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.
