 pm
to midnight, the threat for thunderstorms will come to an end as
more stable air moves in behind.

&&

.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 /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 646 PM CDT Fri Sep 11 2026

Thunderstorms will be the main concern, with the main chances
before 6z and mainly east of the James River, Otherwise strong
southerly winds will turn west and north, then gradually taper
off a bit through the night. Outside of any thunderstorms, VFR
conditions are expected.

&&

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

&&

$$

UPDATE...08
DISCUSSION...AJP
AVIATION...08