Onamia, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 30.9 °F (low) to 51.6 °F (high). Annual precipitation averages 30.2 Inches. Onamia is located in USDA Plant Hardiness Zone 4a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -0.5 °F | 19.5 °F | 0.67 in. |
| February | 3.0 °F | 25.2 °F | 0.78 in. |
| March | 16.1 °F | 37.7 °F | 1.42 in. |
| April | 30.1 °F | 51.8 °F | 2.53 in. |
| May | 43.0 °F | 65.5 °F | 3.59 in. |
| June | 53.5 °F | 74.9 °F | 4.55 in. |
| July | 57.6 °F | 79.5 °F | 4.42 in. |
| August | 55.1 °F | 77.4 °F | 3.93 in. |
| September | 47.1 °F | 69.3 °F | 2.98 in. |
| October | 35.1 °F | 54.7 °F | 2.93 in. |
| November | 22.1 °F | 38.5 °F | 1.43 in. |
| December | 8.8 °F | 25.0 °F | 0.99 in. |
| Annual | 30.9 °F | 51.6 °F | 30.22 in. |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4a : -30°F to -25°F |
| Plant Hardiness Zone - 2012 | Zone 3b : -35°F to -30°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |