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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Eighth Coldest January on Record for Illinois

Temperature

Based on preliminary evidence, January 2014 was the eighth coldest January on record for Illinois. The statewide average temperature was 18.2 degrees, 8.1 degrees below the 1981-2010 average of 26.3 degrees. The statewide records go back to 1895.

Coldest January’s on Record

  1. January 1977: 10.3°F
  2. January 1918: 11.6°F
  3. January 1979: 12.9°F
  4. January 1912: 13.9°F
  5. January 1940: 13.9°F
  6. January 1978: 16.0°F
  7. January 1963 and 1982: 16.7°F
  8. January 1970, 1985, and 2014: 18.2°F

After being largely absent for the past two winters, below-zero temperatures were common in January 2014. For example, in Chicago the low temperature was zero or below on 13 days at O’Hare Airport. The low temperature was below freezing (32 degrees) every day of the month at Chicago.

Snowfall and Precipitation

Snowfall for January was above-average for most of the state, except far southern Illinois. Amounts ranged from 1-6 inches in far southern Illinois to 25-30 inches in northeast Illinois (getting a boost from lake-effect snow). The rest of the state saw snowfall totals in the 10-20 inch range. Chicago reported 33.5 inches of snow through Thursday, the third snowiest January on record. And it’s still snowing at the time of this report on Friday morning. The Chicago snowfall records go back to 1888.

The combination of the water content of the snow and a few rain events resulted in a state-wide precipitation total of 1.76 inches, which is just slightly below the long-term average of 2.12 inches. However, some areas of the state were below-average in January, especially south of Interstate 70 where winter-time precipitation is typically heavier than this year.

Snowfall (left) and snowfall departures from average (right). Click to enlarge.

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