The air at the equator is hot and the air at the poles is cold, when warm air rises cold air rushes in to fill the empty space. We call this wind. In Ontario our prevailing winds come from the west. Air Masses Large body of air, Warm masses from the equator, Cold masses from the poles, Air masses that come from over water tend to be warmer and wetter. When cold and warm air masses meet, the warm air is forced up the air rushes in to fill the space, the warm cool, condense, and precipitate.
