I haven’t spent enough time up in the Pacific Northwest to say for sure. Probably a bit later up there than CA. But even though cities like Seattle and Vancouver are very far north on paper, the low elevation and vicinity to the ocean are enough that snow or freezing temps are like, pretty unusual - the main push of spring migration is later, more similar to the east, because it’s still winter in the mountains - but breeding activities in coastal lowlands can start very early. California Thrashers will start nesting in November, and Anna’s Hummingbirds and Great Horned Owls will start in December/January. Allen’s Hummingbirds are one of our first spring migrants and start arriving in late January/February. Then swallows are pretty much our next spring migrant, in late February and March.