An oceanic climate (also called "west coast marine climate") predominates in western Washington, and a much drier semi-arid climate prevails east of the Cascade Range.
Major factors determining Washington's climate include the large semi-permanent high pressure and low pressure systems of the north Pacific Ocean, the continental air masses of North America, and the Olympic and Cascade mountains.
The term "Pineapple Express" is used colloquially to describe the extreme form of the wet-season Chinook winds.
Despite western Washington's having a marine climate similar to many coastal cities of Europe, there are exceptions such as the "Big Snow" events of 1880, 1881, 1893, and 1916, and the "deep freeze" winters of 1883–1884, 1915–1916, 1949–1950, and 1955–1956, among others.
In the spring and summer, a high pressure anticyclone system dominates the north Pacific Ocean, causing air to spiral out in a clockwise fashion.