textproduct: Des Moines

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.