Mercer Island, WA Weather & Growing Conditions
Today
71°F
Partly Sunny
Partly sunny, with a high near 71. West southwest wind around 2 mph.
7-day forecast
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Today | 71°F | Partly Sunny | 2 mph WSW | 0% |
| Tonight | 56°F | Mostly Clear | 3 mph N | 0% |
| Sunday | 71°F | Mostly Sunny | 5 mph N | 0% |
| Sunday Night | 55°F | Mostly Clear | 5 mph NNE | 0% |
| Monday | 70°F | Mostly Sunny | 3 mph N | 0% |
| Monday Night | 56°F | Partly Cloudy | 3 mph NNE | 1% |
| Tuesday | 68°F | Partly Sunny | 2 mph N | 1% |
| Tuesday Night | 54°F | Mostly Cloudy | 2 mph E | 8% |
| Wednesday | 69°F | Partly Sunny then Slight Chance Light Rain | 3 mph SW | 16% |
| Wednesday Night | 54°F | Slight Chance Light Rain then Mostly Cloudy | 3 mph NNE | 16% |
| Thursday | 66°F | Mostly Cloudy then Slight Chance Light Rain | 2 to 6 mph NNE | 21% |
| Thursday Night | 53°F | Slight Chance Light Rain | 2 to 6 mph NNE | 21% |
| Friday | 65°F | Slight Chance Light Rain | 2 to 6 mph N | 15% |
| Friday Night | 51°F | Slight Chance Light Rain then Partly Cloudy | 5 mph NNE | 15% |
Forecast source: National Weather Service (api.weather.gov). Updated through the day.
Growing snapshot for Mercer Island, WA
Last spring frost
Mar 13
First fall frost
Nov 17
Growing season
247 days
Hardiness zone
9a
Explore more for Mercer Island, WA: full frost dates · planting calendar · Washington frost dates
Climate data from the nearest NOAA station, Seattle Boeing Fld, Wa (4 mi). Frost dates are 1991–2020 averages, not a forecast. Page updated Sep 19, 2026.