Winthrop, Washington has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 33.5 °F (low) to 59 °F (high). Annual precipitation averages 14.7 Inches. 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 | 16.6 °F | 31.0 °F | 2.04 in. |
| February | 19.3 °F | 38.7 °F | 1.22 in. |
| March | 26.0 °F | 49.5 °F | 1.23 in. |
| April | 32.7 °F | 60.6 °F | 0.86 in. |
| May | 40.2 °F | 70.6 °F | 1.07 in. |
| June | 46.5 °F | 76.6 °F | 1.1 in. |
| July | 51.7 °F | 86.0 °F | 0.65 in. |
| August | 50.6 °F | 86.1 °F | 0.47 in. |
| September | 42.8 °F | 76.9 °F | 0.43 in. |
| October | 33.3 °F | 60.5 °F | 1.22 in. |
| November | 25.4 °F | 41.8 °F | 2.0 in. |
| December | 16.7 °F | 29.8 °F | 2.39 in. |
| Annual | 33.5 °F | 59 °F | 14.68 in. |
| 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 : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |