Flexi Says: A large polar continental air mass forms over central Canada. This high-pressure air mass is typically dry and cold. In winter it joins with the Arctic air mass over Greenland to make an enormous body of cold, heavy air that is associated with freezing weather conditions. In the spring, this air mass shrinks and is replaced along the coast and southern areas by maritime tropical air, which is drawn northward as the middle of the continent heats up.
