Humidity in Seattle, Washington Today

Seattle has a temperate marine climate, and that single phrase explains almost everything about its humidity: cool, damp air prevails for much of the year, but the temperature rarely climbs high enough to make that moisture feel oppressive. The Pacific Ocean and Puget Sound act as giant thermal buffers, keeping the air moist but also keeping it cool — so the city runs high relative humidity with relatively low dew points, typically in the 50s°F even in midsummer. It is damp, but not the heavy tropical damp of the Gulf Coast.

The city's famous rain reinforces the pattern without being the main driver. Seattle's precipitation arrives as persistent drizzle rather than intense downpours, spread across roughly 150 wet days a year. Each bout of rain recharges the moisture in the air and on the ground, so the relative humidity rarely dips below 50% even on an August afternoon. When the sun does break through, evaporation off soaked soil and the surrounding water bodies spikes the humidity right back up within hours.

Geography plays a starring role. The Olympic Mountains to the west wring moisture out of Pacific storms before they reach Seattle, and the Cascades to the east trap whatever makes it across. The city sits in the convergence zone between these two ranges, so cloud cover lingers, sunlight is weaker, and the air is rarely baked dry the way it would be in the rain shadow east of the Cascades. The result: Seattle's humidity stays in a narrow, moderate band — high enough to grow moss and ferns, low enough that you rarely hear anyone complain about the mugginess.