Harrietta, Michigan has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.3 °C (low) to 12.7 °C (high). Annual precipitation averages 924.3 Millimeters. Harrietta is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -10.9 °C | -2.7 °C | 61.21 mm |
| February | -11.1 °C | -1.1 °C | 45.72 mm |
| March | -7.1 °C | 4.7 °C | 54.61 mm |
| April | -0.8 °C | 12 °C | 86.36 mm |
| May | 5.7 °C | 19.4 °C | 89.41 mm |
| June | 11.1 °C | 24.7 °C | 90.17 mm |
| July | 13.3 °C | 26.8 °C | 83.57 mm |
| August | 12.7 °C | 25.8 °C | 83.82 mm |
| September | 8.6 °C | 21.7 °C | 84.84 mm |
| October | 2.9 °C | 14.1 °C | 103.63 mm |
| November | -2.2 °C | 6.3 °C | 77.98 mm |
| December | -6.9 °C | 0.2 °C | 62.99 mm |
| Annual | 1.3 °C | 12.7 °C | 924.31 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |