2025 Compare Climate & Weather:
Portland, OR vs Mercer Island, WA

Highlights

On average, there are 156 sunny days per year in Mercer Island. Portland averages 144 sunny days per year. The US average is 205 sunny days.

Mercer Island, Washington gets 39.2 inches of rain, on average, per year. Portland, Oregon gets 42.8 inches of rain, on average, per year. The US average is 38.1 inches of rain per year.

Mercer Island averages 5.1 inches of snow per year. Portland averages 2.6 inches of snow per year. The US average is 27.8 inches of snow per year.

Weather Highlights

Mercer Island, Washington
Summer High: the July high is around 76 degrees
Winter Low: the January low is 37
Rain: averages 39.2 inches of rain a year
Snow: averages 5.1 inches of snow a year

Portland, Oregon
Summer High: the July high is around 80.5 degrees
Winter Low: the January low is 36.4
Rain: averages 42.8 inches of rain a year
Snow: averages 2.6 inches of snow a year

BestPlaces Comfort Index

The annual BestPlaces Comfort Index for Mercer Island is 7.5 (10=best), which means it is one of the most pleasant places in Washington.

The annual BestPlaces Comfort Index for Portland is 7.5 (10=best), which means it is more comfortable than most places in Oregon.

Today's Weather - Portland, OR

63°F

Today's Weather - Mercer Island, WA

62°F

Average Monthly High / Low (°F)

Hot, Freezing, Rainy, Snowy Days: Portland / Mercer Island

August is the hottest month for Portland with an average high temperature of 81.1°, which ranks it as cooler than most places in Oregon. In Portland, there are 4 comfortable months with high temperatures in the range of 70-85°. The most pleasant months of the year for Portland are September, July and August.

August is the hottest month for Mercer Island with an average high temperature of 76.5°, which ranks it as about average compared to other places in Washington. In Mercer Island, there are 4 comfortable months with high temperatures in the range of 70-85°. The most pleasant months of the year for Mercer Island are August, July and September.

December has the coldest nighttime temperatures for Portland with an average of 35.6°. This is warmer than most places in Oregon.

December has the coldest nighttime temperatures for Mercer Island with an average of 35.7°. This is one of the warmest places in Washington.

In Portland, there are 11.6 days annually when the high temperature is over 90°, which is cooler than most places in Oregon.

In Mercer Island, there are 1.8 days annually when the high temperature is over 90°, which is cooler than most places in Washington.

In Portland, there are 29.2 days annually when the nighttime low temperature falls below freezing, which is warmer than most places in Oregon.

In Mercer Island, there are 25.4 days annually when the nighttime low temperature falls below freezing, which is one of the warmest places in Washington.

In Portland, there are 0.0 days annually when the nighttime low temperature falls below zero°, which is about average compared to other places in Oregon.

In Mercer Island, there are 0.0 days annually when the nighttime low temperature falls below zero°, which is about average compared to other places in Washington.

December is the wettest month in Portland with 6.8 inches of rain, and the driest month is July with 0.7 inches. The wettest season is Spring with 41% of yearly precipitation and 7% occurs in Autumn, which is the driest season. The annual rainfall of 42.8 inches in Portland means that it is about average compared to other places in Oregon.


November is the wettest month in Mercer Island with 6.3 inches of rain, and the driest month is July with 0.9 inches. The wettest season is Spring with 39% of yearly precipitation and 9% occurs in Autumn, which is the driest season. The annual rainfall of 39.2 inches in Mercer Island means that it is about average compared to other places in Washington.

November is the rainiest month in Portland with 19.3 days of rain, and August is the driest month with only 3.7 rainy days. There are 155.9 rainy days annually in Portland, which is rainier than most places in Oregon. The rainiest season is Spring when it rains 34% of the time and the driest is Autumn with only a 11% chance of a rainy day.

November is the rainiest month in Mercer Island with 18.5 days of rain, and August is the driest month with only 5.0 rainy days. There are 152.7 rainy days annually in Mercer Island, which is about average compared to other places in Washington. The rainiest season is Spring when it rains 33% of the time and the driest is Autumn with only a 13% chance of a rainy day.

An annual snowfall of 2.6 inches in Portland means that it is less snowy than most places in Oregon.

An annual snowfall of 5.1 inches in Mercer Island means that it is about average compared to other places in Washington.

December is the snowiest month in Portland with 0.9 inches of snow, and 3 months of the year have significant snowfall.

December is the snowiest month in Mercer Island with 2.2 inches of snow, and 4 months of the year have significant snowfall.