Prevailing westerly is a wind that blows over the North and South middle latitudes from west to east. In the Southern Hemisphere, prevailing westerlies over the ocean blow with such force that sailors call this region the “roaring forties.” The winds are not steady because they are often interrupted by cyclonic storms. Over the land masses of the Northern Hemisphere, the westerlies are often turned from their course by mountain ranges. The United States and the southern half of Canada lie within the path of the westerlies.
