Some parts of the region got snow yesterday due to the convergence zone*. Precipitation causes evaporation that cools the air. This only lasts minutes, but then melting snow robs the air of energy which causes even more cooling. Yesterday, that was enough to drop the snow level down to the surface in some places.
* NW wind becomes split by the Olympics, then "converges" over the Sound, creating updrafts. Those updrafts cause convection and then precipitation.