Weather in Mercer Island, Washington
Shoots and Sprouts Rise in Ranks. Day 58 of spring. Read this microseason across nine climate regions →
- TodayMay 16Light Drizzle40%56°45°
- SundayMay 17Overcast—63°41°
- MondayMay 18Overcast—67°48°
- TuesdayMay 19Light Drizzle—64°50°
- WednesdayMay 20Overcast—68°46°
- ThursdayMay 21Mostly Clear—77°48°
- FridayMay 22Overcast—74°52°
- PM 2.5
- 3.2 μg/m³
- PM 10
- 3.7 μg/m³
- NO₂
- 4.6 μg/m³
- Ozone
- 78.0 μg/m³
- UV Index
- 2.1 Low
Flowers blooming in late autumn, a sure sign of a bad winter coming.
- Moonrise
- 11:50 AM
- Moonset
- 3:04 AM
- In sign
- ♉︎ Taurus
Shoots and Sprouts Rise in Ranks
Mercer Island at a glance
- Today vs. normal: 8°F below the seasonal normal for this latitude
- Last frost: May 31 (climatological average for this latitude)
- Microseason: 28 of 72, May 16–20
- Planting window: Direct sow okra, melons, and southern peas. Thin carrot rows.
Right now in the garden
Cool-season window is open
As of May 16, the cool-season window is open or about to open. Direct-sow peas, lettuce, spinach, radishes, and brassicas now. Hold off on warm-season crops until 1–2 weeks after the last spring frost (around May).
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.