The National Weather Service's Meteorological Summer Summary reports that 2020 was the warmest summer on record in Chicago. When I first read this, I was a little surprised. While I remember two periods of extended high heat, one in July and one in August, 2020 did not feel like a record warm summer. Maybe that is because there were no 100 degree days, or maybe it is because we tend to remember the very hot unpleasant days in a summer and forget about the weeks of below average temperatures. One thing I do know is that I was measuring soil temperatures in the 90's this year for the first time since 2013, so it was definitely warm.
Once I looked at the statistics in detail, it made sense. June, July, and August were all well above average in temperature by 5.0, 5.2, and 4.4 degrees respectively. Other summers with memorable heat waves (like 2012 or 1995) had a few more periods of below average temps to balance out their seasonal averages. When all three summer months are above average by that many degrees, it adds up to a record warm season. We also don't tend to notice nighttime lows as much as daytime highs and 2020 had the 3rd warmest low temperature average on record and the 5th highest high temperature average. Warm nights pump up the average temperature, as well as the soil temperature, without any fanfare but turf managers certainly notice in terms of struggling plants and increased disease and insect pressure.
Even though a lack of rain was occasionally difficult, we were very fortunate that July and August were below average in rainfall and we could keep soil from becoming saturated. Wet soil, flooding, and high heat are a deadly combination for turfgrass, especially in the lower parts of fairways or other areas with less than adequate drainage. Luckily, the heavy rains of May did not continue into the summer months.
The ranking chart below from the NWS report also shows 2010, 2012, and 2020 all in the top 10 of warm summers in Chicago. 2010 and 2012 were much more difficult for turf, at least at Sugar Creek, so I remember them as "hotter," but they were not as far as averages. 2020 was more of an even warmth while 2010 and 2012 contained more extremes in temperature and precipitation.
Below is from the National Weather Service:
| Rank | Year | Mean Average Temperature (°F) |
|---|---|---|
| 1 | 2020 | 76.7 |
| 2 | 1955 | 76.4 |
| 3 | 1995 | 76.3 |
| 4 | 2012 | 76.1 |
| 5 | 1921 | 75.9 |
| 6 | 1949 | 75.5 |
| 7 | 1959 | 75.4 |
| T8 | 2010 | 75.2 |
| T8 | 1973 | 75.2 |
| T8 | 1953 | 75.2 |
- The average high temperature for Summer 2020 in Chicago was 86.2°F, which was the 5th warmest average high temperature for the summer season on record behind 1988 (87.2°F), 2012 (87.0°F), 1995 (86.5°F), and 1955 (86.3°F)
- The average low temperature for Summer 2020 in Chicago was 67.1°F, which was the 3rd warmest average low temperature for the summer season on record behind 1921 (69.7°F) and 1919 (67.8°F)
- There were 30 days this summer in Chicago that had a high temperature of 90°F or higher, which is the 10th most such days in Chicago's history dating back to 1872
- There were 63 days this summer in Chicago that had a high temperature of 85°F or higher, which is the most ever in Chicago's history, besting the previous top number of 61 days that occurred during the summer of 1995
- There were 27 days this summer in Chicago that had a low temperature of 65°F or lower, which ranks as the third fewest in Chicago's history behind 1921 (20 days) and 1919 (24 days)
