Mainly because the Juan de Fuca plate is subducting beneath the North American plate, giving rise to the Cascade mountains farther inland. Those mountains give warm moister rich air coming in from the pacific no where to go but up, which causes the air to cool. The lower energy of cool air means less water can stay in vapor form, so the moisture condenses into rain clouds. This is especially true in the winter when changing air pressure patterns bring nearly constant stream of of moist air over the region, which promptly gets squeezed out, giving us winters with gray skies but lush greenery everywhere else. That’s also why there the area immediately to the east of the cascades is so dry, with the moisture slready being forced out of the air.
The subducting plate has to go deep enough to melt in order to give off enough steam etc to push up mountains, that’s why there is often a flatter area (called a forearc basin) between the coast and subduction mountain ranges. These flat areas benefit from all of that rain and remitted good area for growing things, like the Willamette Valley. You see this pattern in many places around the world, including California where there is the coast, the Central Valley (forarc basin), and then the Sierra Nevadas. Also western Chile.
2
u/One_Competition_8459 3d ago
Why does the north west have so much beautiful greenery