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
81°F
Sunny then Areas Of Smoke
Areas of smoke after noon. Sunny, with a high near 81. North wind 5 to 8 mph.
7-day forecast for Mercer Island
| When | Temp | Forecast | Wind | Precip |
|---|---|---|---|---|
| Today | 81°F | Sunny then Areas Of Smoke | 5 to 8 mph N | 0% |
| Tonight | 60°F | Areas Of Smoke | 3 to 8 mph NNE | 0% |
| Wednesday | 86°F | Patchy Smoke | 3 to 7 mph N | 0% |
| Wednesday Night | 62°F | Mostly Clear | 1 to 7 mph NNE | 0% |
| Thursday | 86°F | Sunny | 1 to 6 mph NW | 0% |
| Thursday Night | 63°F | Mostly Clear | 2 to 6 mph W | 0% |
| Friday | 87°F | Sunny | 5 mph SW | 0% |
| Friday Night | 62°F | Mostly Clear | 1 to 6 mph NNE | 0% |
| Saturday | 84°F | Sunny | 1 to 6 mph WNW | 0% |
| Saturday Night | 60°F | Mostly Clear | 2 to 8 mph NNE | 1% |
| Sunday | 79°F | Mostly Sunny | 3 mph WSW | 1% |
| Sunday Night | 59°F | Mostly Clear | 3 mph NNE | 1% |
| Monday | 78°F | Mostly Sunny | 5 mph WNW | 1% |
| Monday Night | 59°F | Partly Cloudy | 5 mph NNE | 0% |
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
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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 Aug 4, 2026.