First Half of January – Colder, Snowier than Last Year

Summary: we are halfway through January and so far the statewide average temperature is 16.5 degrees, 7.3 degrees below normal. Last year, by mid-January the average temperatures is 25.2 degrees and 1.4 degrees above normal.

The statewide average precipitation is only 0.6 inches, two-thirds of normal for the first half of January. Last year, by mid-January the average precipitation was 0.82 inches, just 0.07 inches below normal. Note that precipitation is a measure of both the rainfall and the water content of snowfall.

Snowfall has been widespread with 2 to 5 inches common in all but western Illinois. For most areas, that is near to slightly below normal. So far our snow has come from fast-moving low-pressure systems out of Canada (so-called Alberta clippers) that are noted for bringing light, fluffy snow without much water content. Last year, some areas in northern Illinois had received zero snowfall in the first half of January and many areas reported less than an inch. Continue reading


Snowfall Changes Over Time in Illinois

The snowiest winter on record was 1978-79 with a statewide total of 44.5 inches. The winter of 2011-12 had the least amount of snow with a statewide total of 9.2 inches.

While a few stations recorded snowfall in the 1800s, our statewide snowfall records in Illinois began in 1902. There is no long-term trend in the snowfall totals; however, some decades were snowier than others, such as the 1910s, 1960s, and 1970s. In fact, the 1970s were the snowiest decade on record with an average snowfall of 27.2 inches.

Since the 1970s, snowfall amounts dropped steeply with less year to year variability for much of the 1980s and into the early 2000s. However, snowfall amounts in the last six winters have been more variable with the winter of 2013-14 being about as snowy as the late 1970s while the winters of 2011-12 and 2016-17 had the lowest and third lowest snowfall totals, respectively, for the state.


Snowfall is accumulated from July 1 of the first year to June 30 of the second year. The second year is used in the plot and table (for example, 2006 refers to the 2005-2006 season). Illinois State Water Survey, 2018.


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Warm 2017 Ends with a Cold, Dry December in Illinois


Based on preliminary data, 2017 is on track to be the 6th warmest year on record in Illinois with a statewide average temperature of 54.5 degrees, which is 2.2 degrees above normal. This was in spite the very cold ending to December (more on that in a minute). We experienced the warmest February on record with a statewide average of 41 degrees, 10.1 degrees above normal. On the other hand, Illinois experienced its tenth coolest August on record in 2017 with a temperature of 70.5 degrees, 3.1 degrees below normal. Eight out of the 12 months experienced above-normal temperatures.


December Temperature

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Outlook for the Rest of Winter

Summary: So far in December temperatures have been 5.6 degrees above normal, while the statewide average precipitation has been 0.28 inches, a tenth of normal.  The NWS released their outlook for the rest of this winter. Colder than normal conditions are favored in Illinois in January. Colder and wetter conditions favored in January through March. Wetter conditions favored for most of Illinois in April through June.

December (as of 12/21/2017)

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Chances of a White Christmas in Illinois

What are the historical chances of a White Christmas?

We define a “white Christmas” as having at least an inch of snow on the ground on December 25. The map below shows the odds across the state. It should come as no surprise that the highest odds are in northern Illinois.  In general, the odds are about 40-60 percent in the northern third of Illinois, 20-40 percent in central Illinois, and 0-20 percent in southern Illinois.

There can be large differences between nearby sites. Snowfall is notoriously difficult to measure with blowing, drifting, and melting. Two nearby sites may have different results due to exposure to the sun and the wind as well as the dedication of the observer to report on Christmas Day.


What happened last year?

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November in Illinois – Cool and Dry with a Dash of Snow

November Summary

The preliminary numbers are in for Illinois and November was slightly cooler and drier than normal.

The statewide average temperature for November was 41.7 degrees, 0.8 degrees below normal. The warmest reading in the state was 79 degrees at Belleville on November 2. The coldest reading in the state was 11 degrees at Stockton on November 24.

The statewide average precipitation was 2.13 inches, 1.34 inches below normal. The largest precipitation amount was 5.60 inches at Paxton. Some snow was reported in northern and central Illinois. The largest snowfall amount was 1.5 inches at the Chicago Botanic Garden.

Fall (September-November)

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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

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