Mercer Island, WA Weather & Growing Conditions
Local forecast, frost dates, hardiness zone and planting guidance for Mercer Island, a city in King County, Washington.
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 for Mercer Island
| 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) for Mercer Island (47.564, -122.231). Updated through the day.
Growing snapshot for Mercer Island
Last spring frost
Mar 13
First fall frost
Nov 17
Growing season
247 days
Hardiness zone
9a
More local growing data for Mercer Island: nearby ZIP 98040 weather · frost dates · planting calendar · Washington frost dates
Nearby towns & communities
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Baring
Beaux Arts Village
Bellevue
Black Diamond
Bothell
Boulevard Park
Bryn Mawr-Skyway
Burien
Carnation
Clyde Hill
Cottage Lake
Covington
Des Moines
Duvall
East Renton Highlands
Fairwood
Fall City
Federal Way
Greenwater
High Bridge
Hobart
Hunts Point
Index
Issaquah
Kenmore
Kent
Kirkland
Climate data from the nearest NOAA station, Seattle Boeing Fld, Wa (4 mi from Mercer Island). Frost dates are 1991–2020 averages, not a forecast. Page updated Nov 3, 2026.