685
FXUS63 KFSD 011906
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
206 PM CDT Mon Sep 1 2025

.KEY MESSAGES...

- Isolated to scattered showers develop this afternoon and
  evening. A couple of rumbles of thunder are possible. Although
  risk is low, a couple of funnel clouds may occur with
  developing showers. These are not expected to reach the
  ground.

- Fog, including dense fog, is expected again tonight. Be
  prepared for reduced visibility during the morning commute
  Tuesday.

- Isolated showers and storms are possible over southwestern
  Minnesota Tuesday morning into early afternoon. However,
  greater and more widespread showers and storms (30%-60%
  chance) return late Tuesday afternoon and night. A few storms
  during this time along and north of Interstate 90 could become
  severe with quarter sized hail and 60 mph as the main
  threats.

- Fall-like temperatures return mid week into the weekend as an
  unseasonably strong system brings much colder air to the
  northern Plains and Upper Midwest.

&&

.DISCUSSION...
Issued at 202 PM CDT Mon Sep 1 2025

NOW THROUGH TONIGHT: Diurnally driven cumulus has become widespread
over the area, with an upper level wave evident via some cirrus
moving across eastern SD. Isolated to scattered showers and isolated
storms develop through the afternoon and evening (as we`ve seen the
last couple of days). With that, can`t entirely rule out some
isolated funnels as showers develop with the low LCL height and
enhanced stretching potential - especially across southwestern MN
into the US Highway 14 corridor. Not expecting any of these to reach
the ground, but head indoors if you feel your safety is threatened.
Otherwise, highs today in the 70s, coolest by US Highway 20 where
rain lingered this morning and clouds have limited warming thus far.

Light winds over the area tonight should be conducive to fog
development overnight into the daybreak hours Tuesday. Guidance
indicates that there may be areas of visibility of 1/4 mile or less.
Be prepared for reduced visibility for the morning commute.
Temperatures tonight fall into the 50s.

TUESDAY/TUESDAY NIGHT: Any fog which develops should mix out by the
mid morning hours. Shower and isolated storm chances continue
through the day Tuesday and Tuesday night. A mid level wave moving
across the forecast area during the daytime hours with some WAA
should be enough for some isolated activity, mainly across
southwestern MN through early afternoon. Toward the evening hours, a
cold front slides southeast, with a stronger mid/upper wave behind
it. Models vary on the timing of the front still with most guidance
bringing the front into the US Highway 14 corridor by 02.22z (5 PM
CDT) with later models closer to 03.00-01z (7-8 PM CDT).

A couple of strong to severe storms are possible, although greatest
shear is offset in time and space from the highest instability
during the afternoon and evening hours. Still, mid level lapse rates
around 6-6.5 deg C/km, instability around 1500 J/kg, and bulk shear
around 30 knots could be enough for some 60 mph wind gusts and
quarter sized hail. Although risk is low, a tornado can`t be ruled
out given our proximity to the front, low LCL heights, and 0-1 km
shear around 15 knots from some guidance. Brief locally heavy rain
is possible although may be shorter lived given the progressive
nature of the front. Highest risk for severe will be in the late
afternoon and evening hours, although this will depend on the timing
of the front. Area of concern is along and north of I-90.

Southerly surface flow ahead of the cold front along with the
aforementioned WAA will allow temperatures to warm near to above
normal for early September - especially for areas west of the James
River. Highs in the mid 70s (east) to mid 80s (west). Lows tomorrow
night in the 50s with showers and storms continuing to move south
through the area.

MID WEEK: Showers and maybe some isolated storms remain over the
area Wednesday as a short wave moves through on the heels of the
cold front and we see the nose of an upper jet streak rotate around
the upper low near the International Border and UP of MI. Although
we`ll remain under the influence of this jet and upper level low on
Thursday, surface high pressure to our southwest may limit rain
chances to east of I-29 later in the evening and night with another
front moving through.

CAA with northwesterly flow through most of the atmosphere
leads to cooler conditions Wednesday, with temperatures below normal
for the start of meteorological fall. Breezy conditions anticipated
Wednesday, with wind gusts around 25 to 30 mph. Temperatures may
moderate somewhat with some weak WAA Thursday, but northwesterly
flow and cloud cover thanks to the strong upper level low to our
east should temper warming potential. Highs in the 60s Wednesday and
mid 60s to upper 70s Thursday. Lows mid week in the 40s.

FRIDAY-THE WEEKEND: The upper level low moves east through Friday,
with mid/upper level ridging building across the western CONUS. This
moves east through the weekend, breaking down as it does so.
Guidance diverges quite a bit as we head through Saturday night
regarding where and when any waves move through the pattern.
Generally expect surface high pressure prevails, so expect mostly
dry conditions. Temperatures remain below to near average with highs
in the mid 60s and 70s and lows in the 40s.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1219 PM CDT Mon Sep 1 2025

Diurnally driven cumulus clouds have expanded over the area the
last hour or so, leading to a mix of VFR/MVFR ceilings. Isolated
to scattered showers are expected as well, along with an
isolated rumble of thunder. Given the placement of the activity
near KSUX, added a VCSH mention for a few hours this afternoon.
For KFSD, maintained the PROB30 for the -SHRA based on latest
hi-res guidance trends.

Light winds tonight should allow fog to redevelop late tonight
into Tuesday morning. Have added some MVFR mention to KFSD and
KSUX, but could see some IFR and lower visibility. Will wait to
mention anything lower until timing/coverage details become
more clear.

Isolated showers possible tomorrow morning across southwestern
MN, with better and more widespread rain chances tomorrow
evening after this forecast period ends.

&&

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

&&

$$

DISCUSSION...SG
AVIATION...SG