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.

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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.

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New Outlook for December – Wetter, Colder in Illinois

The NWS released their latest outlook for December. They have Illinois with equal chances (EC) of above, below, and near-normal temperatures for the entire month. However, the day to day forecasts out to 14 days show Illinois having colder than normal temperatures on most of the days. The NWS product for weeks 3 and 4 suggest that warmer-than-normal weather will return in the second half of December. In general, I have higher confidence in the forecasts out to 14 days.

The December outlook also shows Illinois with an increased chance of being wetter than normal. This is true in the shorter range forecasts out to 14 days as well. Considering it’s December, a forecast of colder and wetter than normal conditions sure sounds like a recipe for snow. As you may recall, last December was notable for having almost no snow.

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Will It Ever Snow Again in Illinois?

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).

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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.

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February Snowfall in Illinois

Much of the southern third of Illinois received between 1 and 12 inches in this last winter storm. The highest amount reported was 12.5 inches at Smithland with several other stations reporting in the 7 to 8 inch range, including Jerseyville with 7.8 inches, Newton with 7.8 inches, and Brookport Dam with 8.8 inches.

map1The northern third of Illinois received a considerable amount of snow from the January 31 – February 2, 2015 storm.

As a result, total February snowfall has ranged from 15 to 20 inches in northeast Illinois and widespread amounts of 5 to 15 inches across the state (first map below). As a result for the month to date, most of the state is 1 to 8 inches above average except for the northeast which is 8 to 12 inches above average (second map below).

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First Half of May in Illinois – Warm, Wet, And Then Snow

According to preliminary records, the first half of May was both warmer and wetter than average for many locations in Illinois. The statewide average temperature was 61.2 degrees, about 1.4 degrees above average. Meanwhile, this morning there are reports of snow falling in northern Illinois. Talk about weather extremes. This was after last weekend when we saw widespread reports of highs in the upper 80s and low 90s.

The statewide average precipitation was 2.43 inches, 18 percent above average. Here is a screenshot of the last 14 days showing the widespread and heavy rainfall in much of the northeast, east-central, and southern parts of Illinois with many sites reporting between 3 to 6 inches of rain. Parts of western and central Illinois have not been as wet with amounts in the range of 1 to 3 inches of rain.
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Snow in May? Read more on the Chicago NWS page. It looks like Rockford set a new record for the latest report of snowfall in the season. The Chicago record still stands at June 2, 1910.

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Map courtesy of the Chicago NWS office.

First Half of February – Cold and Snowy

It is Valentine’s Day. It is also halfway through February. The statewide average temperature so far in February is 11.5 degrees, 14 degrees below the long-term average.

The accumulated snowfall for February 1-14, 2014, ranges from 4 to 5 inches in far southern Illinois to and from 5 to 15 inches in the rest of the state. The band of heaviest snow extends from Quincy to Chicago with amounts of 12 to 15 inches.

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The long-term average (1981-2010) February snowfall is presented in this map below. Comparing it with what snow has fallen so far shows that many places have already exceeded their February average by more than double.

Click to enlarge. Illinois State Climatologist Office.  ISWS.
Click to enlarge. Illinois State Climatologist Office. ISWS.

Right now almost all of Illinois is covered in snow, as shown by this image from the National Operational Hydrologic Remote Sensing Center. Southern Illinois is covered by 1 to 4 inches of snow, central Illinois by 4 to 10 inches, and northern Illinois by 10 to 20 inches.

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Click to enlarge. NWS National Operational Hydrologic Remote Sensing Center.

The water content of that snow pack is substantial in the northern half of the state with amounts of 1 to 4 inches (first map below) with higher amounts in states to the north, and upstream, of Illinois (second map). According to the National Weather Service, temperature are expected to be much warmer in the coming week with highs across the state above freezing from Monday through Thursday along with the possibility of rain. It is possible that the snow pack will be greatly reduced by the end of the week and likely gone for many areas in the southern and central Illinois.

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Click to enlarge. NWS National Operational Hydrologic Remote Sensing Center.

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