What is the source region of a cold and dry (cP) air mass?

A cold and dry (cP) air mass is typically formed over land areas where the temperature is low and the humidity is also low. The source region for this type of air mass is generally characterized by cold, dry conditions that facilitate the development of such air masses.

Central Canada fits this description well. It has large land areas that experience cold temperatures, especially in the winter, and low humidity levels, making it an ideal source region for continental polar air masses. These air masses can then move southward, bringing cold, dry air into lower latitudes.

In contrast, the other regions mentioned do not provide the conditions necessary for the formation of cold and dry air masses. The Gulf of Mexico, for instance, is known for warm and humid air, while the Atlantic Ocean typically produces milder, moist air. The Rocky Mountains can produce various air masses but are more associated with influences from maritime air due to their proximity to oceanic sources. Therefore, Central Canada is the correct source region for a cold and dry (cP) air mass.