181
FXUS63 KDMX 082053
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
253 PM CST Mon Dec 8 2025

.KEY MESSAGES...

- Possible blizzard conditions developing Tuesday night into
  Wednesday morning as strong, gusty winds of 40 to 55+ mph
  unlock existing snow pack. Narrow snow bands are also possible
  after midnight Wednesday into Wednesday morning.

- Before Tuesday night, there is an area of fog moving through northern
  Iowa into tonight. Conditions will be milder on Tuesday as
  well with light wintry precipitation far northern and
  northeastern Iowa with any accumulations minimal.

- Active pattern continues through the rest of the week with additional
  snow chances and colder air returning.

&&

.DISCUSSION...
Issued at 253 PM CST Mon Dec 8 2025

An active weather pattern continues into this second week of
December as northwesterly flow aloft prevails and allows for a
series of shortwave troughs (aka clippers) to track through the
region. Before we get to the clippers and their associated weather,
GOES-East Day Cloud Phase Distinction RGB shows plenty of clouds
over northern and western Iowa with a few peeks at the snow pack
over southeastern Iowa. In addition, an area of fog has been
lingering over northwest Iowa with the Iowa DOT webcam at
Estherville showing a foggy scene. This fog will slowly move
eastward this afternoon into tonight largely north of Highway 30.
Will have to monitor trends into this evening if visibility declines
below a quarter mile, but so far much of today has been a 1/2 mile
at worst in Estherville, but generally above a mile.

As we move into Tuesday, one clipper will be passing into the
western Great Lakes with the next robust clipper moving into North
Dakota Tuesday morning. Between these, strong low level warm air
advection will set up and bring milder air into Iowa. However, cloud
cover will be stout, especially over northern into central Iowa, and
with the snow cover over the state, the initial National Blend of
Models (NBM) is overdone with its degree of mixing and thus warming.
So, have shrunk the diurnal temperature range and am now closer to
the dewpoint temperature, which cuts highs by 3 to 4 degrees. As the
robust clipper approaches from the northwest, its strong forcing
will move over northern and eastern Iowa in the afternoon and
evening. While low level temperatures will be warm enough for rain,
near surface temperatures could be close to or just below freezing.
This may result in a short period of freezing rain over the far
northern and northeastern counties, which transitions to rain as the
warmer air and diabatic processes win out. Any icing looks to be
minimal and relegated to elevated surfaces. With the clipper racing
off to the east, the rain may switch briefly to and end as a bit of
light snow with accumulations similarly minimal.

The big story will be the strong winds that crank up as a cold front
slams through the state Tuesday night with the potential for ground
blizzard conditions developing. There look to be two waves of cold
air advection with the first arriving in the evening. BUFKIT
soundings from the NAM and RAP show impressive winds at 850mb
topping 55 knots for 6 or more hours dropping over much of the
state. As the profile cools, deep, mechanical mixing will begin to
tap into these stronger winds so wind speeds were adjusted upward
with a blend of WRF-ARW and NBM 90th percentile. This pushes gusts
up to around 50 knots/58 mph and high wind warning criteria over
northern Iowa to as far south as Highway 30. However, it is December
and there is a snow pack on the ground, which raises the question of
blowing snow and ground blizzard. The Waterloo snow observer and
here at our office in Johnston both have a blowable snow pack on the
ground at this hour. Temperatures into Tuesday are likely to rise
above freezing, creating a crust on the snow. However, the crust is
likely to be thin and breakable given the prolonged strong wind
speeds forecast Tuesday night. We`ve seen past events where this has
occurred, including the February 7, 2016 blizzard that had higher
temperatures and a deeper crust than this event will have. So, as
temperatures cool and the winds blow, this snow pack will be
released resulting in significant blowing and drifting snow and
visibility reductions. This has resulted in the issuance of a Winter
Storm Watch for (ground) blizzard conditions. As another round of
cold air advection coupled with a trailing strong pressure rise
drops in towards sunrise Wednesday with an elevated front, this
should keep the blowing snow going into the daytime hours waning
towards Wednesday afternoon. As if this all was not enough, the
second push of cold air also steepens low level lapse rates
resulting in low level instability with saturation reaching into the
dendritic growth zone (DGZ). Snow squall parameter, especially based
off of the 1km layer version, are pinging with this boundary from
around a little after midnight over northern Iowa to early to mid-
morning over southern Iowa. Any falling snow will add to the blowing
snow and visibility reductions. Bottom line is that blowing
snow is likely to have an large impact late Tuesday night into
Wednesday morning, especially over northern Iowa, and impacts to
travel in the form of slick roads and reduced visibility are
increasing.

The active pattern continues through the end of the week with
additional clippers and snow chances with temperatures colder
Wednesday and Thursday lower compared to Tuesday. Even colder air
may arrive by late this week into this weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1122 AM CST Mon Dec 8 2025

For northern Iowa (FOD, MCW, ALO), widespread stratus clouds
with MVFR and spotty high end IFR ceilings are prevailing at
midday and should through much of the period. In addition, an
area of fog is forecast to move eastward this afternoon into
tonight with IFR visibility restrictions likely and cannot rule
out a short period of LIFR. Farther south at DSM, VFR
conditions are forecast to return late this afternoon with
mainly VFR prevailing at OTM.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from late Tuesday night through Wednesday
morning for IAZ004>007-015>017-023>028-033>039-044>050.

&&

$$

DISCUSSION...Ansorge
AVIATION...Ansorge