Watertown, South Dakota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 0.3 °C (low) to 11.9 °C (high). Annual precipitation averages 608.6 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 Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -16.2 °C | -5.8 °C | 17.27 mm |
| February | -14.2 °C | -3.3 °C | 17.02 mm |
| March | -7.4 °C | 3.5 °C | 30.23 mm |
| April | -0.4 °C | 12.2 °C | 58.42 mm |
| May | 6.9 °C | 19.2 °C | 74.17 mm |
| June | 13 °C | 24.7 °C | 96.01 mm |
| July | 15.6 °C | 27.7 °C | 82.04 mm |
| August | 14.1 °C | 26.6 °C | 72.39 mm |
| September | 9.1 °C | 22.2 °C | 66.04 mm |
| October | 1.5 °C | 13.8 °C | 56.64 mm |
| November | -5.9 °C | 4.8 °C | 20.83 mm |
| December | -12.4 °C | -2.8 °C | 17.53 mm |
| Annual | 0.3 °C | 11.9 °C | 608.59 mm |
| 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 4b : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |