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.

 

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)

So far things have been quiet for December in Illinois. The statewide average temperature is 35.5 degrees and 5.6 degrees above normal. Based on the forecasts, we can expect much colder conditions for the rest of December and we will be much closer to the statewide 1981-2010 normal of 29.9 degrees by the end of the month.

The statewide average precipitation is only 0.28 inches (left panel below). That is only about one-tenth of the normal 2.74 inches we receive in December. The driest December on record for Illinois was in 1976 with only 0.44 inches. We could come close to beating that record at the rate we are going.

Snowfall has been light in northern Illinois and mostly a no-show in central and southern Illinois (right panel).  By the way, precipitation is a measure of both the rainfall and the water content in the snow.

OUTLOOKS

January through March

Below are the NWS outlooks for January and January – March. As discussed in previous posts, La Niña conditions prevail in the Pacific and heavily influence the winter forecast.

For January (top row), climate conditions are favorable for colder than normal temperatures across Illinois and the Great Lakes. Meanwhile, there are no indications that January will be either wetter or drier than normal in Illinois. The Ohio River Valley is favored to have wetter than normal conditions in January that includes the far southeastern portion of Illinois.

For January through March, colder than normal conditions are favored in the northern two-thirds of Illinois. The odds are strongest in northeast Illinois (sorry Chicagoland). There are no indications that the southern third of Illinois will be either warmer or colder than normal. Wetter than normal conditions are favored across Illinois as well as the Great Lakes and Ohio River Valley.

The NWS doesn’t do seasonal snowfall forecasts. However, colder and wetter conditions in winter are highly correlated with more snowfall – just saying. My fearless forecast is that we will see more snow than last winter when the state-wide average was only 9.6 inches and the second lowest on record.

 

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April through June

The outlook for April through June (below) shows that warmer than normal conditions are favored in the southern half of Illinois as well as much of the southern two-thirds of the US. Climate conditions do not favor warmer or colder than normal temperatures in northern Illinois.

Most of Illinois is favored to have wetter than normal conditions and is part of the wetter pattern across the Great Lakes region.

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.

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What happened last year?

Areas north of Interstate 80 had snow on the ground Christmas morning, December 25, 2016. Chicago O’Hare reported 2 inches of snow on the ground, while Rockford reported 6 inches. The snow disappeared quickly with the mild weather in late December.

 

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Map courtesy of NOAA at https://www.ncdc.noaa.gov/snow-and-ice/snow-cover/

 

What is the most snow on Christmas Day?

Here are the largest snow depths on Christmas Day (12/25) for selected locations around the state:

  • Chicago, 17 inches in 1951
  • Rockford, 14 inches in 1951 and 2000
  • Quad Cities, 12 inches in 1909
  • Peoria, 10 inches in 1909
  • Springfield, 10 inches in 1915
  • Champaign-Urbana, 9 inches in 1983
  • Carbondale, 9 inches in 2004

What are the odds this year?

Christmas is still 14 days away when this is being written. Single day forecasts that far out, especially for snow are too difficult to make. However, we can get a glimpse of how the models are trending for the week up to Christmas. Temperatures are expected to be near-normal; however, precipitation is expected to be below normal. Therefore, I think the odds of a white Christmas this year look very slim.

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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)

For the traditional fall months of September through November, the statewide average temperature was 56.2 degrees, 1.8 degrees above normal and the 15th warmest fall on record.

The statewide average precipitation for fall was 7.72 inches, which is 2.22 inches below normal. Dry conditions near St. Louis have resulted in the US Drought Monitor calling for moderate drought (D1) to severe drought (D2) from Randolph to Calhoun Counties (see map at end of post).

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Precipitation for November

Here are the precipitation maps for November, accumulated amounts on the first map, departures from normal on the second map. In general, more precipitation fell in eastern and southern Illinois (2 to 4-inch totals were common), than in western and northern (totals less than 2 inches were common).  By the way, precipitation represents both the rainfall and the water content of any snowfall.

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Snowfall for November

Parts of northern and central Illinois received snow in November; however, the amounts were generally less than an inch. As mentioned earlier, the Chicago Botanic Garden near the shores of Lake Michigan received 1.5 inches for the month.

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Temperature Departures for November

Illinois experienced wide swings in temperature in November. In the end, the colder-than-normal and warmer-than-normal days nearly canceled each other out, leaving us just 0.8 degrees below normal for the month. Northern Illinois ended up 1 to 2 degrees below normal (shades of green) while the area around St. Louis was 1 to 2 degrees above normal. These warmer-than-normal temperatures coincided with the area with little precipitation in November.

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US Drought Monitor

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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

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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