Annapolis, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.7 °C (low) to 18.3 °C (high). Annual precipitation averages 1148.1 Millimeters. Annapolis 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 | -5.9 °C | 3.1 °C | 78.99 mm |
| February | -4.3 °C | 5.9 °C | 62.23 mm |
| March | 0.7 °C | 11.9 °C | 88.14 mm |
| April | 6.4 °C | 18.8 °C | 129.79 mm |
| May | 12.3 °C | 24.3 °C | 122.43 mm |
| June | 17.2 °C | 29.1 °C | 124.21 mm |
| July | 18.7 °C | 30.8 °C | 111 mm |
| August | 17.4 °C | 30.3 °C | 76.96 mm |
| September | 13.2 °C | 27.2 °C | 86.36 mm |
| October | 6.8 °C | 20.3 °C | 93.98 mm |
| November | 1.2 °C | 12.2 °C | 96.01 mm |
| December | -3.3 °C | 5.6 °C | 77.98 mm |
| Annual | 6.7 °C | 18.3 °C | 1148.08 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 |