I'm gonna take a wild guess and say there is alot of humidity in Washington with all the rain you get (how can you live there?) Even when it's not cold or raining the humidity can be enough to do this. When you stop you're constantly shaving off a tiny, microscopic layer of rotor surface, revealing bare metal. Bare metal+moisture=squeeky brakes. Once you stop a couple times, this layer of corrosion is cleaned off. It's an ongoing process here in Cleveland too. Certain wheel cleaners, road salt, and other things can do this too. I wouldn't worry 
