337
FXUS63 KFSD 232030
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
230 PM CST Sun Nov 23 2025

.KEY MESSAGES...

- Another round of fog is expected overnight tonight through
  Monday morning, particularly over the James River Valley east
  through southwestern Minnesota and northwestern Iowa.

- Light rain is possible (40-60% chance) on Monday for locations
  southeast of a line from Tyndall, South Dakota to Jackson,
  Minnesota. Accumulations are expected to be less than two
  tenths of an inch.

- Much colder temperatures will move into the region on Tuesday,
  leading to temperatures being 10 degrees below normal through
  next weekend. This cold air will also switch the light rain to
  light snow for areas north of I-90. At this time, little to no
  snowfall accumulation is expected.

- Winds Tuesday will be out of the northwest gusting 25 to 35
  mph over far northeastern Nebraska, southwestern Minnesota,
  and northwestern Iowa. The strongest winds, gusting 35 to
  around 45 mph will be west of the James River. The
  combination of little to no precipitation and strong winds may
  result in high Grassland Fire Danger Index values over
  portions of south central South Dakota on Tuesday (mainly
  Gregory County).

&&

.DISCUSSION...
Issued at 230 PM CST Sun Nov 23 2025

The main highlight in the short term will be a storm system tracking
across the region early next week which will bring chances of rain
Monday, mainly from northeastern NE through southwestern MN,
covering portions of southeastern SD and northwestern IA. Patchy to
areas of fog is possible once again late tonight into Monday
morning, mainly for locations along the James River and over the
Coteau. Patchy to areas of fog is also possible over portions of
southeastern SD into southwestern MN and into IA/NE. How dense it
could become is low confidence with some of the lower viz due to the
rain. Probability of visibility at or below 1/4th mile (HREF
ensemble)ranges from 50-65% along and east of a line from Brookings
to Sioux City. I was a bit hesitant to issue a fog advisory this far
out in time, so will pass it along to the next shift to determine if
one is needed closer to time.

By 00Z Monday, models agree on split flow aloft with a broad low
amplitude ridge stretching across the northern half of the CONUS
with an embedded shortwave, and its weak surface low, over southern
Manitoba. The southern stream consists of a nearly stacked 500mb
closed low to surface over Colorado. Through 12Z Monday, the ~1009mb
Colorado low will track into western Kansas with models overall
agreeing on this location, with GEFS just a touch northwest than the
other models. Through the afternoon, this Colorado Low will then
track southeast (as its closed low turns back into an open wave)
with models overall agreeing on the center of the low along the
KS/OK border by 18Z (and its now open shortwave trailing shortly
behind). At the same time, a shortwave will move in off the Pacific
and over the Pacific Northwest with its broad area of low pressure
setting up over northeastern WY and northwestward into MT.

With the track of the Colorado Low, both GEFS/ENS and short term
ensembles agree on portions of the region getting clipped by the
northern edge of this low with precipitation, in the form of rain,
however there is a spread in exact QPF amounts and how far north the
precip could extend. As of now, rain is forecast to move in early
Monday morning over northeastern NE and spread northeast through
southern MN through the afternoon. HRRR keeps the precip more south
and mainly tracking over NE into IA and barely clipping far
southeastern SD into MN while HiRes ARW is more aggressive on a
northward trend. Latest NBM does a decent job with its pops, with
the highest chances (40-65%) along and southeast of a line from
Tyndall, SD to Jackson, MN with the highest pops over northeastern
NE through northwestern IA. QPF amounts generally in this higher
pops area of NE/IA could range between 0.10-0.25" Monday into Monday
afternoon.

Monday night through next weekend...

