Ever heard of the Puget Sound Convergence zone? It's Seattle's version of Lake effect snow.
The Pacific Low pressure weather systems come in off the Pacific, and when they reach the Olympic Mountains, tend to split. Some energy ends up entering around Everett WA and some runs in over the Olympia WA area. It's difficult to forecast how much energy will go in which direction but they tend to "converge" in the Seattle/Tacoma areas, hence the drizzle & fog. Olympia gets much more fog than Seattle because of their location relative to the Olympics. Frequently this convergence is accompanied by temperature inversions. That causes all the pollution/fog/smoke etc. to get trapped between the ground and the base of the system. When that happens, mostly winter, December is worst, they cam have fog for weeks at a time. Always seems to hit around the Thanksgiving and Christmas seasons causing problems with the holiday travel. During the temp. inversions King County has a "burn ban." When that's in effect you can't use your wood burning fireplace unless it's your only source of heat. Get caught, get fined $$.
Washington is not called the Evergreen State for nothing. Everything gets plenty of precip., much more frequently during all the seasons except Summer. It's evergreen between the coast and the Cascade Mountains. E of the mountains it's mostly dry high desert till you get to the Idaho panhandle.
Can't comment on Portland, never lived there. Balderdash????