Three times a week, I walk across campus to class. After 8 weeks of the quarter, I have worn a jacket exactly once, because it is generally dry and warm enough to do without a jacket.
To be completely fair, I missed a few days due to travel and I don't know how the weather was then. And, on some of days it rained at other times, such as overnight, which keeps the region green but doesn't mar our enjoyment of it. Finally, at least once it was misting outside, but not enough to justify a jacket. Some days it was overcast, on others gloriously sunny.
Seattle has an undeserved reputation for non-stop precipitation. A popular joke says "It only rains once a year in Seattle, but it lasts 9 months." In reality, Seattle doesn't get very much rain.