Primary focus of the long term part of the forecast will be the
transition from Fall to Winter on Tuesday, which will remain through
the start of December. The transition will be driven by a strong
shortwave over the Pacific that will move into the PacNW tonight and
then quickly move east into the northern Plains Monday night and
depart Tuesday evening. Expect this shortwave and associated weak
surface low (around 1009mb) to bring an initial push of light rain
to northern SD on Monday night (generally north of US-14, but may be
some lingering rain in southwest MN from tomorrow`s precip). Then as
the low moves east Tuesday and intensifies over eastern MN and
western WI during the afternoon, it will wrap in much colder air on
Tuesday morning, switching the rain to snow from northwest to
southeast and eventually putting the eastern SD and southwest MN
(largely north of I-90) in wrap around snow into the evening. The
combination of the snow, with strong N-NWrly winds, may lead to some
travel impacts along/north of US-14/81 on Tuesday.

First for the winds. The initial surge of cold air advection behind
the front will lead to the strongest winds over central and
especially south central SD on Tuesday, where 0.5km winds are in the
35-45kt range. Thus, expect gusts easily in the advisory range for
areas along and especially west of the Missouri River on Tuesday.
Wouldn`t be surprised to see some High Wind Warning gusts for
Gregory and maybe Brule/Charles Mix counties, which is supported by
the NBM 24hr wind gust probabilities of 55mph or greater being over
60-80%. Farther east to the James River Valley, think that area
should see some gusts to advisory level (NBM has 24hr probs on
Tuesday around 70%) and they too may eventually need an advisory.
That matches up with the EC-EFI data highlighting much of SD, except
the northeast, with 0.7-0.8 values, which traditionally lines up
with advisory winds for our region. Will need to watch the
tightening pressure gradient Tuesday aftn/evening near the MN/SD
border areas, as the surface low strengthens. This could lead to an
enhanced 6hr period of winds with gusts reaching advisory level.

The strong winds and dry fuels will lead to elevated fire weather
concerns for locations that don`t experience precipitation on
Tuesday. That looks to primarily be in south central SD, so despite
RH values being up towards 60%, the strength of the winds may
support the need for a Red Flag Watch/Warning, or at least enhanced
messaging in wind products and social media.

Finally, some additional details on the snow side of the forecast. As
mentioned previously, expect to see a steady transition from rain to
snow from northwest to southeast on Tuesday afternoon, as the cold
air surges into the area. At the present time, ensembles have a
decent cluster that have QPF amounts of 0.15" or less along US-14,
but there are members that show amounts up towards 0.25-0.4". This
appears to be tied to the members that have a farther south shift
with the snow. So will need to watch that for any potential
southward trends over the next 24 hours. That being said, the
current probabilities of 1" of snow or more along US-14 is around
20% and then increases as you head north towards Watertown and US-
212. Thus, expect the overall impacts from the snow to be limited at
this time.

For the rest of the week...

A high moves in on Wednesday and remains into Thursday. Could be
some light precip moving into western SD later Thursday and sliding
southeast with time into Friday, associated with an shortwave
dropping southeast through the northwest flow aloft (and mid level
WAA). Still some uncertainty in the ensembles on the location and
amounts, but in general, seems like snow accumulations will be light
(NBM 24hr probs of 1 inch or greater is 50-70%). Beyond that,
uncertainty remains into the weekend, as an upper trough deepens
over the southwest CONUS this weekend and remains in the first part
of next week. Ensembles are consistent on the upper trough being
present, but differ on the location of the trough axis and how
amplified it will be. That being said, with the baroclinic zone
setup to the southwest of our area, stretching from western MT
through southwest SD and into central NE, we`ll still have the
potential for periods of light snow this weekend (30% chance). In
addition, high temperatures will be 10-15 degrees below normal and
in the 20s.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1140 AM CST Sun Nov 23 2025

VFR conditions are forecast to prevail through this evening as
fog is forecast to develop over the region late tonight through
Monday morning, particularly over the James River Valley east
through southwestern Minnesota and northwestern Iowa. Drop in
cigs to IFR to possibly LIFR is forecast at this time for areas
that could receive fog.

&&

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

&&

$$

DISCUSSION...MMM/SRF
AVIATION...MMM