368
FXUS63 KFSD 081735
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1135 AM CST Mon Dec 8 2025

.KEY MESSAGES...

- Fog continues to expand in coverage this morning. Have
  expanded the Dense Fog Advisory to cover a large portion of
  locations along and north of I-90 and the vast majority of
  northwest Iowa. This new extension of the Advisory is in
  effect until 10 pm this evening. Slick spots are possible on
  roads and untreated surfaces.

- A busy week is ahead with a risk of precipitation nearly every
  1.5 days. Most of the precipitation events this will remain
  light, but systems on Thursday and Friday will bear watching.

- Confidence is high that winds Tuesday night into Wednesday
  may exceed advisory criteria with potential for 55+ mph winds
  in a few areas. We`ll need to monitor the snow pack and air
  temps closely to monitor blowing snow potential.

- Confidence is also moderate that arctic air will bring near
  advisory level wind chills to the region by next weekend.

&&

.UPDATE...
Issued at 1019 AM CST Mon Dec 8 2025

Visibilities have lowered across a large part of the area down to a
half a mile or less in fog. As such, have expanded the Dense Fog
Advisory to include a large portion of areas along and north of I-90
and down through the vast majority of northwest Iowa. With southerly
winds in place, additional low level moisture advection will keep
fog or at least very low stratus in place. Have set the expiration
time for the new extension of the Dense Fog Advisory through 10 pm
this evening. Will continue to monitor trends in the fog and may
need to adjust the Advisory as well. With a few locations reporting
light snow or freezing fog, slick spots are possible on roads
or untreated surfaces.

&&

.DISCUSSION...
Issued at 348 AM CST Mon Dec 8 2025

TODAY & TONIGHT: A slightly more mild day ahead! Taking a look
across the area, any lingering flurries has mostly tapered east of
our area this morning leaving behind low areas of stratus. As we
head towards daybreak this morning, some of these lower clouds could
start to act as fog as lighter winds settle in. While this could
lead to rapid changes in visibility and potentially a few slick
spots this morning, expect the areas of fog to hang around for the
first half of the day before dissipating. With this in mind, make
sure to slow down and drive to the conditions on those morning
commutes! From here, should see temperatures gradually increase as
southerly surface winds and a surface warm front help temperatures
peak in the low 30s to mid 40s for the day with the warmest
conditions west of the James River Valley. Otherwise, another mid-
level wave will pass through parts of the northern plains during the
second half of the day. Nonetheless, with the better dynamics and
saturation north of us, we should stay mostly dry.

TUESDAY-THURSDAY: Looking into the midweek, an active pattern
continues aloft as northwesterly flow helps usher in multiple waves
over the coming days. The first of which will arrive by Tuesday
increasing precipitation chances (30%-60%) for areas mainly along
and north of I-90. However, with mild temperatures in the upper 30s
to upper 40s expected; most of this precipitation should fall as
rain throughout the second half of the day with mainly light
accumulations. While we can`t rule out change over to snow as
temperatures fall by late evening, accumulations (if any) should be
light with most ensemble guidance showing a 40%-60% chance of
accumulations of 0.20" of an inch of snow mainly across southwestern
MN. Besides the precipitation, the main concern with this system
revolves around the stronger winds behind it. As mentioned in the
previous discussion, almost every piece of guidance continues to
show high confidence in advisory (45+ mph) level wind gusts between
Tuesday night and Wednesday. Some guidance even suggests up to 55
mph winds in our higher elevation areas at times. With this in mind,
decided to continue the trend of boosting sustained winds and wind
gusts for this time period (21z Tue-09z Wed).

While a wind headline will likely be needed, decided to hold off on
things for now after collaboration with neighboring offices.
However, we`ll likely continue to message the potential for stronger
winds over the coming days. While there is still some uncertainty,
we`ll also have to monitor the quality of our snowpack over the next
few days as the stronger wind could cause periods of blowing and
drifting snow as temperatures fall overnight. Nonetheless, this will
depend on how crusted over the snow is and if its still blowable.
Shifting gears here, a quick surface high will slide through through
the area by Wednesday as colder air filters in behind the previously
mentioned system. While this will likely kick start our cooling
trend into the weekend, highs will decrease into the teens to upper
20s through Thursday. Lastly, our next concrete chances for snow
likely return between Wednesday night and Thursday as another
clipper wave swings through. While exact amounts are still
uncertain, ensemble guidance does show some moderate confidence (30%-
40%) in at least an inch or greater of fresh snow. With this in
mind, make sure to monitor your local forecast as this would the
period to monitor the most.

THE WEEKEND: Heading into the weekend, temperatures will continue to
trend colder from Friday onwards as colder air filters in behind
another cold front. This will lead to temperatures in the single
digits to teens through at least Saturday. Additional chances for
snow will be possible by Friday. However, uncertainty remains as
long-range guidance diverges in potential solutions. Lastly, be
prepared for even colder wind chills each night through Sunday
morning with values as cold as -25 degrees possible. While the
coldest conditions will likely occur by Friday night, each night
will have the potential for advisory level wind chills at times so
this will be something to monitor moving forward.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1134 AM CST Mon Dec 8 2025

Latest satellite imagery shows low level stratus and fog across the
majority of the area. Ceilings and visibilities range through the
entire set of flight categories from VFR to LIFR. VFR conditions are
present across parts of south central South Dakota with all other
lower categories along and north of I-90 and the entirety of
northwest Iowa. With weak southerly low level winds in place, think
the fog and stratus will persist through the rest of the daylight
hours. Winds then begin to take on a westerly component late this
afternoon and evening. Think that the fog and stratus will begin to
push eastwards and clear all TAF terminals and the entire area as
this westerly component kicks in.

Winds will turn back to out of the south/southwest by tomorrow
morning. The next chance for precipitation looks to return to the
area by the end of the TAF period. This looks to be generally along
and north of highway-14. Precipitation will be in the form of light
freezing rain before transitioning to plain rain. Low level wind
shear (LLWS) is also possible to end the period as well by KHON.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Dense Fog Advisory until 10 PM CST this evening for SDZ038>040-
     052>058-062.
MN...Dense Fog Advisory until 10 PM CST this evening for MNZ071-080-
     081-089-090-097-098.
IA...Dense Fog Advisory until 10 PM CST this evening for IAZ001>003-
     012>014-020>022-032.
NE...None.

&&

$$

UPDATE...Meyers
DISCUSSION...05
AVIATION...Meyers