Illinois in 2012 – Second Warmest and Tenth Driest on Record

2012 Summary

The year 2012 will long be remembered for the drought and the exceptionally warm temperatures. While the data for December is still preliminary, it was the second warmest and tenth driest year on record for Illinois.
The statewide average temperature for 2012 was 55.5 degrees, 3.3 degrees above normal and the second warmest year on record for Illinois. The warmest year was 1921 with 55.6 degrees. Temperatures were much warmer than normal in January-May, July, and December (figure below). For some places in Illinois it was the warmest year on record, including Chicago and Rockford (see story here).
The statewide average precipitation for 2012 was 30.37 inches. That was 9.83 inches below normal and the 10th driest year on record in Illinois. The normal annual precipitation in Illinois is 40.20 inches.  Precipitation was much drier than normal in May-July and November (figure below). Here is how 2012 compared with other dry years:

  1. 1901 – 26.34″
  2. 1930 – 27.88″
  3. 1963 – 28.00″
  4. 1953 – 28.05″
  5. 1914 – 28.58″
  6. 1976 – 28.84
  7. 1940 – 29.33″
  8. 1988 – 29.71″
  9. 1936 – 30.24″
  10. 2012 – 30.37″

The map of the precipitation departures from normal across the state (below), as of December 31, 2012, shows large areas of the state with deficits in the range of 8 to 16 inches below normal (the darker tan and bright red colors) for 2012.
Unfortunately, winter is our driest time of year in Illinois.  The normal precipitation for January and February is 2.11 and 2.12 inches, respectively. Even March is not much wetter at 2.98 inches. That adds up to 7.21 inches for those three months combined. It would take something close to record precipitation in January (6.92 inches), February (4.46 inches), and March (7.53 inches), for a total of 18.91 inches, to erase the deficits accumulated in 2012.

December 2012

The statewide average precipitation for December 2012 was 2.34 inches, just 0.4 inches below normal.
The statewide average temperature for December 2012 was 35.8 degrees, 5.9 degrees above normal and the  13th warmest December on record. The warmest December on record was 1923 with 39.7 degrees.


Click to enlarge.

9 Replies to “Illinois in 2012 – Second Warmest and Tenth Driest on Record”

  1. How do you account for changes in UHI when comparing records today with those in the past?

  2. I think it is important that we not use terms like “normal” when referring to climates. There is no “normal” in climate, only averages over time, and we have only just begun to monitor climates in detail. Anyone who has studied geology can tell you that climates change, and in wild fashion.

  3. That’s a good question, most of the stations in Illinois are in rural locations or small towns. The one area where I do worry about the effect of the urban heat island (UHI as you called it) are in the locations nearest to Chicago. Many areas in the counties bordering Cook have seen considerable growth in recent decades. If I were just looking in the northeast part of the state it would be something to consider more carefully, but less so for the statewide average. Thanks for reminding me of this topic and if I can get away from my drought duties this winter I will devote a post specifically to this important issue.

  4. The convention I’m following here in the blog is to refer specifically to the 30-year average, updated every 10 years (that means 1981-2010) as normal. It was updated every 10 years to capture the more recent changes in climate. We could make averages any length we want. In fact, averages of 10 years updated every year are used in some applications.
    But back to the use of the word normal. If you look at, “normal” as a noun is defined under section 7 as “the average or mean”. That is how we came to use the word “normal” in this context. As an adjective, it can mean “usual … regular … natural”, which I think is where you were heading with your comment.

  5. I forgot to add a final thought … you’re point is well taken and I’ll be more explicit in future blog posts that when the word normal is used it means the 1981-2010 average.

  6. Thanks for the thoughtful reply Jim!
    My concern is that the public does not understand your idea of “normal”, and usage “normal” instead of “average” leads them to believe that anything outside of the observed average is “abnormal”. There is far too much climate hysteria these days, and it is important for us to speak precisely, so as not to mislead the layman. After all, there is nothing unusual or unprecedented about our current climate, or how we got here.
    When I took my first climatology class, I had already been a geology student for many years, and I was immediately struck at how my professor presented our planet’s climates as static. I also worked on a farm while attending college, and knew firsthand that something as simple as land usage can change climates. Ever laid irrigation pipes in a cornfield in late July?
    Weather stations only measure their immediate surroundings, and our attempts to discover an “average” is far from perfect, as you can find many stations whose temperatures have not risen at all in a century. And then there is this…
    “Using data downloaded from NASA GISS and picking rural sites near, but not too near, to urban sites, a comparison has been made of the temperature trend over time of the rural sites compared to those of the urban sites. 28 pairs of sites across the U.S. were compared. The paired rural site is from 31 to 91 km from the urban site in each pair. The result is that urban and rural sites were similar in 1900, with the urban sites slightly higher.”
    So it appears that Sundance’s concern is valid, what we really have here are land use change issues, and there is nothing “abnormal” about our climate. Nothing outside of “normal”, or natural, variability.
    I used to be able to access individual raw weather station data here…
    … and had myself located many stations with zero temperature rise in a century. But GISS is doing their best to conceal and alter the raw data, and mislead Americans about our national climate heritage. Honesty is the best policy, but it is not GISS policy.
    It would be most honest and beneficial to society, for us to use the most precise language available such as “observed average”, and not leave things open to wild interpretation through loose definition.
    Thanks again for your reply.

  7. Weather reports are obsessing about the lack of snowfall in the Chicago area, but I am more interested in total precip at reporting stations as we’ve had several decent rain events since December 1. Why don’t forecasters provide total precip stats, which provides a more complete picture than just snow. For my part, I’d rather have precip in the form of rain instead of snow, particularly when it’s not been cold enough long enough to freeze the ground and have it all runoff.

  8. Good point Chris. The lack of snow this winter has certainly grabbed the attention of the media. As far as addressing drought concerns, getting it as rain rather than snow is ok by me. That’s especially true if the ground has not frozen yet.

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