Monsoons are continental weather events produced when intense summer sunlight heats land more than ocean. But new supercomputer simulations show that North America's only monsoon works differently. The North American monsoon, which drenches western Mexico and the American Southwest each summer, is generated when the jet stream collides with the Sierra Madre mountains, which diverts it southward and upward, condensing moisture laden air from the eastern Pacific into torrential rains.

Source: Summer rains in American Southwest are not your typical monsoon