First Snow in Illinois

The other night we had a brief period of snow with no accumulation on the ground here in Champaign. However I did see some on my car for a few minutes (see right) before it melted. That reminded me that Zoe and I had worked on some “first snowfall” maps. These maps are based on sites that reported snowfall regularly since 1981. The dates are the earliest and medianĀ dates of the first measurable snow (0.1 inches or more) for the standard averaging period of 1981 to 2010 (also known as “normal”).

No real surprises for anyone who has experienced winter in Illinois. The earliest dates 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.

The median is also known as the 50th percentile and represents in the “middle” of the distribution of dates. In many cases it is a better measure than the average, which can be thrown off by some date that is extraordinarily early or late.

Earliest measurable snow in Illinois for the period from 1981 to 2010. Click to enlarge.

Median date of the first measurable snowfall in Illinois for the period from 1981 to 2010. Click to enlarge.

About Jim Angel

I have been the State Climatologist for Illinois since 1997. I have worked at the Illinois State Water Survey since 1984. The Water Survey is part of the Prairie Research Institute at the University of Illinois.
This entry was posted in Snow and tagged , . Bookmark the permalink.

One Response to First Snow in Illinois

  1. Jim Angel says:

    Reblogged this on Illinois State Climatologist and commented:

    Here is a blog post that I did two years ago about the earliest and median dates of the first measurable snowfall. It is relevant since we just saw traces of snow in Chicago and Rockford on October 4.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s