In the Pacific Northwest, why is eastern Washington extremely dry compared to western Washington?

The phenomenon of eastern Washington being extremely dry compared to western Washington is primarily due to its location in relation to the Cascade Mountain range, which creates a rainshadow effect. As moist air from the Pacific Ocean moves eastward, it encounters the Cascades. The mountains force the air to rise, cool, and condense, resulting in precipitation on the western slopes. By the time this air descends on the eastern side, it is significantly drier, leading to the arid conditions found in eastern Washington. This explains why the correct answer is based on the rainshadow effect created by the Cascade range, a crucial geographical factor in determining the climate of the region.

In contrast, the other options do not effectively account for the unique climatic conditions in eastern Washington. For example, elevation does influence weather patterns, but the elevation alone does not explain the significant difference in rainfall between the two regions; it is the rainshadow effect that plays a dominant role. Human activity may impact local climates, but it is not the primary factor for the widespread dryness observed in eastern Washington. Additionally, while eastern Washington does exhibit features of a continental climate, this classification alone does not sufficiently address the primary reason for the stark contrast in moisture levels when compared to western Washington.