Shannon, Illinois has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 37.8 °F (low) to 57.9 °F (high). Annual precipitation averages 38.2 Inches. Shannon is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 11.9 °F | 28.3 °F | 1.59 in. |
| February | 15.4 °F | 32.6 °F | 1.73 in. |
| March | 25.8 °F | 45.0 °F | 2.23 in. |
| April | 36.3 °F | 58.7 °F | 3.76 in. |
| May | 48.2 °F | 70.3 °F | 4.53 in. |
| June | 58.1 °F | 79.5 °F | 5.23 in. |
| July | 61.4 °F | 82.3 °F | 4.58 in. |
| August | 59.3 °F | 81.0 °F | 3.85 in. |
| September | 50.8 °F | 74.7 °F | 3.69 in. |
| October | 39.7 °F | 61.8 °F | 2.83 in. |
| November | 28.7 °F | 46.4 °F | 2.24 in. |
| December | 18.2 °F | 33.6 °F | 1.94 in. |
| Annual | 37.8 °F | 57.9 °F | 38.2 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |