Roslyn, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 2 °C (low) to 12.9 °C (high). Annual precipitation averages 1075.7 Millimeters. Roslyn is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.4 °C | 1.5 °C | 174.75 mm |
| February | -4.4 °C | 4.2 °C | 124.46 mm |
| March | -2.4 °C | 7.8 °C | 92.46 mm |
| April | 0.3 °C | 11.8 °C | 57.4 mm |
| May | 4.2 °C | 16.7 °C | 45.47 mm |
| June | 7.8 °C | 19.9 °C | 29.72 mm |
| July | 10.9 °C | 25.2 °C | 15.75 mm |
| August | 10.5 °C | 25.8 °C | 12.45 mm |
| September | 6.3 °C | 21.4 °C | 34.54 mm |
| October | 1.7 °C | 13.5 °C | 112.01 mm |
| November | -2 °C | 5.6 °C | 169.42 mm |
| December | -4.7 °C | 1.2 °C | 207.26 mm |
| Annual | 2 °C | 12.9 °C | 1075.69 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°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 |