I have noticed that the average date of the first snow is a popular search term on the blog, so here is the reposting of the median dates of the first measurable snowfall of the season in Illinois. This map is based on 1971-2000 data. While it is not based on the current 1981-2010 averages, the map is still relevant for the purpose of getting an idea of the dates. Measurable snowfall means at least a tenth of an inch.
In the northern third of Illinois, the first snowfall occurred around Thanksgiving. The dates switch from November to December once you reach central Illinois (just north of a line between Quincy and Champaign). By the time you reach Carbondale, the date can be as late as December 20. From this you can see that we are by no means behind schedule this year.
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Traces of snow were reported in Chicago and Rockford on October 4. A few years ago I did a post on the earliest and median dates for the first measurable snowfall of the season. Measurable means at least 0.1 inches or more. Snow flurries or traces of snow do not count since they have not been tracked closely in the historical weather records.
No real surprises for anyone who has experienced winter in Illinois. The earliest dates of measurable snow are in the late October, early November time frame. And the median dates range from late November in northern Illinois to the second half of December in southern Illinois. Even so, the dates can vary considerably between nearby sites since many of the early season snows are sporadic and not very widespread.
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