A/C is less needed in Seattle than in other parts of the US because it cools off substantially at night. I was there two(?) summers ago when some weird inversion layer was both raising the temp (105+ F) and preventing the night time cooling. It was miserable.

Here in the southern US, even when it's only hitting 90 F during the day, the low might be in the upper 70s which isn't low enough to passively cool a house.