Hanover, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 3.4 °C (low) to 14.8 °C (high). Annual precipitation averages 968.8 Millimeters. Hanover is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.3 °C | -1.9 °C | 34.8 mm |
| February | -9.4 °C | 0.6 °C | 41.4 mm |
| March | -3.3 °C | 7.7 °C | 55.88 mm |
| April | 2.7 °C | 15.1 °C | 96.27 mm |
| May | 9.2 °C | 21.6 °C | 110.24 mm |
| June | 14.9 °C | 27 °C | 145.29 mm |
| July | 16.9 °C | 28.7 °C | 115.06 mm |
| August | 15.7 °C | 27.7 °C | 98.55 mm |
| September | 10.9 °C | 24.1 °C | 93.73 mm |
| October | 4.6 °C | 16.9 °C | 74.93 mm |
| November | -1.8 °C | 8.3 °C | 57.66 mm |
| December | -7.8 °C | 1.2 °C | 44.96 mm |
| Annual | 3.4 °C | 14.8 °C | 968.77 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |