I'm not sure of this ID: the bands seem too white, and the pattern doesn't look quite right. It's also slightly out of range, according to the map in Kaufman's butterfly book.
This showy B&W moth was in a park between a developed area and wetlands next to a lake. It was flitting amid the vegetation, conveniently pausing to rest on grass and then an elderberry bush. I've seen this same species in 2013 & 2014 about 10 miles from where I saw it yesterday. It seems to be common in the Homer, Alaska, area.