Salem, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 45.1 °F (low) to 65.1 °F (high). Annual precipitation averages 45.3 Inches. Salem 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. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 22.2 °F | 38.5 °F | 3.06 in. |
| February | 25.4 °F | 43.3 °F | 2.55 in. |
| March | 34.2 °F | 53.8 °F | 3.7 in. |
| April | 44.4 °F | 65.9 °F | 4.7 in. |
| May | 55.3 °F | 75.4 °F | 5.02 in. |
| June | 64.1 °F | 84.3 °F | 4.81 in. |
| July | 67.3 °F | 87.3 °F | 4.09 in. |
| August | 64.9 °F | 86.4 °F | 3.57 in. |
| September | 56.6 °F | 80.3 °F | 3.5 in. |
| October | 45.1 °F | 68.8 °F | 3.42 in. |
| November | 35.0 °F | 54.2 °F | 3.9 in. |
| December | 26.9 °F | 42.8 °F | 2.94 in. |
| Annual | 45.1 °F | 65.1 °F | 45.26 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| 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 |