Nelson, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 39.1 °F (low) to 58.9 °F (high). Annual precipitation averages 39.5 Inches. Nelson 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 | 12.9 °F | 29.3 °F | 1.74 in. |
| February | 16.7 °F | 33.9 °F | 1.77 in. |
| March | 27.2 °F | 46.4 °F | 2.41 in. |
| April | 37.8 °F | 59.9 °F | 3.73 in. |
| May | 49.7 °F | 71.3 °F | 4.96 in. |
| June | 59.6 °F | 80.3 °F | 5.39 in. |
| July | 62.8 °F | 83.2 °F | 4.31 in. |
| August | 60.7 °F | 81.6 °F | 4.23 in. |
| September | 52.4 °F | 75.9 °F | 3.78 in. |
| October | 40.7 °F | 62.9 °F | 2.83 in. |
| November | 29.5 °F | 47.6 °F | 2.33 in. |
| December | 19.5 °F | 35.0 °F | 1.98 in. |
| Annual | 39.1 °F | 58.9 °F | 39.46 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 5a : -20°F to -15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |