543
FXUS63 KFSD 021738
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1238 PM CDT Tue Sep 2 2025

.KEY MESSAGES...

- Dense Fog Advisory has been cancelled as conditions have
  improved over the area. Patchy fog with visibility below one
  half mile may occur through 11 AM CDT.

- After a few spotty showers this morning mainly across
  southwestern MN, more widespread showers and thunderstorms
  chances (30%-60%) return from the late afternoon into
  overnight hours. An isolated severe risk will be possible
  between 5pm to 11pm with quarter size hail and 60 mph wind
  gusts being the primary threats.

- More Canadian Wildfire smoke will return to the region by
  Wednesday. While the highest concentration should stay aloft,
  brief reductions to surface air quality and visibilities will
  be possible.

- Fall-like temperatures will return from the midweek into the
  weekend as an unseasonably strong system brings much cooler
  air to the northern plains/upper midwest.

&&

.DISCUSSION...
Issued at 632 AM CDT Tue Sep 2 2025

TODAY & TONIGHT: A slightly warmer day ahead. Taking a look across
the area, its another rinse and repeat with patchy areas of fog
continues to develop mostly along the Missouri River Valley. While
we could see a gradual expansion of the fog into portion of
northwestern IA, current thinking is patchy cirrus aloft will do
just enough to keep things from becoming more widespread. With this
in mind, likely going to hold off on an advisory for now though
locally dense patches could lead to visibilities of a mile or less
at times. Nonetheless, should see conditions gradually improve just
after daybreak as the fog dissipated by mid-morning (9am to 10am).
From here, could see a few isolated showers move into portion of
southwestern MN this morning as another mid-level wave progresses
into central MN. However, this activity should gradually weaken with
southeastward extent as the nocturnal LLJ weakens. Otherwise, expect
slightly warmer conditions as southwesterly surface winds and
increasing mid-level warm air advection (WAA) leads to temperatures
in the upper 70s to low 80s for the day with the warmest conditions
west of the James River Valley.

Shifting gears to our precipitation chances, a cold front will slide
southeastwards this evening with a strong mid to upper-level wave
behind it. Looking at the CAMs, most of the 02.06z run have this
near-surface feature reaching our northwestern-most zones around 22z
(5pm) with convection developing along/ahead of the front. Given the
1000-2000 J/kg of instability and 35 kts of bulk shear, there should
be just enough there for an isolated severe risk with the strongest
activity being capable of producing up to quarter size hail and 60
mph winds though the better sheer is offset from the better
instability. While the probabilities are low, can`t completely rule
out an isolated tornado either especially if something gets anchored
to the front given the low LCL heights. Nonetheless, as the activity
continues to progress southeastwards with the front; should see most
of this activity gradually weaken as the instability wanes with the
loss of diurnal heating somewhere between 10pm to 11pm. From here,
an additional round of scattered scattered showers will likely
progress southeastwards out of ND with previously mentioned wave.
Though more widespread in coverage, the atmosphere should be worked
over enough for the convective risk to be low but non-zero heading
into Wednesday.

WEDNESDAY-FRIDAY: Looking into the middle to latter parts of the
week, an active pattern continues aloft as an upper-level low (ULL)
traverses the international border into the northern plains and
Great Lakes Regions by Wednesday. With pieces of energy rotating
around the main low, expect the scattered showers to continue
through the first half of Wednesday. However, with only a couple
hundred jules (100-300 J) of instability to work with and plenty of
shear (35-45 kts); can`t completely rule out an occasional rumble of
thunder with this developing activity. However, the main benefit
will be some decent rainfall with accumulations of 0.10" to 0.30" of
an inch possible. From here, expect cloud cover to gradually
decrease from northwest to southeast as another plume of Canadian
Wildfire smoke move through the area. While the highest
concentrations are expected to stay aloft, reductions in surface air
quality ad visibility will be possible for most of the day on
Wednesday. If you`re apart of a sensitive group and/or have any
outdoor plans, make sure to monitor your local air quality for
updates.

Shifting gears here, quieter conditions should return by
Thursday as a surface ridge moves through the plains. Could see some
additional rain chances (20%-30%) mainly east of I-29 by late
Thursday as a clipper wave rotates around a now established Hudson
Bay Low. However, with limited moisture in sounding profiles; expect
any accumulations to be limited at best. Looking into Friday,
quieter conditions should once again return as building upper-level
ridging over the western CONUS pushes the Hudson Bay Low eastwards.
Lastly, fall-like conditions will return by Wednesday as colder air
filters into the region behind the previously mentioned cold front.
With temperatures expected to hover around 4 to 8 degrees C at 850
mb over the next couple of days (lowest 1 to 2.5 percentile of
climatology), expect our temperatures to reflect that with highs
mainly in the 60s to 70s and overnight lows in the upper 30s to low
40s for most areas. With this in mind, we`ll have to continue to
monitor the temperatures by Wednesday night as some areas could
receive their first frost of the season.

SATURDAY ONWARDS: Heading into the extended period, mid-level
ridging move into the Plains by Saturday bringing a boost of mid-
level warm air advection (WAA). This along with a return to
southerly to southeasterly flow will help temperatures gradually
climb towards the 70s for highs on both Saturday and Sunday. Could
see some rain chances begin to build back into the region from
Sunday night into Monday. However, long-range guidance hasn`t
narrowed down the finer details as of yet so its a bit uncertain at
this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1224 PM CDT Tue Sep 2 2025

A few concerns through the TAF period. Rain showers and isolated
lightning continues across southwestern MN through the early
afternoon hours, near/north of KMML and KTKC.

Next focus is the cold front moving through the region this
evening and into tonight. Scattered showers and storms are
expected to fire near the front. Expect the front near KHON
around 02.22-03.00z, KFSD between 03.01-03z, and KSUX around
09z. Have included a PROB30 mention at KHON and KFSD, but
omitted from KSUX as activity looks to stay to the east of the
airspace. Showers/storms could lead to MVFR conditions.

Showers and isolated storms develop behind the front, with the
heaviest focused for the James and MO River Valleys. Again,
could see MVFR/IFR conditions with this activity but too low
confidence on the timing to include. Showers should exit from
north to south through the late morning hours, lingering into
the afternoon along the MO River.

Finally, wildfire smoke aloft and at the surface move in behind
the front, leading to reduced visibility. Northwesterly winds
toward the end of the period will gust to around 25 knots.

&&

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

&&

$$

DISCUSSION...05
AVIATION...SG