388
FXUS63 KDMX 111742
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1142 AM CST Thu Dec 11 2025

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Band of snow passes over northwest into central and
  southeastern Iowa today into this evening with accumulation of
  1-3 inches possible. On the southwest side over portions of
  western and southern Iowa, light ice accumulations are
  possible.

- Accumulating snow Saturday with very cold air Saturday into
  Sunday. Cold weather headlines look increasingly likely early
  Sunday.

- Moderating temperatures and trending dry early next week.

&&

.UPDATE...
Issued at 1042 AM CST Thu Dec 11 2025

A few notable trends this morning have led to a change in the Winter
Weather Advisory. Profiles are notably colder compared to output
yesterday, that max wet bulb aloft remaining below freezing where
the QPF axis will be. This means that there is a decrease in
freezing rain, and a slight increase in snow. Strong isentropic
ascent on the 295K surface (approaching 50kts) pack the moisture
along a tight fgen band angled on a NW to SE diagonal. The fgen will
be the primary source of forcing and will lead to a tight moisture
gradient on the southwest side of the snowfall axis.

Looking at cross sections, as the fgen band ascends towards the DGZ,
omega eclipses -20 microbars. The peak lift occurs just below the
DGZ, favoring sub-climo SLRs. This is because snow formation will
favor plates over dendrites. That being said, the DGZ just aloft
will benefit from convective processes and thus an added boost to
snowfall rates, evidenced by spreading/folding of the theta-e
surfaces in cross sections. The snowfall rates peak in the mid
afternoon, geographically Des Moines. So the highest rates will
affect the beginning of rush hour. Given the southwest shift as
well as the travel sensitivities in the populated portions of
central Iowa, have expanded the Winter Weather Advisory
southwest by a county length. Trimming of the northeast flank is
possible this afternoon, which will be evaluated in the full
forecast package.

&&

.DISCUSSION...
Issued at 242 AM CST Thu Dec 11 2025

High pressure across the area tonight has kept things quiet and
allowed for breaks in the cloud cover. Pull up GOES-east water vapor
imagery and look of to the west and see our next approaching system
reaching South Dakota early this morning. Precipitation will reach
northwest Iowa late morning and expand to central and southeast Iowa
through midday. This diagonal band bisecting the state from NW to SE
will produce a band of accumulating precipitation across the area
this afternoon into this evening. Most of the precipitation in the
band is expected to fall as snow with soundings showing deep
saturation through the dendritic growth zone paired with moderate
lift in this deformation zone. As the event progresses, the area of
best lift will shift lower in the atmosphere below the DGZ,
resulting in lower accumulation rates. Meanwhile, warm air advection
will be pushing into the state out of the southwest and into central
Iowa. This will result in a warm layer aloft. Models have trended
colder in the 00z and 06z runs, with less ice accumulation than
previous runs as the warm nose aloft does not quite exceed 0z
(or at least, not for as long or over as deep a layer). Have
trimmed down the ice accumulations to reflect recent trends,
however it is important to note that the potential for ice
accumulation has not gone away completely and event minor ice
can result in hazardous driving conditions. As the evening
update aptly noted, afternoon insolation should help to mitigate
slick spots early in the afternoon, however late afternoon and
through the evening conditions will likely worsen as the sun
goes down. Slack spots will likely make for hazardous travel
during the evening commute. As the event tapers off late
tonight, the HRRR has noted a brief period with lack of ice
introduction resulting in freezing drizzle. This should be
short lived and light, but would add to any earlier ice
accumulations. It is also worth noting that the synoptics
(GFS/Euro) have been further south with the band bisecting the
state practically corner to corner from NW to SE, the CAMs favor
a solution further northeast. With placement still uncertain,
have issued a winter weather advisory for areas expecting to see
2-3 inches of snow. These are marginal totals for an advisory,
but the the possibility of a wintry mix including ice
accumulation and the event occurring through the evening
commute, felt it would best convey potential impacts.
Adjustments may yet be needed if the band shifts or if higher
ice accumulations look possible.

There will be a lull in activity on Friday before the next wave in
this wave train in arrives on Saturday. As a fellow forecaster
noted, this should be the caboose in the wave train as the
following several days look to remain dry and warming back
towards seasonal temperatures for this time of year. Before
that, the Saturday system. This embedded shortwave passes
quickly across the area on Saturday the the deformation zone
passing over Iowa. Conditions are cold enough that snow is the
only precipitation type with 1-3 inches expected through the
day. Cold air pushes into the area on Saturday with morning lows
from the single digits above zero south to below zero north
(and wind chill from 0 south to -20 north). Reinforcing cold
air follows the Saturday snow and overnight lows thorugh Sunday
morning will be well below zero. Sunday morning wind chills
will be in the the -20 to -30s across most of Iowa. Cold
Weather Advisories and Extreme Cold Warnings are expected this
weekend. Dry conditions settle in Sunday through at least the
first half of next week with temperatures moderating back into
the 30s to low 40s.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1136 AM CST Thu Dec 11 2025

Main change has been a southwestward shift in the snow band and
a downtrend in ice potential. So changed the prevailing weather
groups to -SN and removed FZRA. That being said, some FZRA could
mix in, but accumulations will be minimal.

Added a Prob30 group for 1/2sm vsbys because snowfall rates
will likely peak near the terminal in the Prob30 window. The
uncertainty comes from how narrow the band will be, which at
issuance time looks to just miss the terminal to the northeast.
Will AMD to TEMPO if upstream obs warrant. Similar adjustments
have been made to KOTM, but with 1SM.

IFR cigs will linger for much of the rest of the period.
Easterly winds will shift to northwesterly through the night.
Some freezing drizzle possible at 12z, but not enough factors
supporting it to add to the TAF at this time.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until midnight CST tonight for
IAZ004>006-015>017-023>027-033>039-046>050-060>062-074-075-086.

&&

$$

UPDATE...Jimenez
DISCUSSION...Hagenhoff
AVIATION...Hagenhoff/Jimenez