Why is there more rain in western Washington than in eastern Washington?

Western Washington experiences more rain than Eastern Washington due to the presence of the Cascade Range, which creates a rain shadow effect. As moist air from the Pacific Ocean moves eastward, it rises over the mountains, cooling and condensing to form precipitation on the western slopes. Once the air descends on the eastern side, it warms and dries out, resulting in significantly less rainfall in that region. This geographical feature leads to a stark contrast in climate between the two sides of the state.