Osco, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 4.6 °C (low) to 15.4 °C (high). Annual precipitation averages 975.6 Millimeters. 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 | -10.1 °C | -1.1 °C | 41.66 mm |
| February | -8.1 °C | 1.4 °C | 46.99 mm |
| March | -2.2 °C | 8.8 °C | 61.98 mm |
| April | 3.8 °C | 16.2 °C | 95.76 mm |
| May | 10.5 °C | 22.3 °C | 124.97 mm |
| June | 16.1 °C | 27.2 °C | 121.16 mm |
| July | 18 °C | 28.9 °C | 104.9 mm |
| August | 16.8 °C | 27.9 °C | 99.06 mm |
| September | 12.2 °C | 24.7 °C | 92.2 mm |
| October | 5.7 °C | 17.6 °C | 74.17 mm |
| November | -0.9 °C | 9.2 °C | 60.71 mm |
| December | -6.7 °C | 1.9 °C | 52.07 mm |
| Annual | 4.6 °C | 15.4 °C | 975.63 mm |
| 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 : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |