Prosser, Washington has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 4 °C (low) to 18.4 °C (high). Annual precipitation averages 225.6 Millimeters. Prosser is located in USDA Plant Hardiness Zone 7b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -3 °C | 4.6 °C | 31.24 mm |
| February | -2.6 °C | 8.7 °C | 22.1 mm |
| March | -0.1 °C | 13.9 °C | 18.29 mm |
| April | 2.8 °C | 18.3 °C | 19.3 mm |
| May | 7.4 °C | 23.6 °C | 17.02 mm |
| June | 10.7 °C | 27.3 °C | 17.27 mm |
| July | 13.1 °C | 32.4 °C | 10.67 mm |
| August | 12.6 °C | 31.8 °C | 5.59 mm |
| September | 8.4 °C | 26.6 °C | 7.62 mm |
| October | 3.4 °C | 18.6 °C | 21.84 mm |
| November | -0.9 °C | 10.1 °C | 23.88 mm |
| December | -3.3 °C | 4.5 °C | 30.73 mm |
| Annual | 4 °C | 18.4 °C | 225.55 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 7b : -15°C to -12.2°C |
| Plant Hardiness Zone - 2012 | Zone 7a : -17.8°C to -15°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |