With the streak of warm weather this fall, thoughts of snow are far away – but not for much longer. The first significant winter storm for the Midwest is on the horizon on Thursday and Friday. It will likely hit Nebraska, the Dakotas, and Minnesota, but miss Illinois (blue shading on the map below).
So when can we expect to see that first measurable snowfall (0.1 inches or more) in Illinois?
Here is a map that we constructed a few years ago using data from 1971-2000. No surprise – the earliest dates are in the Chicago area and cluster around November 20. For the rest of the northern half of the state, the average date is towards the end of November. In central Illinois, I have always considered Thanksgiving to be the start of the snowfall season. The average dates get dramatically later as you go southward, getting closer to Christmas by the time you get to Carbondale and southward.
These are average dates but the dates in a particular year can be much earlier or later. For example in Chicago, the date of the first snow ranges from October 12 to December 20 based on data from 1884 to present.
Normal November Snowfall
The early accumulations of snow are usually very modest in Illinois. Here is normal, or average, snowfall in November across Illinois, ranging from 1 to 2 inches in far northern Illinois to less than an inch for the rest of the state. The normal snowfall for November in far southern Illinois is zero. Notice that several of the sites in the southern half of the state have normal snowfall amounts greater than zero even though their average start dates are in December. In those cases, there were enough early snowfalls in November to affect the average snowfall in November.