The document discusses different air masses that affect weather in North America. It describes how a maritime tropical air mass from the Pacific Ocean brings summer monsoon storms to the Sonora Desert region. It also explains that cold, dry air masses from the Canadian tundra region bring frigid winter conditions to parts of the United States. Additionally, it notes how air masses develop the temperature and moisture properties of their source regions and how these air masses can later modify local weather patterns as they move across landscapes.
