Potomac, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 41.9 °F (low) to 61.9 °F (high). Annual precipitation averages 40.2 Inches. Potomac is located in USDA Plant Hardiness Zone 6a. 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 | 17.8 °F | 33.4 °F | 2.37 in. |
| February | 20.8 °F | 37.9 °F | 2.06 in. |
| March | 30.1 °F | 49.6 °F | 2.77 in. |
| April | 40.7 °F | 63.2 °F | 4.04 in. |
| May | 52.4 °F | 73.9 °F | 4.57 in. |
| June | 61.5 °F | 82.2 °F | 4.73 in. |
| July | 64.2 °F | 84.7 °F | 4.3 in. |
| August | 61.9 °F | 83.3 °F | 3.34 in. |
| September | 54.3 °F | 78.6 °F | 3.16 in. |
| October | 43.0 °F | 66.1 °F | 3.33 in. |
| November | 32.6 °F | 50.9 °F | 3.14 in. |
| December | 23.5 °F | 38.4 °F | 2.36 in. |
| Annual | 41.9 °F | 61.9 °F | 40.17 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 6a : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |