Olney, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 44.9 °F (low) to 65.3 °F (high). Annual precipitation averages 46.9 Inches. Olney is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 22.4 °F | 38.4 °F | 3.42 in. |
| February | 25.3 °F | 43.4 °F | 2.54 in. |
| March | 33.9 °F | 53.9 °F | 3.98 in. |
| April | 44.2 °F | 66.0 °F | 4.95 in. |
| May | 55.1 °F | 75.7 °F | 5.28 in. |
| June | 63.9 °F | 84.4 °F | 4.9 in. |
| July | 66.7 °F | 87.3 °F | 4.6 in. |
| August | 64.3 °F | 86.4 °F | 2.81 in. |
| September | 56.6 °F | 81.2 °F | 3.32 in. |
| October | 45.1 °F | 69.1 °F | 3.66 in. |
| November | 34.8 °F | 54.5 °F | 4.04 in. |
| December | 26.9 °F | 42.9 °F | 3.4 in. |
| Annual | 44.9 °F | 65.3 °F | 46.9 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -5°F to 0°F |
| Plant Hardiness Zone - 2012 | Zone 6a : -10°F to -5°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |