Posen, Michigan has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.1 °C (low) to 12.1 °C (high). Annual precipitation averages 811 Millimeters. Posen is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -11.4 °C | -3.1 °C | 47.75 mm |
| February | -12 °C | -1.7 °C | 36.83 mm |
| March | -7.8 °C | 3.6 °C | 44.96 mm |
| April | -1.2 °C | 10.6 °C | 78.23 mm |
| May | 5.2 °C | 18.2 °C | 77.47 mm |
| June | 10.5 °C | 23.8 °C | 78.49 mm |
| July | 13.4 °C | 26.1 °C | 79.5 mm |
| August | 12.9 °C | 25.6 °C | 83.06 mm |
| September | 9.2 °C | 21.6 °C | 73.66 mm |
| October | 3.2 °C | 13.7 °C | 87.63 mm |
| November | -2 °C | 6.3 °C | 67.31 mm |
| December | -7.1 °C | 0.2 °C | 56.13 mm |
| Annual | 1.1 °C | 12.1 °C | 811.02 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |