Oelwein, Iowa has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 36.4 °F (low) to 56.6 °F (high). Annual precipitation averages 37 Inches. Oelwein 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 | 8.3 °F | 25.6 °F | 1.15 in. |
| February | 12.3 °F | 29.8 °F | 1.18 in. |
| March | 24.2 °F | 43.1 °F | 1.89 in. |
| April | 35.6 °F | 57.8 °F | 3.64 in. |
| May | 47.8 °F | 69.6 °F | 4.53 in. |
| June | 58.5 °F | 79.3 °F | 5.62 in. |
| July | 61.6 °F | 82.1 °F | 5.05 in. |
| August | 59.1 °F | 80.1 °F | 4.16 in. |
| September | 50.5 °F | 74.2 °F | 3.7 in. |
| October | 38.1 °F | 61.1 °F | 2.72 in. |
| November | 26.0 °F | 44.7 °F | 1.8 in. |
| December | 15.1 °F | 31.4 °F | 1.55 in. |
| Annual | 36.4 °F | 56.6 °F | 36.99 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 5a : -20°F to -15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |