Dahlgren, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 45.2 °F (low) to 65.6 °F (high). Annual precipitation averages 45.7 Inches. 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 | 23.0 °F | 39.6 °F | 3.28 in. |
| February | 25.9 °F | 44.5 °F | 2.78 in. |
| March | 34.4 °F | 54.7 °F | 3.95 in. |
| April | 44.5 °F | 66.3 °F | 4.96 in. |
| May | 55.1 °F | 75.4 °F | 5.1 in. |
| June | 63.7 °F | 84.2 °F | 4.68 in. |
| July | 67.1 °F | 87.2 °F | 3.96 in. |
| August | 64.8 °F | 86.5 °F | 3.17 in. |
| September | 56.6 °F | 80.5 °F | 3.17 in. |
| October | 45.0 °F | 68.9 °F | 3.39 in. |
| November | 34.9 °F | 55.0 °F | 4.02 in. |
| December | 27.0 °F | 43.8 °F | 3.22 in. |
| Annual | 45.2 °F | 65.6 °F | 45.68 in. |
| 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 : -5°F to 0°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |