Why is the pacific northwest receives so much precipitation?

The Cascades rain shadow can be described as such: ocean-influenced moist air masses are forced to rise when they meet the tall moun- tains. The rising air cools, condenses, and the moisture falls as precipitation. On the leeward (dry) side of the mountain, the now dry air warms and sinks.

The high amount of humidity explains the impressive amount of rain that falls on the Pacific.

Explanation:

In the Pacific Northwest there is a wind current that travels from west to east. It enters the continent and hits a mountain range in a process called "orographic ascent". The jet ascends, the humidity condenses, and the winds coming from the east meet in the opposite direction with this current and push the clouds. That is why the rains are so strong on the Pacific coast. The high amount of humidity explains the impressive amount of rain that falls on the Pacific. When this moist wind blows inland, the moist air may rise into the atmosphere enhancing the clouds and strady rainfall.

Water evaporates from the ocean and is carried over the Northwest , where it cools and condense into the rain.

There is also a low-pressure systems at the surface which is the driving force that produce rain and winds and this allows large storms to crash into the coast with ease. Some of these storms can be enormous and can cause significant wind damage and flooding.