I don't remember my timings all that well except that we were running Fall Chinook updates and fisheries in late July/eraly August. But this was PS and the glaciers may have encouraged movement.

I know you're more familiar with the Chehalis but what don't you think it is Summers? One of my rules of fish biology is that what you don't kill actually spawns. So, a Summer that arrives and gets its tail upstream before the nets goes in is more likely to spawn.

I think that not killing mantra is what has helped some PS streams to have January spawning, and returning, coho.