The term rain shadow can be introduced at this time. Just as a tree or building blocks the sun, causing a shadow on the opposite side, so the mountains block the rain from reaching eastern Oregon by squeezing it from the air. The Oregon precipitation map can be shown at this time. Point out the wet areas in western Oregon, especially the Coast Range and Cascades, and the generally dry areas in eastern Oregon. Most of the precipitation in Oregon falls west of the Cascades.
Terrain plays a very significant role in precipitation distribution.