Simpson, Illinois has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 47 °F (low) to 67.2 °F (high). Annual precipitation averages 50.7 Inches. Simpson is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 25.4 °F | 42.2 °F | 3.85 in. |
| February | 28.3 °F | 46.6 °F | 3.45 in. |
| March | 36.5 °F | 56.4 °F | 4.66 in. |
| April | 46.1 °F | 68.4 °F | 5.43 in. |
| May | 56.4 °F | 76.8 °F | 5.29 in. |
| June | 64.8 °F | 85.1 °F | 4.58 in. |
| July | 68.5 °F | 88.2 °F | 4.24 in. |
| August | 66.3 °F | 87.3 °F | 3.14 in. |
| September | 58.6 °F | 81.8 °F | 3.53 in. |
| October | 47.0 °F | 70.9 °F | 3.75 in. |
| November | 36.5 °F | 56.9 °F | 4.43 in. |
| December | 29.1 °F | 46.0 °F | 4.32 in. |
| Annual | 47 °F | 67.2 °F | 50.67 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |