Osco, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 40.3 °F (low) to 59.7 °F (high). Annual precipitation averages 38.4 Inches. Osco 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 | 13.9 °F | 30.0 °F | 1.64 in. |
| February | 17.4 °F | 34.5 °F | 1.85 in. |
| March | 28.0 °F | 47.8 °F | 2.44 in. |
| April | 38.9 °F | 61.1 °F | 3.77 in. |
| May | 50.9 °F | 72.2 °F | 4.92 in. |
| June | 60.9 °F | 81.0 °F | 4.77 in. |
| July | 64.4 °F | 84.0 °F | 4.13 in. |
| August | 62.2 °F | 82.2 °F | 3.9 in. |
| September | 53.9 °F | 76.5 °F | 3.63 in. |
| October | 42.2 °F | 63.6 °F | 2.92 in. |
| November | 30.3 °F | 48.5 °F | 2.39 in. |
| December | 20.0 °F | 35.5 °F | 2.05 in. |
| Annual | 40.3 °F | 59.7 °F | 38.41 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 |