Posen, Illinois has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 42.2 °F (low) to 59.9 °F (high). Annual precipitation averages 39.8 Inches. 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 | 17.7 °F | 32.2 °F | 2.19 in. |
| February | 20.4 °F | 35.8 °F | 2.08 in. |
| March | 29.6 °F | 46.7 °F | 2.38 in. |
| April | 39.8 °F | 59.5 °F | 3.9 in. |
| May | 50.7 °F | 70.4 °F | 4.55 in. |
| June | 60.8 °F | 80.3 °F | 4.45 in. |
| July | 65.6 °F | 84.4 °F | 4.4 in. |
| August | 63.9 °F | 82.6 °F | 4.18 in. |
| September | 56.5 °F | 76.4 °F | 3.24 in. |
| October | 44.2 °F | 63.4 °F | 3.47 in. |
| November | 33.4 °F | 49.2 °F | 2.67 in. |
| December | 23.4 °F | 37.3 °F | 2.28 in. |
| Annual | 42.2 °F | 59.9 °F | 39.79 in. |
| 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 : -10°F to -5°F |
| Plant Hardiness Zone - 2012 | Zone 6a : -10°F to -5°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |