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.

Snowfall

A few areas in northeast Illinois have received over 5 inches of snow. The largest totals for the month are CocoRaHS stations near Downers Grove (IL-DP-127) and Elgin (IL-KN-95), both with 7.4 inches. Amounts of 3 to 6 inches were common across northern and eastern Illinois. Meanwhile, many parts of western Illinois have received less than 2 inches.

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Looking at the accumulated snowfall as a departure from normal (map below), most areas are near to below normal on snowfall. The only area with unusual amounts of snow for their region is far southern Illinois.

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The actual water content of these snowfall amounts are small. Our station here in Champaign reported 3.3 inches of snow in the last event with a water content of only 0.14 inches. That’s a ratio of 24:1 between snowfall and water, far higher than that 10:1 ratio you always hear about on snowfall (10 inches of snow equals 1 inch of water). You can feel the difference when you shovel it off your driveway.

Seasonal Snowfall

Here are the seasonal snowfall totals for this winter so far. Most of the northern half of the state has between 5 and 10 inches of snow (two lightest shades of green), while the most of the southern half, and especially the southwest, has between 1 and 5 inches. Areas in northern and western Illinois are 2 to 6 inches below normal for the season so far.

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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.

 

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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. 

 

Here are the 5 winters with the highest snowfall totals on record for Illinois:

  1. 1978-79 with 44.5 inches
  2. 1977-78 with 44.4 inches
  3. 1911-12 with 39.5 inches
  4. 2013-14 with 39.4 inches
  5. 1959-60 with 38.6 inches

Here are the 5 winters with the lowest snowfall totals on record for Illinois:

  1. 2011-12 with 9.2 inches
  2. 1920-21 with 9.4 inches
  3. 2016-17 with 9.6 inches
  4. 1994-95 with 9.8 inches
  5. 1965-66 with 9.9 inches

Of these 10 winters, I have been around for eight of them. Hey, I’m not that old (yet).

 

 

 

Warm 2017 Ends with a Cold, Dry December in Illinois

Temperature

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.

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December Temperature

More about December – it’s funny to think that up until Christmas Eve, we were enjoying exceptionally mild December weather. Here are the daily temperature departures from 1981-2010 normals in Champaign-Urbana. The rest of Illinois had similar experiences. The end result is that the cold and warm weather more or less balanced out in December, leaving the statewide average temperature for December at 30.4 degrees, 0.5 degrees above normal. I originally posted the following right at the beginning of January “28.9 degrees, 1 degree below normal”, which was based on very preliminary data.

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Precipitation

Annual Precipitation

The statewide average precipitation for 2017 was 37.65 inches, 2.31 inches below normal. However, that obscured several dramatic precipitation events such as the heavy rains in southern Illinois in spring, and in northern Illinois in July and September. Here are the monthly precipitation departures from normal for Illinois. Illinois received 6.86 inches of rain in April, 3.08 inches above normal and the 5th wettest April on record. On the other hand, Illinois experienced its 5th driest September on record with only 0.82 inches, 2.41 inches below normal.

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The map of precipitation departures at the end of 2017 show the areas of concern for Illinois. Some exceptionally dry areas exist in central Illinois, around St. Louis, and parts of southeastern Illinois. These will be areas to watch in spring for the 2018 growing season.

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December Precipitation

Looking closer at December, the statewide average precipitation total was 0.79 inches, 1.90 inches below normal and the 7th driest December on record. Far southern Illinois received 1 to 3 inches of precipitation, but the rest of the state received less than an inch. The figure below shows total precipitation (left panel) and departures from normal (right panel). Click to enlarge.

Snowfall

2017-18 Snowfall

Snowfall for the 2017-18 season got off to a slow start but we started to see some significant accumulations by the end of December. Snowfall totals ranged from 6 to 15 inches in the northern half of the state and down to almost zero snowfall in far southern Illinois by December 31. Cissna Park (Iroquois County) reported the largest winter snowfall total of 15.5 inches. Mt. Carroll (Carroll County) was in second place with 10.8 inches, and Chatsworth (Livingston County) was in third place with 10.5 inches.

Here are the maps of observed (left panel) and departures from normal (right panel) through December 31. Click to enlarge.

December Snowfall

As you can see, most of the snowfall for the 2017-18 season fell in December. The largest totals stretched from the Quad Cities and passed just south of Chicagoland.  Overall the state remained below normal on December snowfall.