Postville, Iowa has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 35.7 °F (low) to 55.8 °F (high). Annual precipitation averages 38.8 Inches. Postville is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 7.7 °F | 24.8 °F | 1.08 in. |
| February | 11.0 °F | 29.3 °F | 1.19 in. |
| March | 23.2 °F | 42.3 °F | 2.25 in. |
| April | 34.7 °F | 56.8 °F | 4.15 in. |
| May | 46.6 °F | 68.8 °F | 4.98 in. |
| June | 57.6 °F | 78.5 °F | 5.85 in. |
| July | 60.9 °F | 81.7 °F | 4.63 in. |
| August | 58.3 °F | 79.9 °F | 4.26 in. |
| September | 49.9 °F | 73.2 °F | 3.95 in. |
| October | 37.6 °F | 60.2 °F | 2.95 in. |
| November | 25.9 °F | 43.7 °F | 2.0 in. |
| December | 14.6 °F | 30.6 °F | 1.48 in. |
| Annual | 35.7 °F | 55.8 °F | 38.77 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |