Why is Seattle so rainy?
From fall through spring, a steady parade of storms rolls in off the Pacific and gets lifted by the Olympic Mountains and the Cascades. Seattle gets light rain on around 150 days a year, yet it gets less total rain than New York City. It's frequent, not heavy.
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The storm track
In the cool season the jet stream points straight at the Pacific Northwest, steering one ocean storm after another ashore. The air is mild and damp from crossing thousands of miles of ocean, so clouds and drizzle are the default from October to April.
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Mountains on both sides
The Olympic Mountains wring out the heaviest rain on their western slopes, where the Hoh Rain Forest gets around 140 inches a year. Seattle sits partly in their shadow, so its rain comes as frequent light drizzle, around 38 inches a year. The Cascades then lift the air again, piling snow on the passes and leaving eastern Washington dry.
Dry summers
In summer the storm track shifts north and high pressure builds offshore, so July and August are often among the driest, sunniest months on the West Coast.
Questions people ask
- Is Seattle the rainiest city in the US?
- Not by total amount. Many East Coast and Gulf Coast cities get more rain; Seattle just has more cloudy, drizzly days.
- Why is eastern Washington so dry?
- It's in the rain shadow of the Cascades, which squeeze most of the Pacific moisture out of the air first.