Posen, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 5.7 °C (low) to 15.5 °C (high). Annual precipitation averages 1010.7 Millimeters. Posen is located in USDA Plant Hardiness Zone 6a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -7.9 °C | 0.1 °C | 55.63 mm |
| February | -6.4 °C | 2.1 °C | 52.83 mm |
| March | -1.3 °C | 8.2 °C | 60.45 mm |
| April | 4.3 °C | 15.3 °C | 99.06 mm |
| May | 10.4 °C | 21.3 °C | 115.57 mm |
| June | 16 °C | 26.8 °C | 113.03 mm |
| July | 18.7 °C | 29.1 °C | 111.76 mm |
| August | 17.7 °C | 28.1 °C | 106.17 mm |
| September | 13.6 °C | 24.7 °C | 82.3 mm |
| October | 6.8 °C | 17.4 °C | 88.14 mm |
| November | 0.8 °C | 9.6 °C | 67.82 mm |
| December | -4.8 °C | 2.9 °C | 57.91 mm |
| Annual | 5.7 °C | 15.5 °C | 1010.67 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6a : -23.3°C to -20.6°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |