Mercer Island, Washington Weather
Rufous Hummingbirds Arrive. Day 76 of spring. Read this microseason across nine climate regions →
Mercer Island weather forecast — hour by hour, 7-day outlook, NOAA radar
- TodayJun 3Overcast14%—71°57°—
- ThursdayJun 4Overcast11%—65°52°-6°
- FridayJun 5Drizzle51%—61°49°-4°
- SaturdayJun 6Light Showers80%—55°45°-6°
- SundayJun 7Light Drizzle——66°46°+11°
- MondayJun 8Light Drizzle53%0.12″54°49°-12°
- TuesdayJun 9Light Drizzle44%—64°48°+10°
Ozone at AQI 47 — peak already passed at 1 PM under overcast skies. AQI flat over the last 6 hours (within ±3 points). Levels should ease through evening.
OK No precautions needed for the general population; unusually sensitive individuals may consider limiting prolonged outdoor exertion.
What's driving it
Ozone × UV × Sky
Ozone at AQI 47 — peak already passed at 1 PM under overcast skies. Levels should ease through evening.
- Present
- AQI 47
- UV peak
- 3.0 at earlier today
- Sky at peak
- overcast
- Projected peak
- AQI 47
PM × Wind × Precip
PM2.5/PM10 ratio 0.63 with 9 mph wind — characteristic of long-range haze transport rather than a local source.
- PM2.5/PM10
- 0.63
- Wind
- light
- Recent rain
- 0h in last 6h
- Pattern
- transport
Trends
Seven days of AQI and PM2.5.
Hourly air-quality data from the Copernicus Atmosphere Monitoring Service, charted across the past and next several days. Dashed lines mark the AQI breakpoints at 50 (Good → Moderate) and 100 (Moderate → Unhealthy for Sensitive Groups).
The higher the clouds, the finer the weather.
- Moonrise
- 6:38 AM
- Moonset
- 2:41 PM
- In sign
- ♑︎ Capricorn
Rufous Hummingbirds Arrive
Mercer Island at a glance
- Today vs. normal: 69°F — typical for the season
- Last frost: May 31 (climatological average for this latitude)
- Microseason: Jun 1–5
- Planting window: Harvest spring lettuce before it bolts. Sow heat-tolerant greens.
Right now in the garden
Peak growing season
As of June 3, the growing season is at its peak — frost is months away. Continue succession-planting beans and summer squash. Start fall brassicas (broccoli, cabbage, kale) from seed indoors for transplanting in late summer.
SPC Convective Outlook
Storm Prediction Center — Mercer Island
SPC has placed Mercer Island in the General Thunderstorms category for severe thunderstorms day after tomorrow.
- TODAYNONENo severe risk
- TOMORROWNONENo severe risk
- DAY 3TSTMGeneral Thunderstorms
Thunderstorms possible. Not severe, but capable of producing lightning and brief heavy rain.
Source: NOAA / NWS Storm Prediction Center categorical convective outlook. Outlooks are re-issued multiple times per day; this page reflects the most recent SPC polygons covering the city’s coordinates.
Planting calendar
| Month | Plant | Harvest |
|---|---|---|
| January | — | — |
| February | — | — |
| March | — | — |
| April | — | — |
| May | lettuce, peas, spinach, radishes | lettuce, peas, radishes |
| June | lettuce, peas, spinach, radishes, tomatoes, peppers, beans, squash | lettuce, peas, radishes |
| July | tomatoes, peppers, beans, squash | tomatoes, beans, summer squash |
| August | tomatoes, peppers, beans, squash, fall brassicas, garlic (overwinter), carrots | tomatoes, beans, summer squash |
| September | fall brassicas, garlic (overwinter), carrots | tomatoes, beans, summer squash |
| October | — | winter squash, tomatoes (last) |
| November | — | — |
| December | — | — |
A year in weather
Mercer Island's warmest month is August (~67°F mean) and its coldest is December (~42°F). Rainfall peaks in November (5.8 inches) and bottoms out in July (0.8 inches).
| Month | Mean temp | Precip | Rainy days |
|---|---|---|---|
| January | 42° | 5.1″ | 12 |
| February | 43° | 3.5″ | 9 |
| March | 47° | 3.9″ | 11 |
| April | 51° | 3.0″ | 9 |
| May | 57° | 2.2″ | 6 |
| June | 61° | 1.6″ | 5 |
| July | 67° | 0.8″ | 2 |
| August | 67° | 1.0″ | 3 |
| September | 62° | 1.7″ | 5 |
| October | 54° | 3.6″ | 9 |
| November | 46° | 5.8″ | 12 |
| December | 42° | 5.5″ | 12 |
Regional context
Mercer Island sits within a warm-summer Mediterranean climate region — a cohort that shares similar temperature ranges, seasonal patterns, and growing conditions across nearby cities.
Similar climates: Seattle, WA, Spokane, WA, Kennewick, WA, Bremerton, WA, Tacoma, WA.
Frequently asked
- When does it freeze in Mercer Island?
- Mercer Island's last spring frost typically falls around mid-May, and the first fall frost arrives around mid-October.
- What is the rainy season in Mercer Island?
- November is the wettest month with about 5.8 inches of rain on average; the city receives roughly 38 inches annually.
- What is the warmest month in Mercer Island?
- August is typically warmest, averaging about 67°F.
- What is the coldest month in Mercer Island?
- December is typically coldest, averaging about 42°F.
- When can I start a vegetable garden in Mercer Island?
- Cool-season crops (peas, lettuce) can be sown around the last spring frost (mid-May); warm-season crops (tomatoes, peppers) wait until 1–2 weeks after.
- How many rainy days does Mercer Island get?
- Mercer Island averages about 95 rainy days per year.
- What hardiness zone is Mercer Island?
- Mercer Island's USDA hardiness zone is determined by its lowest average winter temperature; check the USDA's online lookup with the city ZIP for the current zone designation.
Climate
Mercer Island, Washington sits in a warm-summer Mediterranean climate zone. January means hover near 42°F while July averages 67°F — a 24°F seasonal swing.
Across the year, Mercer Island receives about 38 inches of precipitation spread over roughly 95 rainy days.
The rhythm of the year is set by latitude (47.6°N), proximity to large water bodies, and elevation — all of which shape what grows here, when frost is likely, and what the weather story looks like day to day.