Which air masses are the most common to form over North America in winter?

The most common air masses to form over North America in winter include continental Arctic (cA), maritime Arctic (mA), and maritime Polar (mP).

Continental Arctic air masses are characterized by their cold and dry conditions, forming over the icy regions of the Arctic. These air masses are crucial during winter as they bring frigid temperatures to large parts of Canada and the northern United States.

Maritime Arctic air masses originate over the cold waters of the Arctic Ocean. They are less cold than cA masses but still significantly influence winter weather, bringing cool temperatures and moisture, often leading to overcast skies and light precipitation.

Maritime Polar air masses develop over the northern oceans and are usually characterized by cool, moist conditions. In winter, they can bring precipitation and cloud cover as they move southeastward into the continental United States, contributing to winter weather events.

This combination of air masses plays a significant role in shaping the winter climate across North America, leading to cold temperatures, snow, and variable weather patterns. Other air masses, like tropical or continental tropical, are less prevalent during the winter months in this region, making the combination of cA, mA, and mP the most representative for that season.