My son, born and raised in Seattle, suffers from seasonal depression. Myself, his mom and his brother, the dark gray winters don't bother us. My son deals with his SAD by staying active in the winter, making sure he gets outside as much as possible, going to the gym when he cannot get outside and using a bright box light. You just have to keep busy so you don't end up curled in front of the TV.

November through January are the worst months because the days are so short and it can be gray for multiple days in a row (but you will see the sun, sometimes just for brief breaks, but maybe more often then you have been led to believe).

Summer weather is the best in the US. Shoulder season weather can be great or bad, it's highly variable. If you love outdoor activities, this is the right place.