Mountlake Terrace, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.8 °C (low) to 15.1 °C (high). Annual precipitation averages 1049.3 Millimeters. Mountlake Terrace is located in USDA Plant Hardiness Zone 9a. The growing season typically runs from the last frost around Mar. 11 - Mar. 20 through the first frost around Nov. 11 - Nov. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 2.2 °C | 7.9 °C | 140.72 mm |
| February | 2.2 °C | 9.3 °C | 100.33 mm |
| March | 3.6 °C | 11.5 °C | 112.01 mm |
| April | 5.3 °C | 14.1 °C | 87.38 mm |
| May | 8.2 °C | 17.9 °C | 54.1 mm |
| June | 10.3 °C | 20.1 °C | 53.85 mm |
| July | 12.4 °C | 23.5 °C | 23.11 mm |
| August | 12.7 °C | 23.9 °C | 27.69 mm |
| September | 10.8 °C | 20.6 °C | 43.94 mm |
| October | 7.4 °C | 15.1 °C | 101.6 mm |
| November | 3.9 °C | 10.3 °C | 162.31 mm |
| December | 2.1 °C | 7.5 °C | 142.24 mm |
| Annual | 6.8 °C | 15.1 °C | 1049.28 mm |
| Average First Frost Date | Nov. 11 - Nov. 20 |
| Average Last Frost Date | Mar. 11 - Mar. 20 |
| Average Days With Frost | 30-40 Days |
| Plant Hardiness Zone | Zone 9a : -6.7°C to -3.9°C |
| Plant Hardiness Zone - 2012 | Zone 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |