| Measure | 1961-1990 | 2015-2024 |
|---|---|---|
| Hot days a year, 85.5F or hotter | 10 | 21.7 |
| Days a year at 90F or hotter | 1.9 | 5.9 |
| Average summer high, F | 77.1 | 78.7 |
- Of the 19 cities measured, Chicago added more hot days than 14.
- Its hottest recent summer was 2024.
Questions
What counts as a hot day in Chicago?
85.5F. That was the 90th percentile of a Chicago summer day between 1961 and 1990, so it is a local definition rather than a national one. A fixed national threshold would report almost no change in the coolest cities and almost none in the hottest, which is a property of the threshold and not of the weather.
Is this the temperature record at the airport?
No, and it should not be read as one. These are reanalysis values: a model reconstruction on a grid roughly 31 km across, which is consistent over six decades and between cities in a way station records are not. That consistency is what makes the comparison possible, and it is also why a single day here will not match a thermometer reading.