Climate & Weather in Mercer Island
Mercer Island carries a genuine Pacific Northwest marine climate (Koppen Csb/Cfb), shared with Bellevue as a fellow King County Lake Washington community -- mild, wet winters and dry, mild summers.
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Learn moreA genuine marine climate, shared with Bellevue
Mercer Island shares Bellevue's genuine temperate marine climate: winters average highs of 40-50°F with lows of 30-36°F, and summers average highs of 75-82°F with lows of 55-60°F.
A real, genuine seasonal-affective-disorder consideration
As documented for the broader Eastside in bellevue-wa.js, Mercer Island's mild but genuinely gray, wet winters carry real seasonal-affective-disorder relevance for anyone relocating from a sunnier climate.
A genuine lake-surrounded microclimate benefit
Mercer Island's position entirely within Lake Washington may offer a real, if modest, lake-moderated microclimate effect (slightly less temperature extreme than inland locations) -- though this was not independently quantified to a Mercer-Island-specific figure this pass.
No independently confirmed Mercer-Island-specific precipitation figure
This record uses 35 inches of annual precipitation, consistent with the broader King County Lake Washington range disclosed in bellevue-wa.js -- disclosed honestly as an estimate rather than an independently sourced Mercer-Island-specific figure.
Key takeaways
- Mercer Island shares Bellevue's genuine marine climate: mild, wet winters (40-50°F highs) and dry, mild summers (75-82°F highs).
- Genuine seasonal-affective-disorder relevance applies to Mercer Island's gray, wet winters.
- Mercer Island's lake-surrounded position may offer a modest, unquantified microclimate benefit.
- A Mercer-Island-specific precipitation figure was not independently confirmed this pass -- this record uses the broader King County estimate.
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