Prophetstown, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 39.8 °F (low) to 59.5 °F (high). Annual precipitation averages 38.9 Inches. Prophetstown is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 13.2 °F | 29.7 °F | 1.68 in. |
| February | 17.1 °F | 34.2 °F | 1.77 in. |
| March | 27.8 °F | 46.9 °F | 2.66 in. |
| April | 38.6 °F | 60.5 °F | 3.76 in. |
| May | 50.5 °F | 71.9 °F | 4.88 in. |
| June | 60.4 °F | 81.1 °F | 5.1 in. |
| July | 63.8 °F | 84.3 °F | 4.08 in. |
| August | 61.6 °F | 82.5 °F | 4.23 in. |
| September | 53.1 °F | 76.3 °F | 3.52 in. |
| October | 41.6 °F | 63.4 °F | 3.05 in. |
| November | 30.0 °F | 48.0 °F | 2.15 in. |
| December | 19.8 °F | 35.2 °F | 2.03 in. |
| Annual | 39.8 °F | 59.5 °F | 38.91 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 |