Salem, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.3 °C (low) to 18.4 °C (high). Annual precipitation averages 1149.6 Millimeters. 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 | -5.4 °C | 3.6 °C | 77.72 mm |
| February | -3.7 °C | 6.3 °C | 64.77 mm |
| March | 1.2 °C | 12.1 °C | 93.98 mm |
| April | 6.9 °C | 18.8 °C | 119.38 mm |
| May | 12.9 °C | 24.1 °C | 127.51 mm |
| June | 17.8 °C | 29.1 °C | 122.17 mm |
| July | 19.6 °C | 30.7 °C | 103.89 mm |
| August | 18.3 °C | 30.2 °C | 90.68 mm |
| September | 13.7 °C | 26.8 °C | 88.9 mm |
| October | 7.3 °C | 20.4 °C | 86.87 mm |
| November | 1.7 °C | 12.3 °C | 99.06 mm |
| December | -2.8 °C | 6 °C | 74.68 mm |
| Annual | 7.3 °C | 18.4 °C | 1149.61 mm |
| 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 : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |