textproduct: Des Moines

KEY MESSAGES

- Areas of fog over northwest Iowa this morning. A foggy Christmas Eve as widespread fog, possibly dense, develops this evening and lasts into Christmas Day morning.

- Cloudy and mild with drizzle possible at times today through Christmas Day night.

- Cold front moves through Saturday afternoon with conditions turning much colder as it becomes windy into Sunday. The cold will persist into Monday.

UPDATE

Issued at 539 AM CST Wed Dec 24 2025

Visibilities have remained improved over Kossuth, Emmet, and Palo Alto Counties and webcams in the area confirm this as well. So, have cancelled the dense fog advisory. Fog may still redevelop or move over northern Iowa later today, but the more widespread and possibly dense fog looks to develop shortly after sunset making for a foggy Christmas Eve. Latest trends would suggest quarter mile visibility as early as 9pm over portions of northwest and north central Iowa, which expands to much of our forecast area west of I-35 by midnight. Fog forecasting is often not simple and with the stratus lingering around, that could be a potential failure mode for the dense fog to form.

DISCUSSION

Issued at 326 AM CST Wed Dec 24 2025

GOES-East Nighttime Microphysics RGB shows lots of high clouds over the state streaming in from the west as the mid-level ridge becomes centered over the central CONUS. There are a few breaks that allow us to see the low stratus over northern Missouri lifting into far southwest Iowa. There is also an area of fog with visibilities under a mile from around Estherville up to Windom, MN, which is where a Dense Fog Advisory is in effect until early this morning. Surface observations also show lighter fog a bit farther south towards Highway 20. Overall, the dense fog is limited in area with guidance pointing to visibility increasing after sunrise.

Low level theta-e advection is also ongoing and will aid in the stratus lifting into southwest and south central Iowa by around sunrise and will then move northeastward across the state today. Guidance points to visibilities staying up over southern Iowa as the stratus moves in, but will monitor trends as dense fog is present to the south and west of Iowa. As the stratus moves in, there will be a period of at least a few hours where the depth of moisture reaches to around 1km. This depth is on the lower end of favorable drizzle production, but nudgers towards drizzle are the weak omega in the saturated layer and the directional shear for collision coalescence. This looks most likely to occur from southern Iowa this morning moving into eastern Iowa this afternoon, which is where patchy drizzle has been included. Temperatures will be rising, but in a few places over central Iowa later this morning they could be near freezing and will have to monitor temperatures for freezing drizzle potential. Overall, temperatures should be rising so any freezing drizzle window would be short-lived. While temperatures will be above normal and mild, the clouds and drizzle will limit temperatures to the upper 30s over northeast Iowa to the low 50s in far southern Iowa, though depending on the duration of drizzle this may need to be lowered into the 40s. While forecast soundings show the moisture depth becoming shallower by this evening as the wave of theta-e advection pushes east, the near surface moisture remains. Thus, tonight is looking primed for a foggy Christmas Eve as winds become light. Areas of fog may be dense with HREF probability of a quarter mile or less over 60% in portions of north central and western Iowa, which may necessitate a dense fog advisory later today for traveling Iowans and reindeer.

The fog will likely linger into Christmas Day with visibilities improving by mid to late morning, but the cloud cover will remain stout. Temperatures will be similar to today. There will be another chance of drizzle or perhaps light rain as moisture depths increase to around 1km later in in the day into the night with theta-e advection occurring in advance of a weak surface low pressure. This will aid with lift and there is once again weak omega within the saturated layer, but the directional shear does not look as ideal. The clouds will finally begin to decrease through the day Friday over much of southern and western Iowa allowing for some sunshine. Both Friday and Saturday will offer what will likely be the last mild days of 2025 as a more amplified trough moves along the US Canadian border approaching our region. This trough will send a cold front through the state Saturday afternoon into the night. While initial National Blend of Models arrived dry, there are deterministic models and the ensemble means that point to at least some light QPF, which would likely be light snow looking at max low level wet bulb and surface temperatures. In addition, winds from the northwest will quicken as the front passes with gusts over at least 35 mph possible. These winds will deliver much colder air, especially after this mild week, for Sunday into early next week. Highs on Sunday will be anywhere from 15 to 30 degrees lower than Saturday's highs with Monday morning lows in the single digit above zero. Conditions will moderate back closer to normal to end the year.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 539 AM CST Wed Dec 24 2025

Those with flight plans this Christmas Eve, including those from the polar region, will have to contend with ceiling and visibility restrictions over Iowa due to incoming stratus and fog, respectively. VFR conditions are mostly present at the start of this period, but ceilings will lower into MVFR and later IFR from southwest to northeast this morning into this afternoon as stratus and low level moisture spread over the state. Patchy drizzle may occur for a several hour period and looks most likely at DSM, ALO, and OTM later this morning and afternoon. Visibility restrictions due to drizzle or fog are not expected during the daylight hours, but widespread fog will develop tonight with restrictions as low as LIFR and possibly VLIFR. Ceiling restrictions will also slip into LIFR late today into tonight.

DMX WATCHES/WARNINGS/ADVISORIES

None.