Grass Lake, Michigan has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 38.5 °F (low) to 57.8 °F (high). Annual precipitation averages 35.2 Inches. Grass Lake is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 15.8 °F | 30.8 °F | 2.34 in. |
| February | 16.5 °F | 33.9 °F | 1.92 in. |
| March | 25.0 °F | 44.1 °F | 2.25 in. |
| April | 36.1 °F | 57.3 °F | 3.22 in. |
| May | 47.6 °F | 69.1 °F | 3.85 in. |
| June | 56.6 °F | 78.3 °F | 3.67 in. |
| July | 60.3 °F | 82.2 °F | 3.42 in. |
| August | 58.8 °F | 80.3 °F | 3.51 in. |
| September | 51.4 °F | 74.0 °F | 3.08 in. |
| October | 40.3 °F | 61.0 °F | 3.01 in. |
| November | 30.6 °F | 47.3 °F | 2.67 in. |
| December | 22.4 °F | 35.8 °F | 2.21 in. |
| Annual | 38.5 °F | 57.8 °F | 35.15 in. |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 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 | Dfb - Humid Continental Mild Summer, Wet All Year |