Annawan, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 40.2 °F (low) to 60 °F (high). Annual precipitation averages 38.6 Inches. Annawan is located in USDA Plant Hardiness Zone 5b. 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 | 14.3 °F | 30.3 °F | 1.77 in. |
| February | 17.7 °F | 34.8 °F | 1.89 in. |
| March | 28.1 °F | 47.6 °F | 2.44 in. |
| April | 38.9 °F | 61.1 °F | 3.79 in. |
| May | 50.7 °F | 72.3 °F | 4.93 in. |
| June | 60.6 °F | 81.3 °F | 4.84 in. |
| July | 64.0 °F | 84.3 °F | 3.99 in. |
| August | 61.8 °F | 82.7 °F | 3.92 in. |
| September | 53.4 °F | 76.8 °F | 3.58 in. |
| October | 41.9 °F | 64.1 °F | 2.94 in. |
| November | 30.4 °F | 48.7 °F | 2.43 in. |
| December | 20.2 °F | 35.8 °F | 2.04 in. |
| Annual | 40.2 °F | 60 °F | 38.56 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |