Lena, Illinois has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3.1 °C (low) to 14.1 °C (high). Annual precipitation averages 960.4 Millimeters. Lena is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.5 °C | -2.3 °C | 35.81 mm |
| February | -9.6 °C | 0.1 °C | 40.13 mm |
| March | -3.7 °C | 6.9 °C | 52.58 mm |
| April | 2.3 °C | 14.6 °C | 94.74 mm |
| May | 8.8 °C | 21 °C | 108.71 mm |
| June | 14.4 °C | 26.2 °C | 140.72 mm |
| July | 16.3 °C | 27.8 °C | 112.52 mm |
| August | 15.2 °C | 26.9 °C | 101.85 mm |
| September | 10.5 °C | 23.4 °C | 96.01 mm |
| October | 4.2 °C | 16.3 °C | 74.68 mm |
| November | -1.9 °C | 7.8 °C | 57.4 mm |
| December | -7.9 °C | 0.7 °C | 45.21 mm |
| Annual | 3.1 °C | 14.1 °C | 960.36 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |