Modesto, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.6 °C (low) to 17.5 °C (high). Annual precipitation averages 1008.4 Millimeters. Modesto is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.7 °C | 2.1 °C | 56.13 mm |
| February | -4.8 °C | 4.9 °C | 51.05 mm |
| March | 0.2 °C | 11.2 °C | 73.15 mm |
| April | 6.1 °C | 18.2 °C | 111 mm |
| May | 12.4 °C | 23.7 °C | 121.92 mm |
| June | 17.5 °C | 28.4 °C | 114.3 mm |
| July | 19.2 °C | 30.1 °C | 93.73 mm |
| August | 18 °C | 29.4 °C | 84.33 mm |
| September | 13.3 °C | 26.5 °C | 83.57 mm |
| October | 7.1 °C | 19.7 °C | 81.28 mm |
| November | 1.2 °C | 11.3 °C | 80.26 mm |
| December | -3.8 °C | 4.8 °C | 57.66 mm |
| Annual | 6.6 °C | 17.5 °C | 1008.38 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |