What defines an airmass?

An airmass is fundamentally defined as a large body of air that has relatively uniform characteristics in terms of temperature and humidity throughout its horizontal extent. These properties are largely influenced by the surface over which the airmass originates, which can be land, water, or even ice, giving rise to specific types of airmasses such as maritime tropical or continental arctic.

The uniformity means that within this mass of air, the weather conditions can be fairly consistent until it moves and interacts with different air masses or geographical features. This uniformity is why the definition centers on a body of air possessing substantially the same properties. Understanding this characteristic is crucial for forecasting weather changes, as airmasses play a significant role in determining local weather patterns and conditions.