The main masses of air, in which we shiver or sweat, are either tropical or polar and either continental or maritime.
In winter, what begins as continental polar air warms and picks up moisture as it spreads over the Pacific Ocean. Continuing with the westerly flow, it arrives at the northwest coast of the United States laden with water, now in the form of maritime polar air with low stratus clouds, fog, and rain.
Similarly, continental polar air spreads south from Canada, and, moving westward, picks up moisture as it crosses the Great Lakes. It deposits the moisture on Buffalo in heavy layers of “lake-effect” snow.
In these mid-latitudes, during the summer in these mid-latitudes, maritime polar air cools the west coasts of the baking continents.