553
FXUS63 KFSD 011135
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
635 AM CDT Mon Sep 1 2025

.KEY MESSAGES...

- Developing areas of fog will persist through mid-morning
  mainly along and north of I-90. With visibilities of a mile or
  less possible through mid-morning, make sure to drive with care.

- Scattered showers will continue through the late morning
  mainly across portions of the lower Missouri River Valley and
  northwestern IA. Additional accumulations of a 0.10" to 0.25"
  of an inch are expected with isolated higher amounts along the
  Highway-20 corridor.

- More showers and thunderstorms chances (30%-50%) will return
  by Tuesday. A few storms could become severe with quarter
  sized hail and 60 mph winds being the main threats.

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

&&

.DISCUSSION...
Issued at 334 AM CDT Mon Sep 1 2025

TODAY & TONIGHT: Another warm and dreary day ahead. Taking a look
across the area this morning, the main focuses continue to be on the
developing areas of fog and scattered showers. Starting with the
fog, lingering low-level moisture coupled with lighter surface winds
has lead to the development of some patchy areas of locally dense
fog mainly north of I-90. While things are mostly spotty currently,
the expectation is for the areas of fog to become more widespread as
temperatures continue to decrease this morning. With all this in
mind, have decided to forgo a dense fog advisory at this time; but
will continue to monitor the trends throughout the morning just
incase a short-fuse advisory is needed. Moving on to the rain, we`re
continuing to monitor an area of light to moderate showers situated
south of the highway-20 corridor this morning. While the rainfall
rates within this area of activity could increase temporarily as a
strengthening nocturnal LLJ interacts with the surface low over
eastern NE, should see most of this activity begin to lose steam by
mid to late morning as the better lift progresses southeastwards.

Nonetheless, quick accumulations of a 0.10" to 0.25" of an inch are
expected across portion of the lower Missouri River Valley with
isolated higher amounts possible along the highway-20 corridor. From
here, expect the dreary conditions to persist for most of the day as
temperatures peak in the low to mid 70s. Could see some spotty
redevelopment east of I-29 as another weak wave progresses through
the area this evening. However, not expecting much organized
development given the limited shear available. Nonetheless, with
this activity being mostly diurnally driven; should see most this
activity weaken by late evening. Lastly, lingering low-level
moisture and lighter surface winds will make a conducive environment
for additional areas of fog tonight. However, the area of focus will
be across the Missouri River Valley and northwestern IA this time.

TUESDAY-THURSDAY: More seasonable conditions will temporarily return
by Tuesday as a combination of southwesterly surface winds and weak
warm air advection aloft (WAA) leads to temperatures in the upper
70s and low 80s across most of the area. More shower and
thunderstorm chances (30%-50%) will likely return from the afternoon
onwards as a cold front swings through the area. While the severe
weather risk is low, can`t completely rule out an isolated stronger
storm or two given the long-skinny CAPE profiles (1000-1500 J/kg)
and 25-35 kts of bulk shear. Given the semi-discrete to cluster
storm modes, marginally large hail (nickel to quarter size) and up
to 60 mph wind gusts will be the primary threats with any stronger
activity that develops. However, the window for any stronger
activity will be fairly small (6pm to 12am) given the limited
instability and will be conditionally dependent on if things can
line up just right on the front. As instability wanes with the
loss of diurnal heating, should see any lingering activity
gradually weaken by late evening as the front progresses
southeastwards.

Looking into Wednesday and Thursday, fall-like conditions will
return as a strong push of cold 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 (lowest 1 to 2.5 percentile
of climatology), expect our temperatures to dip well below our
seasonal normals on both days with highs peaking in the 60s and low
70s. Looking aloft, as an upper-level low (ULL) traverses the
international border into the northern plains and Great Lakes
Regions; expect some spotty showers to persist across the area
through the first half of Wednesday. From here, expect cloud cover
to gradually decrease as surface ridging moves in from the northwest
and breezier conditions set in. Lastly, should see quieter
conditions temporarily return by Thursday along westerly surface
winds.

THE WEEKEND: Heading into the extended period, an active pattern
continue aloft over the Great Lakes Region as another clipper wave
rotates around the previously mentioned ULL. While this could lead
to some additional spotty showers mainly east of I-29 from Thursday
night into Friday morning, not expecting anything remotely organized
given the limited instability and convective temperatures.
Nonetheless, can`t completely rule out some light accumulations
especially across southwestern MN. From here, expect quieter and
cooler conditions for the rest of the weekend as the ULL is pushed
eastwards by a building upper-level ridge. With an influx of weak
mid-level warm air advection (WAA) from the previously mentioned
ridging, expect our temperatures to gradually increase towards our
seasonal normals by Sunday.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 620 AM CDT Mon Sep 1 2025

Taking a look at satellite imagery, scattered showers continue
to move into areas along and south of highway-20 this morning
while areas north of the previously mentioned area are dealing
with patchy areas of MVFR to LIFR fog. As we continue into the
morning hours, expect the fog to gradually erode as peak heating
returns shortly after daybreak. As for the rain, should see the
light to moderate showers continue through late morning before
gradually dissipating. Otherwise, light and variable winds this
morning will become light southeasterly winds this afternoon
then become lighter again overnight to end the TAF period.

&&

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

&&

$$

DISCUSSION...05
AVIATION...05