textproduct: Des Moines

KEY MESSAGES

- Widespread dense fog continues tonight into Sunday morning over much of the area. Visibilities of a quarter mile or less are possible.

- Rain and a few rumbles of thunder possible tonight into early Sunday morning, mainly south.

- Falling snow, strong winds and cold temperatures will make travel hazardous on Sunday, especially in northern Iowa. Wind gusts of over 50 mph and blizzard-like conditions are possible near the Iowa/Minnesota border.

DISCUSSION

Issued at 319 PM CST Sat Dec 27 2025

Fog continues to impact much of the forecast area today, with patchy fog in southern and central Iowa, then more widespread dense fog over northern and north central Iowa. These areas of fog will likely persist through the rest of today, with an expansion of the dense fog expected again tonight. The Dense Fog Advisory remains in effect for much of northern and northeastern Iowa and will be in effect again for western, central and southern Iowa again tonight into Sunday morning. Fog will continue into the morning, but will eventually be pushed out by the cold front passing through on mid- day Sunday.

The cold front passage tomorrow will come as a broad 500 mb trough digs in over the central US, pulling cold air down from Canada and generating a deepening surface low across the lower plains region. Ahead of this system will first come a push of warm, moist air, bringing the potential for rain and even a rumble of thunder up into southern Iowa starting early Sunday morning into mid-day. Cold air will also begin to fill in over northwest Iowa on the cold side of the low Sunday morning. This, combined with southwest to northeast oriented bands of strong frontogenetical forcing around 750 to 650 mb will produce bands of snowfall on the cold side of the low. Locally higher snow rates are expected in these bands, but they should be fairly progressive as they move eastward, limiting residence time under the heavier rates. This should help to mitigate significant snow accumulations, although localized amounts around 1 to 2 inches are certainly possible as far south as I-80. The area of greater concern will be farther north, where a broad area of snow will develop in the deformation zone of the deepening low. This will increase the amount of time snow is falling, as well as the eventual amounts. These heavier amounts have been leaking farther and farther south over the last few forecast cycles, increasing confidence in heavier snow amounts in this area. Current forecast has a range of roughly 1 to 4 inches north of highway 20, although recent short range guidance indicates even higher amounts possible along the Iowa/Minnesota border.

Snow accumulations of 1 to 4 inches are enough to cause problems on roadways on their own, but with the strong cold air advection will also come very strong winds behind the cold front tomorrow. Northwesterly winds of 30 to 40 mph are expected, with gusts in excess of 50 mph possible tomorrow afternoon. While the bare ground would theoretically help to negate blowing snow, winds of this strength will still be able to loft freshly fallen snow into the air. This will add an extra layer of impacts to the falling snow, as the gusty winds lead to low visibilities and blizzard like conditions. These impacts will be present both while snow is falling and potentially for a time after, at least until snow is collected into ditches and other storage areas through the evening and overnight. There is also a hint that horizontal convective rolls may develop Sunday evening as low level lapse rates steepen and the entire mixed layer saturates within the dendritic growth zone. These HCRs with the strong winds would produce sudden and drastic changes to visibility for travelers Sunday afternoon and evening. Finally, with the strong winds and colder air mass will come much colder temperatures, especially into Sunday night. Temperatures drop into the single digits and teens, with wind chills in the teens to near twenty below zero overnight, adding yet another layer to the impactful travel conditions, especially for those who become stranded or are working through recovery efforts. Hazardous to potentially dangerous travel is possible in northern Iowa mid-day Sunday through the evening, and actions should be taken to try and avoid travel at these times if at all possible.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1205 PM CST Sat Dec 27 2025

Fog and low stratus continue to produce LIFR or worse conditions at all TAF sites today. These conditions will generally persist into the evening and overnight hours, although brief improvement into MVFR is possible at KDSM and KOTM before fog worsens and ceilings lower again tonight.

A system moving through the area tomorrow will first bring rain chances to the southern half of the state early Sunday morning. A cold front will then pass through the area pushing out the fog and flipping winds from light southeasterly flow to gusty northwesterly flow. The cooler air will also bring a transition from rain to snow. A very brief period of ice pellets and/or freezing rain is possible as this occurs later tomorrow morning, followed by a full changeover to snow. Gusty winds and falling snow may lead to periods of blowing snow, especially near KFOD and KMCW, leading to sharp drops in visibility.

DMX WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until 9 AM CST Sunday for IAZ004>007- 015>017-024>028-036>039-048>050-061-062. Winter Storm Watch from Sunday morning through late Sunday night for IAZ004>007-016-017. Winter Weather Advisory from 9 AM Sunday to 6 AM CST Monday for IAZ015-024>028. Dense Fog Advisory until 6 AM CST Sunday for IAZ023-033>035- 044>047-057>060-070>075-081>086-092>097. Wind Advisory from 9 AM Sunday to 6 AM CST Monday for IAZ023- 033>039-044>050-057>062-070>075-081>086-092>097.