Dundas, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 7.1 °C (low) to 18.3 °C (high). Annual precipitation averages 1160.8 Millimeters. Dundas 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 | -5.5 °C | 3.3 °C | 82.3 mm |
| February | -3.9 °C | 6.1 °C | 62.99 mm |
| March | 0.9 °C | 12 °C | 95.25 mm |
| April | 6.7 °C | 18.7 °C | 123.7 mm |
| May | 12.8 °C | 24.1 °C | 128.02 mm |
| June | 17.7 °C | 28.8 °C | 124.71 mm |
| July | 19.1 °C | 30.6 °C | 113.54 mm |
| August | 17.8 °C | 30.1 °C | 75.44 mm |
| September | 13.4 °C | 27.1 °C | 85.09 mm |
| October | 7.2 °C | 20.4 °C | 90.17 mm |
| November | 1.4 °C | 12.4 °C | 98.81 mm |
| December | -3 °C | 5.8 °C | 80.77 mm |
| Annual | 7.1 °C | 18.3 °C | 1160.79 mm |
| 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 : -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 |