| 2023 Hardiness Zone: | Zone 8b: 15°F to 20°F Zone 9a: 20°F to 25°F | |
| 2012 Hardiness Zone: | Zone 8b: 15°F to 20°F | |
| 1990 Hardiness Zone: | Zone 8a: 10F to 15F | |
| Average First Frost Date: | Nov. 11 - Nov. 20 | |
| Average Last Frost Date: | Mar. 21 - Mar. 31 | |
| Koppen-Geiger Climate Zone: | Csb - Warm-Summer Mediterranean Climate | |
| Ecoregion: | 2f - Central Puget Lowland | |
| Current Drought Status: | Exceptional Drought | |
| Heat Zone Days: | Rare Over 86°F |
Annual Climate Data for ZIP Code 98040 - Mercer Island, WA | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Avg Min Temp (°F) | 35 | 36 | 38 | 41 | 47 | 51 | 55 | 55 | 51 | 44 | 39 | 35 | 44 |
| Avg Max Temp (°F) | 46 | 50 | 54 | 59 | 66 | 70 | 76 | 76 | 71 | 61 | 51 | 46 | 61 |
| Avg Precip (In.) | 5.22 | 4.06 | 3.9 | 2.53 | 1.76 | 1.54 | .85 | 1.02 | 1.68 | 3.3 | 5.52 | 5.71 | 37.1 |