Smithboro, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 44.5 °F (low) to 64.7 °F (high). Annual precipitation averages 42.9 Inches. Smithboro 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 | 21.2 °F | 37.5 °F | 2.86 in. |
| February | 24.7 °F | 42.7 °F | 2.41 in. |
| March | 33.5 °F | 53.4 °F | 3.19 in. |
| April | 43.8 °F | 65.6 °F | 4.84 in. |
| May | 54.7 °F | 75.3 °F | 4.95 in. |
| June | 63.5 °F | 84.3 °F | 4.53 in. |
| July | 66.8 °F | 87.4 °F | 4.09 in. |
| August | 64.3 °F | 86.2 °F | 3.37 in. |
| September | 56.0 °F | 80.3 °F | 3.19 in. |
| October | 44.4 °F | 68.3 °F | 3.2 in. |
| November | 34.4 °F | 53.7 °F | 3.56 in. |
| December | 26.1 °F | 42.2 °F | 2.66 in. |
| Annual | 44.5 °F | 64.7 °F | 42.85 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 |