Watertown, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2 °C (low) to 12.3 °C (high). Annual precipitation averages 804.4 Millimeters. Watertown is located in USDA Plant Hardiness Zone 4b. 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 | -14.9 °C | -5.3 °C | 20.57 mm |
| February | -13 °C | -2.7 °C | 21.59 mm |
| March | -5.9 °C | 4.3 °C | 37.34 mm |
| April | 1.6 °C | 12.7 °C | 72.64 mm |
| May | 8.7 °C | 19.9 °C | 108.46 mm |
| June | 14.6 °C | 25.3 °C | 122.43 mm |
| July | 16.9 °C | 27.8 °C | 100.84 mm |
| August | 15.6 °C | 26.5 °C | 109.47 mm |
| September | 10.9 °C | 22.4 °C | 82.8 mm |
| October | 3.6 °C | 14.3 °C | 60.71 mm |
| November | -3.6 °C | 5.3 °C | 38.1 mm |
| December | -10.9 °C | -2.4 °C | 29.46 mm |
| Annual | 2 °C | 12.3 °C | 804.41 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 4b : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |