Thomson, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 39.3 °F (low) to 59.1 °F (high). Annual precipitation averages 37.6 Inches. Thomson 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 | 12.7 °F | 29.3 °F | 1.55 in. |
| February | 16.4 °F | 33.9 °F | 1.72 in. |
| March | 27.4 °F | 46.4 °F | 2.43 in. |
| April | 38.1 °F | 59.8 °F | 3.62 in. |
| May | 49.9 °F | 71.4 °F | 4.48 in. |
| June | 59.9 °F | 80.8 °F | 5.13 in. |
| July | 63.3 °F | 84.0 °F | 4.19 in. |
| August | 61.1 °F | 82.1 °F | 3.87 in. |
| September | 52.6 °F | 75.9 °F | 3.65 in. |
| October | 41.1 °F | 62.8 °F | 2.75 in. |
| November | 29.7 °F | 47.6 °F | 2.27 in. |
| December | 19.4 °F | 34.8 °F | 1.9 in. |
| Annual | 39.3 °F | 59.1 °F | 37.56 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 |