Northport, Washington has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 3 °C (low) to 15.3 °C (high). Annual precipitation averages 520.4 Millimeters. Northport is located in USDA Plant Hardiness Zone 6b. 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 | -4.2 °C | 0.8 °C | 56.9 mm |
| February | -3.8 °C | 4.3 °C | 36.32 mm |
| March | -1.2 °C | 10.1 °C | 43.94 mm |
| April | 1.7 °C | 16.1 °C | 40.89 mm |
| May | 6.2 °C | 21.6 °C | 52.58 mm |
| June | 9.3 °C | 24.6 °C | 62.23 mm |
| July | 11.8 °C | 30.2 °C | 26.92 mm |
| August | 11.4 °C | 30.6 °C | 16.76 mm |
| September | 7.6 °C | 24.4 °C | 24.64 mm |
| October | 2.4 °C | 14.8 °C | 39.12 mm |
| November | -0.8 °C | 5.8 °C | 60.2 mm |
| December | -4.2 °C | 0.8 °C | 59.94 mm |
| Annual | 3 °C | 15.3 °C | 520.44 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 | Dfb - Humid Continental Mild Summer, Wet All Year |