308
FXUS63 KDMX 011130
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
530 AM CST Mon Dec 1 2025

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Light snow will move quickly across Iowa today, with around in
  inch of accumulation roughly along the Interstate 80 corridor,
  ranging up to near 3 inches in southeastern Iowa. Winter
  Weather Advisories are in affect in that area.

- Some flurries or a dusting of snow may occur on Wednesday,
  followed by much colder temperatures from Wednesday night
  through Thursday. Low temperatures around sunrise Thursday
  will range from 10 to 15 below zero across much of the area.

&&

.DISCUSSION...
Issued at 256 AM CST Mon Dec 1 2025

A surface high pressure area is draped across Iowa and
neighboring states early this morning, resulting in very light
winds and cool temperatures. Meanwhile, a broad 500 MB trough is
approaching from the High Plains, and the broad lift along and
ahead of this trough is generating layered clouds that are
mitigating overnight cooling and keeping temperatures from
falling too far. As gradual saturating of the column continues
today light snow will eventually be generated, however it will
need to overcome a stout low-level dry layer to reach the
surface. Forecast soundings indicate this dry layer is most
substantial in our northern counties and less so in the far
south, which is also where frontogenetical forcing is more
robust. As a result, accumulating snow is more likely in the
south/southeast, and have maintained high (70-100%) POPs in that
area while trending down and including more flurries in the
north/northwest. With the forcing being modest and moving
through quite quickly today QPF is low, only around 0.1-0.2" in
near the Missouri border. However, forecast soundings indicate
several hours with a deep dendritic growth layer below the
frontogenetical forcing (which is more toward 600-700 MB), so
snow-to-liquid ratios should be fairly high. In other words,
while the liquid equivalent precipitation is unimpressive, the
snow will be dry and fluffy and accumulate to a bit greater
depth than normally anticipated for the QPF. Have maintained
SLRs around 18:1 or so and still expect snowfall amounts from
around an inch in central Iowa to 2-3 inches in the far
south/southeast. Given these relatively low amounts and the
expected character of the snow impacts should not be great,
however, they may be enhanced by the snow coming on top of
remaining snow from the bigger system a couple days ago, and
with this being the first work/school day for many after the
holiday, the ongoing Advisory is prudent and has been maintained
without adjustment. We will be monitoring radar and
observational trends today in case forecast snowfall amounts or
the Advisory area/timing need to be updated.

Today`s shot of light snow will move quickly out around this
evening as the 500 MB trough axis moves overhead, yielding to a
quieter pattern from tonight through Tuesday. On Tuesday night
another broad 500 MB trough will approach from the northwest,
while at the surface a large Arctic high pressure area surges
southeastward from southern Canada into the Dakotas. The leading
push of this high pressure area will form an effective low-
level cool front over South Dakota/Minnesota early Tuesday
night, which will subsequently push through Iowa around
Wednesday morning. The low-level convergence in this effective
frontal zone, beneath broad but modest forcing for ascent
associated with the approaching 500 MB trough, will generate
clouds and light snow late Tuesday night and Wednesday as the
system moves through our forecast area. However, moisture will
be very limited and forecast soundings do not give much
indication beyond flurries or perhaps a light dusting of snow.
Some solutions, such as the NAM, do increase frontogenetical
forcing along the boundary as it reaches southeastern Iowa
Wednesday afternoon, which could result in a quick shot of
lightly accumulating snowfall. However, with most models
indicating little to no accumulation have maintained lower POPs
(20-30%) with no amounts advertised. POPs may need to be raised
in subsequent updates, even if amounts do not increase, as it
does appear somewhat more likely that flakes will fly even if
they do not accumulate.

On Wednesday night and Thursday the large high pressure area
will settle right over Iowa, bringing very cold temperatures.
The current forecast calls for low temperatures Thursday morning
around 10 to 15 below zero across much of our area, with
apparent (or "feels like") temperatures approaching 15 below in
the south to 20 or 25 below in the north around sunrise.
However, winds will be light during this time which will
mitigate impacts somewhat. Still, it will be quite a slap in the
face this early in the season, and even during the day it will
not be much better as forecast highs Thursday afternoon are only
in the single digits to lower teens above zero. Bundle up folks.

After the cold high pressure area moves quickly away Thursday
night we will see some moderation of temperatures, however, the
500 MB pattern becomes more active with multiple shortwave
troughs moving over the region at the end of the week and next
weekend. Resolving the details of these systems is ambiguous at
this time, but some additional chances for snowfall may ensue.
Something to keep an eye on as this week progresses.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 530 AM CST Mon Dec 1 2025

Very low ceilings, and some -SN and BR, are currently affecting
the area with IFR or LIFR conditions being reported at all
terminals. Ceiling heights range from FL003-FL008 and will be
slow to rise later this morning, but should reach MVFR around
FL012-016 during the afternoon. Meanwhile, snow is moving in and
will primarily impact DSM and OTM from later this morning
through the afternoon, with visibility falling below 3SM at
times and possibly below 1SM for brief periods especially at
OTM. Have indicated these trends in the 12Z TAFs, but amendments
are likely today. Even after the snow moves out this evening,
reduced ceilings and visibility in BR may linger through the
remainder of the TAF period.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...

Winter Weather Advisory from 9 AM this morning to 9 PM CST
this evening for IAZ074-075-084>086-095>097.

Winter Weather Advisory until 6 PM CST this evening for IAZ083-
092>094.

&&

$$

DISCUSSION...Lee
AVIATION...Lee