American Meteorological Society Certification (AMS) Practice

The classification of air masses is based on their source regions and properties, which include temperature and moisture content. An air mass described as cold, dry, and stable typically forms over land in polar regions. This aligns perfectly with the characteristics of a Continental Polar air mass, which forms over land (continental) in high latitudes where it is cold and relatively dry.

Continental Polar air masses originate from areas like Canada or northern Eurasia, where they are subject to high pressure systems that foster stability. This stability means that the air mass does not easily rise, leading to clear skies and minimal precipitation when it moves into other regions. Its cold temperature and low moisture content are key attributes that distinguish it from other air masses.

In contrast, Maritime Polar air masses form over the ocean and are moist and potentially unstable. Maritime Tropical air masses come from warm oceanic areas and are characterized by warmth and high moisture content, while Continental Tropical air masses develop over hot land regions and are warm and dry. These distinctions further highlight why Continental Polar is the correct classification for an air mass that is cold, dry, and stable, forming over land.