041
FXUS63 KDMX 020809
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
209 AM CST Tue Dec 2 2025

.KEY MESSAGES...

- Freezing fog this morning, mainly north and west. The fog may
  be dense at times.

- Flurries or a dusting of light snow late tonight into
  Wednesday, then much colder temperatures late Wednesday
  through Thursday. Lows well below zero Thursday morning,
  possibly -15 or below in a few locations.

- More active weather pattern from around the end of the week
  into early next week. Additional snowfall will be possible at
  times, but details are unclear at this range.

&&

.DISCUSSION...
Issued at 209 AM CST Tue Dec 2 2025

A large surface high pressure area centered over the southern
High Plains of Oklahoma and Texas has extended up across Iowa
overnight, providing light southwest winds. A stubborn band of
low stratus clouds remains from Monday`s system and is currently
draped from Wisconsin and eastern Minnesota down across eastern
Iowa and Missouri. However, it is slowly moving eastward as the
Monday system departs in that direction and the aforementioned
ridge builds in from the west. Behind the stratus, over western
and northwestern Iowa, temperatures are falling rapidly over the
fresh snow pack and fog has begun to develop. Most high-
resolution short-term model guidance blows the fog up between
now and sunrise, which is at least to some extent consistent
with recent observational trends. Have expanded wording of
freezing fog this morning, especially across our northern
counties, and will watch closely to see if the fog either
becomes widespread dense, which seems less likely, or actually
deposits ice onto surfaces which may be more of a concern. This
will be the primary forecast problem of the morning, as
otherwise the weather is quiet and will remain so into tonight.

By this evening a broad 500 MB trough will be rounding over
the Dakotas, with a weak accompanying surface trough trailing
from around the Minnesota arrowhead southwestward into South
Dakota. Behind that, a large Arctic high pressure area will be
surging southeastward from southern Canada into the north
central U.S., essentially building in right behind the weak
surface trough. As the trough moves through our forecast area
late tonight and Wednesday morning, the low-level convergence
along it beneath broad but modest forcing for ascent aloft
should generate clouds and light snow. However, forecast
soundings indicate a prevalence of dry air and any notable
frontogenetical forcing is quite transient, so flurries or a
dusting of snow appear to be in store and have maintained low
(20-30%) POPs accordingly with no snow accumulations advertised.
Given the timing of the trough passage, it is likely that
surface winds in our area will remain south southwesterly for
much of tonight with thickening clouds overhead, leading to
steady or even slowly rising temperatures overnight. This will
then come crashing to a halt behind the trough, as the much
colder airmass associated with the Arctic high surges in,
resulting in falling temperatures through the day on Wednesday.
Have accounted for this with non-climatological diurnal
temperature trends in the forecast, and it will be a rude
awakening as the cold air pushes in on Wednesday. The large high
pressure area will then move directly over Iowa late Wednesday
night into Thursday morning, leading to ideal conditions for
radiational cooling on the deep snow pack in place across much
of our service area. This will push Thursday morning lows down
to around 10 below zero or colder over much of our area, and
despite light winds the Wind Chill may scrape 20 below at times,
mainly across the north.

The cold high pressure area will begin to move away to the east
late Thursday, and thereafter a northwesterly 500 MB flow regime
will set up from the end of this week through the weekend and
into early next week. Within this pattern, multiple "clipper
system" impulses will move quickly overhead in rapid succession,
resulting in quickly alternating low-level ridge/trough passages
and multiple opportunities for additional precipitation during
this active period. Temperatures generally support snowfall, and
while the systems will be moving through quickly there will be
multiple opportunities for some snowfall accumulations between
around Friday and next Monday or Tuesday. However, at this range
the details of when, where, and to what depth any such snowfall
may occur are unclear. This will bear watching in the coming
days as travel impacts may occur at times around this weekend
and early next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1043 PM CST Mon Dec 1 2025

A wide stripe of MVFR stratus blankets central Iowa tonight.
This is slowly moving east with expectation of patchy fog
development in areas that clear out. While some dry air in place
may limit more substantial fog development, radiational cooling
in the absence of cloud cover should be enough and a few
locations in Minnesota that have cleared out already tonight
have developed patchy fog. Improvement is expected through
Tuesday as cloud cover and fog diminishes.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

DISCUSSION...Donavon/Lee
AVIATION...Hagenhoff