Inchelium, Washington has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 2.3 °C (low) to 15.9 °C (high). Annual precipitation averages 436.6 Millimeters. Inchelium is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.9 °C | 1.4 °C | 51.82 mm |
| February | -4.7 °C | 4.8 °C | 38.1 mm |
| March | -1.7 °C | 10.7 °C | 46.99 mm |
| April | 1.2 °C | 16.3 °C | 33.53 mm |
| May | 5.4 °C | 21.9 °C | 35.81 mm |
| June | 8.6 °C | 25.1 °C | 30.48 mm |
| July | 11.1 °C | 30.8 °C | 15.75 mm |
| August | 10.4 °C | 30.8 °C | 10.41 mm |
| September | 6.6 °C | 25.1 °C | 16.51 mm |
| October | 1.8 °C | 15.6 °C | 37.34 mm |
| November | -1.6 °C | 6.5 °C | 52.32 mm |
| December | -4.9 °C | 1.4 °C | 67.56 mm |
| Annual | 2.3 °C | 15.9 °C | 436.62 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6a : -23.3°C to -20.6°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |