871 
FXUS63 KFSD 112349
AFDFSD

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

.KEY MESSAGES...

- Strong southerly winds are gusting 30-40 mph with occasional
  gusts to 45 mph along the Buffalo Ridge in southwest 
  Minnesota. Strong winds will decrease through the evening, but
  remain gusty as a cold front moves through the region. 

- A conditional chance for strong to severe storms is expected
  this afternoon and evening mainly east of I-29. While all
  hazards remain possible, golf ball sized hail and damaging 
  winds up to 70 mph will be the primary threats.

- 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.

&&

.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...Wind Advisory until 7 PM CDT this evening for MNZ071-072-080-
     081-089-090-097.
IA...None.
NE...None.

&&

$$

DISCUSSION...AJP
AVIATION...08