Dahlgren, 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 18.6 °C (high). Annual precipitation averages 1160.3 Millimeters. Dahlgren is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5 °C | 4.2 °C | 83.31 mm |
| February | -3.4 °C | 6.9 °C | 70.61 mm |
| March | 1.3 °C | 12.6 °C | 100.33 mm |
| April | 6.9 °C | 19.1 °C | 125.98 mm |
| May | 12.8 °C | 24.1 °C | 129.54 mm |
| June | 17.6 °C | 29 °C | 118.87 mm |
| July | 19.5 °C | 30.7 °C | 100.58 mm |
| August | 18.2 °C | 30.3 °C | 80.52 mm |
| September | 13.7 °C | 26.9 °C | 80.52 mm |
| October | 7.2 °C | 20.5 °C | 86.11 mm |
| November | 1.6 °C | 12.8 °C | 102.11 mm |
| December | -2.8 °C | 6.6 °C | 81.79 mm |
| Annual | 7.3 °C | 18.6 °C | 1160.27 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |