Prosser, Washington has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 39.3 °F (low) to 65 °F (high). Annual precipitation averages 8.9 Inches. 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 | 26.6 °F | 40.2 °F | 1.23 in. |
| February | 27.4 °F | 47.6 °F | 0.87 in. |
| March | 31.9 °F | 57.0 °F | 0.72 in. |
| April | 37.0 °F | 65.0 °F | 0.76 in. |
| May | 45.4 °F | 74.4 °F | 0.67 in. |
| June | 51.2 °F | 81.2 °F | 0.68 in. |
| July | 55.5 °F | 90.3 °F | 0.42 in. |
| August | 54.6 °F | 89.2 °F | 0.22 in. |
| September | 47.1 °F | 79.8 °F | 0.3 in. |
| October | 38.2 °F | 65.4 °F | 0.86 in. |
| November | 30.3 °F | 50.1 °F | 0.94 in. |
| December | 26.1 °F | 40.1 °F | 1.21 in. |
| Annual | 39.3 °F | 65 °F | 8.88 in. |
| 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 : 5°F to 10°F |
| Plant Hardiness Zone - 2012 | Zone 7a : 0°F to 5°F |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |