The cascade mountains run north and south through the middle of both washington and oregon. the west side of these mountains (seaward facing) receives an abundance of rain while the east side (inland facing) is remarkably dry. this sharp climate change from one side to the other is largely the result of:

Cascade mountain is mountain located in Bow river valley. extends from southern british columbia to washington the western side of the mountain is windy and eastern side is dry due to it acts as a barrier to the force of winds.

Explanation:

Being a major mountain range of North America it is non volcanic. Also called as Canadian cascades. The highest peak is to mount rainier 14,000 feet. This range runs from north to south thus blocking the winds from directly entering into the interior of the continent and creating a rain shadow effect on the other side of the landmass. The western side of the mountain thus gets an abundance of rainfall and receives the turbulent winds blowing away from the coastlines.  Which is dry on the other side of the mountain and hence the mountain comes under a rain shadow effect.  This sharp climate change is in respect of the mountain ranges creating a barrier type of environment, hence known as an Orogenic climate change or shift.