Mercer Island, WA Weather & Growing Conditions
Today
57°F
Mostly Cloudy
Mostly cloudy. High near 57, with temperatures falling to around 55 in the afternoon. North northwest wind around 3 mph.
7-day forecast
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Today | 57°F | Mostly Cloudy | 3 mph NNW | 4% |
| Tonight | 46°F | Partly Cloudy | 2 mph ESE | 3% |
| Wednesday | 58°F | Mostly Sunny then Slight Chance Light Rain | 3 mph S | 15% |
| Wednesday Night | 52°F | Light Rain | 3 to 13 mph S | 91% |
| Thursday | 58°F | Slight Chance Light Rain then Partly Sunny | 5 to 10 mph SSW | 18% |
| Thursday Night | 51°F | Light Rain | 5 to 9 mph S | 77% |
| Friday | 57°F | Light Rain | 5 to 10 mph S | 77% |
| Friday Night | 49°F | Chance Light Rain | 5 mph SSE | 48% |
| Saturday | 62°F | Chance Light Rain | 3 mph S | 30% |
| Saturday Night | 52°F | Light Rain Likely | 3 to 15 mph S | 71% |
| Sunday | 58°F | Light Rain Likely | 3 to 15 mph SSW | 70% |
| Sunday Night | 47°F | Slight Chance Light Rain | 3 mph SE | 21% |
| Monday | 57°F | Chance Light Rain | 3 mph SE | 52% |
| Monday Night | 49°F | Light Rain Likely | 3 to 8 mph SSE | 70% |
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 Nov 4, 2026.