647
FXUS63 KDMX 062259 AAA
AFDDMX

Area Forecast Discussion...UPDATED
National Weather Service Des Moines IA
459 PM CST Sat Dec 6 2025

.KEY MESSAGES...

- Snow this afternoon and tonight. A band of heavy snowfall is
  expected.

- Colder on Sunday with highs in the single digits north to low
  20s south.

- Above freezing on Tuesday followed by another cold front and
  strong winds Tuesday night. Light snow or snow showers are
  also possible.

&&

.UPDATE...
Issued at 459 PM CST Sat Dec 6 2025

A band of heavy snow with rates of 1 to 1.5 inches per hour has
set up from Storm Lake east southeast to the northern Des
Moines metro area. Visibilities have fallen to less than 1/4
mile in places and this band is expected to remain in place for
the next few hours, leading to heavy accumulations. Expanded the
Winter Storm Warning south to include Boone, Calhoun, Story,
and Marshall counties. 6 to 8 inches are expected in the warned
area.

&&

.DISCUSSION...
Issued at 221 PM CST Sat Dec 6 2025

Narrowing down the area of the heaviest snow band for the rest of
this afternoon and into the evening is the forecast challenge.
Individual deterministic models are varying slightly yet on the area
of max precipitation which will have impacts on further headline
updates.

The incoming system has plenty of kinematic forcing with the mid-
level short wave along with a 35 to 40 kt low level jet pointed
into central Iowa. A ribbon of strong theta-e advection will
setup on the nose of the low level jet (LLJ) and this
intersection with the speed convergence, mid-level ascent and
the thermodynamics will produce an area with impressive vertical
ascent. Snow is moving into northwest and west central Iowa
this afternoon. The max reflectivity on KFSD radar is matching
up well with the dendritic growth layer vertical ascent. This is
also occurring along that LLJ nose. The LLJ will move east and
broaden a bit. This along with the intensification of the
theta-e ribbon should lead to the snow axis to pivot more
easterly. Following the max vertical ascent through the
dendritic layer, assuming saturation, places the heaviest snow
axis rough in the Highway 20 to Highway 30 corridor region with
it angled WNW to ESE. This is roughly from Pocahontas to Fort
Dodge to Eldora and perhaps northern Tama County. Calhoun and
Tama counties are not currently in the warning but the northern
portions of those areas may approach 6 inches so an upgrade may
be required. Snowfall rates of one to one and one half inches
per hour may occur with much of the snow occurring in a 4 to 6
hour time period. Lowered snow amounts a bit over far northern
Iowa where amounts may be closer to 3 to 6 inches. Not planning
any downgrade at this point and the snowfall rates along with
still create hazardous travel conditions. Further south along
the Interstate 80 corridor, there is the potential for a brief
period of freezing drizzle after the snow ends as the mid-
levels drying occurs with the passage of the mid-level short
wave. Far south may have a mix of rain and snow as surface-wet
bulb values approach 34 degrees along with melting layer around
3-4 kft. The far south could have some fog in the null wind axis
before the cold advection arrives. Enough gusty winds are
possible north for some blowing snow but at this time, not
expecting much for visibility reductions.

Sunday will be colder with highs in the single digits north to 20s
south. Early morning wind chills north will be in the teens below
zero. Warm advection will occur Monday and Tuesday. Temperatures
should be above freezing area wide Tuesday ahead of the next clipper
system. That clipper arrives Tuesday night and will drag more cold
air into the state. The precipitation with this system should remain
mostly in the northeast side of the system, which is mostly into
Minnesota and Wisconsin though some light snow is possible into
parts of Iowa. Strong and gusty winds are also possible with this
system. Some deterministic proximity soundings including the
GFS/ECMWF are showing 45+ kts in the mixed layer. In addition, some
low level instability is beginning to show up which is leading to
the snow squall parameter to start pinging some potential for snow
showers/gusty winds. The remainder of the forecast period features
northwest flow and potentially more snow late next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1135 AM CST Sat Dec 6 2025

Conditions will continue to deteriorate through the afternoon
and evening from west to east as lowering cigs and areas of snow
develop. IFR or lower conditions are expected at times for all
locations. KFOD/KALO and possibly KMCW may have periods with
vsby less than one quarter mile at times due to falling snow.
The snow will mostly end by mid to late evening. Will continue
to monitor for the potential for a brief period of freezing
drizzle near KDSM/KOTM around 06z. Cigs will begin to improve
late in the period. The wind may be gusty at times tonight into
Sunday morning which may produce shallow blowing snow.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until midnight CST tonight for IAZ004-005-
015-016-023>025-034>036-047.
Winter Weather Advisory until midnight CST tonight for IAZ006-
033-044>046-057>059-071-072.
Winter Weather Advisory until 6 AM CST Sunday for IAZ007-
060>062-073>075-085-086.
Winter Storm Warning until 6 AM CST Sunday for IAZ017-026>028-
037>039-048>050.

&&

$$

UPDATE...Borghoff
DISCUSSION...Donavon
AVIATION...Donavon