Why do the Coast Mountains receive heavy rainfall and snowfall?

The Coast Mountains, as part of the Pacific mountain system, experience heavy rainfall and snowfall primarily due to their role as an orographic barrier to moist air masses moving inland from the Pacific Ocean.12

When prevailing winds carry moist air from the ocean toward the coast, the mountains force this air to rise along their western, or windward, slopes. As the air ascends, it cools, causing the moisture to condense and fall as precipitation. This process, known as orographic precipitation, is particularly intense during the winter months, resulting in significant accumulations of rain and snow on the western slopes.1342

Conversely, as the air descends on the eastern side of the range, it becomes warmer and drier, creating a rain shadow effect that leads to much lower precipitation levels in those inland areas.134