Western Washington is a region of the United States defined as that part of Washington west of the Cascade Mountains.
It is known as being far wetter in climate than the eastern portion of the state, which is due in main to the effects of the Cascades rain shadow. The estimated population as of July 1, 2004 was 4,831,986 out of Washington's estimated population of 6,203,788. This makes the population comparable to that of Colorado at an estimated 4,601,821.
US Census Bureau for Washington