textproduct: Des Moines

KEY MESSAGES

- Light snow will move quickly across Iowa today, with around in inch of accumulation roughly along the Interstate 80 corridor, ranging up to near 3 inches in southeastern Iowa. Winter Weather Advisories are in affect in that area.

- Some flurries or a dusting of snow may occur on Wednesday, followed by much colder temperatures from Wednesday night through Thursday. Low temperatures around sunrise Thursday will range from 10 to 15 below zero across much of the area.

DISCUSSION

Issued at 256 AM CST Mon Dec 1 2025

A surface high pressure area is draped across Iowa and neighboring states early this morning, resulting in very light winds and cool temperatures. Meanwhile, a broad 500 MB trough is approaching from the High Plains, and the broad lift along and ahead of this trough is generating layered clouds that are mitigating overnight cooling and keeping temperatures from falling too far. As gradual saturating of the column continues today light snow will eventually be generated, however it will need to overcome a stout low-level dry layer to reach the surface. Forecast soundings indicate this dry layer is most substantial in our northern counties and less so in the far south, which is also where frontogenetical forcing is more robust. As a result, accumulating snow is more likely in the south/southeast, and have maintained high (70-100%) POPs in that area while trending down and including more flurries in the north/northwest. With the forcing being modest and moving through quite quickly today QPF is low, only around 0.1-0.2" in near the Missouri border. However, forecast soundings indicate several hours with a deep dendritic growth layer below the frontogenetical forcing (which is more toward 600-700 MB), so snow-to-liquid ratios should be fairly high. In other words, while the liquid equivalent precipitation is unimpressive, the snow will be dry and fluffy and accumulate to a bit greater depth than normally anticipated for the QPF. Have maintained SLRs around 18:1 or so and still expect snowfall amounts from around an inch in central Iowa to 2-3 inches in the far south/southeast. Given these relatively low amounts and the expected character of the snow impacts should not be great, however, they may be enhanced by the snow coming on top of remaining snow from the bigger system a couple days ago, and with this being the first work/school day for many after the holiday, the ongoing Advisory is prudent and has been maintained without adjustment. We will be monitoring radar and observational trends today in case forecast snowfall amounts or the Advisory area/timing need to be updated.

Today's shot of light snow will move quickly out around this evening as the 500 MB trough axis moves overhead, yielding to a quieter pattern from tonight through Tuesday. On Tuesday night another broad 500 MB trough will approach from the northwest, while at the surface a large Arctic high pressure area surges southeastward from southern Canada into the Dakotas. The leading push of this high pressure area will form an effective low- level cool front over South Dakota/Minnesota early Tuesday night, which will subsequently push through Iowa around Wednesday morning. The low-level convergence in this effective frontal zone, beneath broad but modest forcing for ascent associated with the approaching 500 MB trough, will generate clouds and light snow late Tuesday night and Wednesday as the system moves through our forecast area. However, moisture will be very limited and forecast soundings do not give much indication beyond flurries or perhaps a light dusting of snow. Some solutions, such as the NAM, do increase frontogenetical forcing along the boundary as it reaches southeastern Iowa Wednesday afternoon, which could result in a quick shot of lightly accumulating snowfall. However, with most models indicating little to no accumulation have maintained lower POPs (20-30%) with no amounts advertised. POPs may need to be raised in subsequent updates, even if amounts do not increase, as it does appear somewhat more likely that flakes will fly even if they do not accumulate.

On Wednesday night and Thursday the large high pressure area will settle right over Iowa, bringing very cold temperatures. The current forecast calls for low temperatures Thursday morning around 10 to 15 below zero across much of our area, with apparent (or "feels like") temperatures approaching 15 below in the south to 20 or 25 below in the north around sunrise. However, winds will be light during this time which will mitigate impacts somewhat. Still, it will be quite a slap in the face this early in the season, and even during the day it will not be much better as forecast highs Thursday afternoon are only in the single digits to lower teens above zero. Bundle up folks.

After the cold high pressure area moves quickly away Thursday night we will see some moderation of temperatures, however, the 500 MB pattern becomes more active with multiple shortwave troughs moving over the region at the end of the week and next weekend. Resolving the details of these systems is ambiguous at this time, but some additional chances for snowfall may ensue. Something to keep an eye on as this week progresses.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 1045 PM CST Sun Nov 30 2025

MVFR to IFR stratus covers much of Iowa, including all TAF sites, however a couple pockets of clear skies remains in place in northwest Iowa and eastern Iowa. While stratus should largely remain in place and begin to expand overnight, some bouncing between flight categories is possible. This is especially true for KALO which is currently on the very edge of an IFR stratus deck and clear skies. Light snow will spread across the southern half of Iowa on Monday, impacting KDSM/KOTM with additional visibility restrictions. Snow tapers off Monday evening but stratus will linger.

DMX WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 9 AM this morning to 9 PM CST this evening for IAZ074-075-084>086-095>097.

Winter Weather Advisory until 6 PM CST this evening for IAZ083- 092>094.