Mason, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 6.9 °C (low) to 18.1 °C (high). Annual precipitation averages 1127 Millimeters. Mason 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 | -5.9 °C | 3.1 °C | 76.2 mm |
| February | -4.2 °C | 5.7 °C | 63.25 mm |
| March | 0.8 °C | 11.7 °C | 86.87 mm |
| April | 6.5 °C | 18.6 °C | 122.68 mm |
| May | 12.5 °C | 24 °C | 125.98 mm |
| June | 17.5 °C | 28.9 °C | 125.22 mm |
| July | 19.1 °C | 30.7 °C | 107.44 mm |
| August | 17.8 °C | 30.1 °C | 79.25 mm |
| September | 13.2 °C | 26.8 °C | 81.28 mm |
| October | 6.9 °C | 20.2 °C | 87.88 mm |
| November | 1.3 °C | 12.1 °C | 96.77 mm |
| December | -3.2 °C | 5.6 °C | 74.17 mm |
| Annual | 6.9 °C | 18.1 °C | 1126.99 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 |