Winthrop, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 0.8 °C (low) to 15 °C (high). Annual precipitation averages 372.9 Millimeters. Winthrop is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 11 - May 20 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -8.6 °C | -0.6 °C | 51.82 mm |
| February | -7.1 °C | 3.7 °C | 30.99 mm |
| March | -3.3 °C | 9.7 °C | 31.24 mm |
| April | 0.4 °C | 15.9 °C | 21.84 mm |
| May | 4.6 °C | 21.4 °C | 27.18 mm |
| June | 8.1 °C | 24.8 °C | 27.94 mm |
| July | 10.9 °C | 30 °C | 16.51 mm |
| August | 10.3 °C | 30.1 °C | 11.94 mm |
| September | 6 °C | 24.9 °C | 10.92 mm |
| October | 0.7 °C | 15.8 °C | 30.99 mm |
| November | -3.7 °C | 5.4 °C | 50.8 mm |
| December | -8.5 °C | -1.2 °C | 60.71 mm |
| Annual | 0.8 °C | 15 °C | 372.88 mm |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | May 11 - May 20 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |