Chicago weather by month
Chicago runs from about -4°C in January to 23°C in August, with July the wettest month at 172 mm.
warmest month
August
23°C
coolest month
January
-4°C
wettest month
July
172 mm
worst air month
July
15 µg/m³
The whole year, month by month.
| Month | Avg temp | Rain | Sun | PM2.5 |
|---|---|---|---|---|
| January | -4°C | 109 mm | 147 h | 9 |
| February | 2°C | 17 mm | 265 h | 15 |
| March | 5°C | 119 mm | 274 h | 11 |
| April | 10°C | 110 mm | 267 h | 10 |
| May | 16°C | 98 mm | 368 h | 9 |
| June | 22°C | 73 mm | 352 h | 11 |
| July | 23°C | 172 mm | 359 h | 15 |
| August | 23°C | 70 mm | 370 h | 13 |
| September | 20°C | 67 mm | 306 h | 11 |
| October | 15°C | 54 mm | 304 h | 7 |
| November | 8°C | 95 mm | 148 h | 7 |
| December | 0°C | 49 mm | 135 h | 11 |
About 3,295 hours of sun a year. Roughly 104 rainy days a year.
These are long-run climate normals, not a forecast. A given year can sit well outside them. PM2.5 is a global model: near the coast it counts sea salt as fine particulate and reads high against ground stations, sometimes by a factor of two. Use the shape of the year, not the absolute number.
where these numbers come from
- · Temperature, rainfall and sunshine: ECMWF ERA5 reanalysis climate normals via Open-Meteo (CC BY 4.0), fetched once and stored.
- · PM2.5: Copernicus CAMS reanalysis, monthly means. Modelled, not station readings; near coasts CAMS counts sea salt as PM2.5 and reads high.
Last reviewed 2026-05-23. Full method, licences and the list of sources we rejected are on the methodology page.