Final answer:
The cool temperatures and light rain moving eastward into Washington from the Pacific Ocean are most likely associated with a rain shadow effect. This occurs when moist air masses hit mountain ranges, causing precipitation on the windward side and creating arid conditions on the leeward side.
Step-by-step explanation:
The cool temperatures and light rain moving eastward into Washington from the Pacific Ocean is most likely associated with a rain shadow effect.
As wet air masses move from the Pacific Ocean over the North American continent, they run into the Cascade and Sierra Nevada mountain ranges, which cut off moisture from falling on the leeward side of the mountains. This creates a semi-arid condition in eastern Washington.
The rain shadow effect occurs when prevailing winds carrying moisture rise quickly in elevation up a mountainside, where the air cools and condenses to precipitate out its moisture in the form of rain or snow. By the time the air mass hits the top of the mountain, its moisture is reduced, and the dried air rushes down the other side of the mountain range, resulting in arid conditions.