Today's featured map presents IEM computed and unofficial October 2025 average temperature ranks by climate district for the contiguous US. The pattern shown is rather interesting with below average temperatures confined to each coast and warm values found throughout the middle of the country. Persistent upper troposphere flow patterns lead to persistent areas of warmer or cooler than average air masses, which then nicely appear in monthly aggregate stats like today's feature. The start of November looks to be on the warm side of average for Iowa and surrounding states, much like the start of October was.
As we creep closer to winter and with some hints of snow in the forecast, it is a good time to check in on a simple analysis of daily high and low temperature monthly distributions for Ames partitioned by the presence of snow cover. There are a few caveats including that while the presence of snow cover and the temperatures are reported on the same date, they are not necessarily sequential. For example, a light morning snow cover could melt and the afternoon high temperature be quite mild. Those issues aside, the partitioned distributions are presented as half-violin plots, which attempt to show the most frequent observations by the width of the curve. A simple mean value is plotted as well. There are certainly some strong signals to be found within the plotted analyses and of course, for high temperature some of the difference is a self-fulfilling prophesy requiring cold temperatures to support snow in the first place. The shape of the low temperature distributions is very interesting as you can see snow supporting much colder low temperatures.
For early November, the weather on Monday and especially Tuesday was quite pleasant with highs in the 60s and even a few 70s yesterday. We will have a couple more pleasant days this week before a rude reminder of the upcoming winter season arrives for the weekend. The featured chart is courtesy of the venerable Bufkit Warehouse and shows a time-series of forecast temperatures from various model sources for Des Moines. The times on the x-axis use the meteorological standard of UTC, which is currently six hours ahead of our local central standard time. The slide down in temperatures on Saturday is rather pronounced with forecast highs, at least from the GFS model, on Sunday only in the 30s! There are also chances of snow and the Weather Prediction Center has very small probabilities of four plus inches of snow clipping far northern Iowa on Sunday!
For the Des Moines Airport weather station, the coldest temperature so far this fall season is just 32°F. The featured chart looks into the climatology of season to date coldest low temperature for the site. The blue line represents the 2025 observations. The shaded regions show the distribution of the season to date values over the period of record. The black line represents a simple average. The latest into the season to have a minimum accumulated low temperature of just 32°F is shown to be about two weeks from now. Even with the strong urban heat island effect for the airport sensor, the present weekend forecast shows sub-freezing temperatures to be easily obtained. The chart nicely illustrates how the late August and early September chilly temperatures were below the 25th percentile and much different than has been experienced for the rest of the fall season.
The weather forecast for this weekend brings the coldest temperatures of the season to date along with a decent chance of measurable snowfall on Saturday. The calendar says November and such an event is certainly not out of the ordinary. The featured map plots the percentage of years over each long term climate station's period of record that at least one measurable snowfall event during the month of November. This type of map tends to be a bit noisy due to varying periods of record, difficulties with snowfall measurements, and snow data quality issues. The general north to south pattern is informative with about a 50% chance over southern Iowa and increasing to near 90% over far northern Iowa. The difficulty getting measurable snow tends to be soil temperatures that are still relatively warm and will melt the snow before it can accumulate. For Saturday's event, air temperatures will be hovering near freezing as well, so some parts of the state may only see a chilly rain and no snow.
The first snowfall of the season for Iowa brought a number of inches of snowfall over northwestern Iowa on Saturday. These early season snowfalls tend to be difficult to measure and report as soil temperatures are well above freezing yet. This event also mostly fell during the daytime hours, so pavement temperatures where plenty warm to melt much of the falling snow as well. So the featured map is a bit rough, but the general pattern shown fits available reports over the past 24 hours. The largest total reported was around five inches near Spencer. The first significant cold air of the season also arrived for the weekend with air temperatures and wind chill values both well below freezing. And finally for accounting, the IEM produces these snowfall maps derived from available NWS COOP, Local Storm Reports, and CoCoRaHS observations when snowfall totals of at least two inches are reported and/or significant winter weather impacts are observed. The IEM has been generating these maps for 16 winter seasons now! These maps are generated from Autoplot 207, but get some manual quality control to help produce a refined analysis.
