Brethren, Michigan has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.1 °C (low) to 13.2 °C (high). Annual precipitation averages 920.2 Millimeters. Brethren is located in USDA Plant Hardiness Zone 5b. 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 | -9.4 °C | -1.7 °C | 61.21 mm |
| February | -9.6 °C | -0.1 °C | 45.97 mm |
| March | -6 °C | 5.3 °C | 55.88 mm |
| April | 0 °C | 12.6 °C | 86.11 mm |
| May | 6.1 °C | 19.8 °C | 89.41 mm |
| June | 11.4 °C | 24.9 °C | 87.12 mm |
| July | 13.7 °C | 27 °C | 81.28 mm |
| August | 13 °C | 25.9 °C | 77.47 mm |
| September | 9.2 °C | 22.1 °C | 84.58 mm |
| October | 3.4 °C | 14.6 °C | 105.92 mm |
| November | -1.3 °C | 7 °C | 80.26 mm |
| December | -5.8 °C | 1.1 °C | 65.02 mm |
| Annual | 2.1 °C | 13.2 °C | 920.23 mm |
| 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 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |