Cold Start to April in Illinois

The statewide average temperature for Illinois from April 1-11 was 35.6 degrees, 12 degrees below normal. While we are having a few days of warm weather now, we are expected to get right back into colder weather over the weekend. The NWS forecast for the next 14 days shows an overall picture of below-normal temperatures. Even so, I expect the departures from normal won’t be quite as severe as the first 10 days of April.
If you are thinking that you have never seen an April this cold, you are probably right. Here are the top ten coldest Aprils in Illinois. You have to go back to 1983 and 1982 for some really cold Aprils.

Rank Year Average Normal Departure
1 1907 43.1 52.6 -9.5
2 1926 45.2 52.6 -7.4
3 1904 45.6 52.6 -7.0
4 1950 45.8 52.6 -6.8
5 1920 45.9 52.6 -6.7
6 1961 46.6 52.6 -6.0
7 1918 46.7 52.6 -5.9
8 1983 46.8 52.6 -5.8
9 1982 47.0 52.6 -5.6
10 1928 47.4 52.6 -5.2

The past is not always the key to the future. You may have noticed that 1983 (#8) is on the list and was a hot, dry growing season in Illinois. However, 1982 (#9) is on the list as well and was a cool, wet growing season in Illinois. I hesitate to draw any conclusions from the other cases because most of them are from the first half of the 20th century when Illinois was generally cooler and drier, so naturally, those subsequent growing seasons were cooler than normal by today’s standards.
Another thing to consider is that while the central US has been very cold in April, it has not been the case in other parts of the US, especially the Southwest. I suggest we build a twin pipeline to New Mexico and exchange some of our cold air with some of their very warm air.
map-usa
April temperatures over time in Illinois: If you look at April temperatures in Illinois since 1895 (graph below), there has been a warming trend (blue line) of 2.1 degrees per century, which makes this April even more unusual. The gray horizontal line is the 1981-2010 average (aka normal). Remember, one cold April does not make or break a long-term climate trend.
April-trend
 

6 Replies to “Cold Start to April in Illinois”

  1. “The statewide average temperature for Illinois from April 1-11 was 35.6 degrees, 12 degrees below normal.”
    12 degrees below the recorded average would be the correct way to phrase this. There are no “normals” in climate or weather, only averages over time.

  2. I apologize – busy with other projects. The term “normal” is a widely used national and international standard for describing the climate of a region and has been in use for quite some time in those two fields. By using the word “normal” we means something specific – as in “the average based on a 30-year period updated every decade as prescribed by the World Meteorological Society and currently reflects the period of 1981-2010”. In other words, it is shorthand for a specific process and provide more information that saying “an average”.
    If you really want to dig into the history of climate normals, check out https://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/climate-normals/1981-2010-normals-data

  3. Thanks for the reply Jim! Using normal when describing temperatures would suggest that there are “abnormal” temperatures, which of course there are not.
    When I was a climatology student we used “average” to describe temperatures, so as not to confuse the public at large. With all the alarmism out there today, those of us in the know owe it to our fellow citizens to speak as clearly as possible on a subject as loaded as climate change.
    There are many words that are misused today, and that’s a shame as we enjoy likely the most descriptive language on Earth. Some misuse is ignorance, but much of it is intentional.
    All the best!
    He who controls the language controls thought.

  4. I am not misusing the word “normal”. I’m using it as a noun with a specific, clearly defined technical definition that is widely used in the field. Saying we are 2.1 degrees above normal is not the same as saying that it is abnormal. That’s another topic entirely. It’s clear that you have another agenda in mind. I’m not going down that road and will post no more discussion on this subject.

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