Rosalia, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 2.4 °C (low) to 15.1 °C (high). Annual precipitation averages 463.6 Millimeters. Rosalia is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -3.9 °C | 2.7 °C | 56.39 mm |
| February | -3.3 °C | 5.2 °C | 40.64 mm |
| March | -1.1 °C | 9.6 °C | 47.5 mm |
| April | 1.4 °C | 14.1 °C | 40.64 mm |
| May | 5.1 °C | 19.2 °C | 42.16 mm |
| June | 8.1 °C | 22.6 °C | 34.8 mm |
| July | 10.3 °C | 29.1 °C | 13.72 mm |
| August | 10.1 °C | 29.3 °C | 11.43 mm |
| September | 6.2 °C | 24 °C | 15.49 mm |
| October | 1.8 °C | 15.6 °C | 39.88 mm |
| November | -1.4 °C | 7.1 °C | 59.44 mm |
| December | -4.3 °C | 2.1 °C | 61.47 mm |
| Annual | 2.4 °C | 15.1 °C | 463.56 mm |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 125-150 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |