Snow – Date of First Snowfall and Normals for Illinois

Date of First Snowfall

Here are 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 usually occurs around Thanksgiving. The dates move 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.

date of first snow

In about 10 percent of the cases, the first measurable snow occurred as early as November 5 in northern Illinois to November 20 in far southern Illinois.

In about 10 percent of the cases, the first measurable snow occurred as late as December 20 in northern Illinois. South of a line from Quincy to Champaign (Interstate 72), it can occur after the New Year. From Carbondale southward, Illinois, it can be January 20th before the first snow arrives.

How are we doing so far?

Here are the snowfall accumulations so far in the 2017-18 season as of November 27, 2017. I would say that we are not too far off the schedule for snowfall in Illinois.

map

Normal Annual Snowfall Totals (1981-2010)

Here are the normal annual snowfall totals for sites across Illinois. You can find many more maps on normal snowfall by month here and tables of normal snowfall by site here. To give you a rough idea of how the normal snowfall changes across Illinois, it’s close to 3 feet in northern Illinois, 2 feet in central Illinois, and 1 foot in southern Illinois.

Illinois-snow-00ANN-normals

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La Nina and New Winter/Spring Outlooks

Summary: According to NOAA, La Niña has arrived and there is a 65-75 percent chance that it will persist through this winter before fading sometime in the spring. We talked about La Niña in an earlier post here. Illinois has an increased chance of being wetter than normal for this winter and spring with an increased chance of being warmer than normal in spring in central and southern Illinois.

November So Far

November this year is starting out much colder than last year. The statewide average temperature for November 1-16 of this year was 41.7 degrees, 1.4 degrees below normal. Most stations have reported lows below freezing at some point in November and many sites in northern Illinois reached down into the low teens. By contrast, the statewide average temperature for November 1-16 of last year,  was 52.3 degrees, 8.1 degrees above normal. And stations in northern Illinois had only reached down into the mid-20s by this point.

December

The outlook for December is not very interesting for Illinois. We have equal chances (EC) of above-, below-, and near-normal temperatures and precipitation. In other words, there are no clear climate signals to indicate any unusual conditions during December. Wetter than normal conditions are favored in states to the north of us and drier than normal conditions are favored in states to the south of us.  Click on the maps to enlarge.

Winter

For the winter months of December, January, and February, wetter than normal conditions are favored for Illinois, as well as the northern and Great Lakes states. Neither warmer nor colder than normal conditions are favored in Illinois. However, many states to the south of Illinois are favored to be warmer than normal. Northern tier states from Washington to Minnesota are favored to be colder than normal. Hmm, colder and wetter than normal conditions expected in the Dakotas and MN this winter – sure sounds like a recipe for more snow to me.

Spring

For the spring months of March, April, and May, wetter than normal conditions are favored for all of Illinois. Warmer than normal conditions are favored in central and southern Illinois. Meanwhile, neither warmer nor colder than normal conditions are favored in northern Illinois (labeled EC on the map).

 

October in Illinois was 10th Wettest

Based on preliminary data, the statewide average precipitation in Illinois for October was 4.94 inches, 1.70 inches above normal and the 10th wettest October since 1895. The largest monthly total was 15.90 inches of precipitation in Glen Ellyn. Seven other sites in that area reported over a foot of precipitation.

The other noteworthy precipitation event of October was that several sites in northern and central Illinois reported seeing snow on October 28. In most areas, it was nothing measurable, just flurries. However, one station, New Lenox (Will County), did report 0.1 inches. Continue reading