Royal City, Washington has a Cold Desert Climate climate (Köppen classification: BWk). Average annual temperatures range from 4.6 °C (low) to 17.1 °C (high). Annual precipitation averages 194.3 Millimeters. Royal City is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -3.7 °C | 3.2 °C | 25.91 mm |
| February | -2.2 °C | 7.2 °C | 16.76 mm |
| March | 0.5 °C | 12.6 °C | 17.53 mm |
| April | 3.6 °C | 17.2 °C | 16 mm |
| May | 7.8 °C | 22.3 °C | 13.97 mm |
| June | 11.1 °C | 25.9 °C | 16.76 mm |
| July | 14.5 °C | 31 °C | 9.65 mm |
| August | 14.1 °C | 30.6 °C | 4.32 mm |
| September | 9.7 °C | 25.7 °C | 5.59 mm |
| October | 4.2 °C | 17.6 °C | 16.51 mm |
| November | -0.7 °C | 8.7 °C | 22.86 mm |
| December | -3.9 °C | 2.8 °C | 28.45 mm |
| Annual | 4.6 °C | 17.1 °C | 194.31 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 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 | BWk - Cold Desert Climate |