According to the National Centers for Environmental Information (NCEI), the average April temperature in Illinois has warmed by 2 degrees over the last century. In addition, the most recent decade of 2006-2015 was the warmest set of Aprils on record. Statewide records go back to 1895.
Here are the statewide average temperatures for April in Illinois plotted by year. The purple line and black dots show the year-to-year variability in April temperatures in Illinois. The blue line shows the upward trend. You can find the original data and graph here.
While there were a few cold stretches in April, the statewide average temperature for the month was 54.1 degrees, 1.7 degrees above average.
Precipitation in Illinois for April was more complicated. April precipitation was in the range of two to four inches in northern and central Illinois, and 4 to 7 inches in southern Illinois. As a result, the northern two-thirds of the state was slightly below average while the southern third was up to 2 inches above average. Fort Massac State Park reported the highest monthly precipitation total of 7.80 inches.
April Precipitation. Click to enlarge.
April Precipitation Departure. Click to enlarge.
When I give talks on climate and climate change, I often get questions about volcanoes and their impact on our climate. The Washington Post had a recent article on the subject, mentioning the famous eruption of Tambora in 1815, which in 1816 led to the year without a summer in the eastern US. It probably had impacts on Illinois but we had no widespread observations in place at the time.
The one I remember the best was Mount Pinatubo. The following summer after that eruption was exceptionally cool across the US and around the world.
Summer 1992 temperature departures from average for the lower 48 states. Shades of green indicate level of coolness. Click to enlarge.
Climate.gov just posted an interesting video on Charles David Keeling and his ground-breaking measurements of CO2 levels in the atmosphere. The observatory was located on Mauna Loa, on top of the second highest peak in the Hawaiian Islands.
The idea behind the site was to keep it far removed from any nearby sources of CO2 resulting from human activity. Because of it’s location and longevity, it is our best measurement of the background CO2 levels in the lower atmosphere. Here is the link to the Mauna Loa Observatory records and trends.
Dr. Keeling received his undergraduate degree here at the University of Illinois in 1948 and his Ph.D. in Chemistry at Northwestern in 1954. There is a brief bio here.
Here are maps showing how April so far has been warmer and wetter than average across Illinois and the Midwest.
Temperature Departure from Average
Right now, most of the eastern two-thirds of the United States have experienced above-average temperatures for April (first map). The Midwest has been 1 to 6 degrees above-average, depending on the shade of orange (second map). Click on any map to enlarge.
The NOAA Climate Prediction Center has released their monthly and seasonal outlooks for the growing season.
In the near-future, the 6-10 and 8-14 day forecast indicate that colder-than-average conditions will prevail for the next two weeks. For precipitation, there is an increased chance of drier-than-average conditions in parts of northern Illinois for the next two weeks.
There is not a lot to report for Illinois at the medium range. We are in equal chances (EC) for above-, below-, and near-average temperature and precipitation for both May and the 3-month period of May-July.
According to the National Weather Service report on the April 9, 2015, tornadoes, the tornado that tracked through Fairdale was rated EF-4 on the Enhanced Fujita scale. This would be the first EF-4 tornado in April since 1981 for Illinois and only the 33rd in Illinois history, regardless of month, since reliable records began in 1950.
According to the NWS Storm Prediction Center database, only 33 F/EF-4 tornadoes have struck Illinois since 1950. Even more rare, only 8 have hit Illinois in April. Of those eight in April, six struck in the 1960s, one in 1981, and one in 2015:
Here are all the F/EF-4 tracks for Illinois from 1950-2014, from the MRCC tornado tracker tool. Unfortunately, we cannot screen out just the April events at this time. While this is a screenshot of the tool, the actual tool allows you to zoom in and out. If you point to a track then you get a pop up window with the details of that track. Check out the tornado tracker tool – it’s free.