Air mass
Models & data meteorological air mass
An air mass is a large body of air with broadly similar temperature and moisture. Its origin explains much about the weather, while its journey changes it further.
Air takes on its surroundings
Air remaining over a large, fairly uniform surface gradually takes on its characteristics. A warm ocean affects it differently from a cold continent. The resulting air mass may cover much of a country or an even larger region.
The names tell us where it came from
- Maritime: influenced by the sea, often moist.
- Continental: influenced by large land areas, often drier.
- Polar or Arctic: from cool or very cold source regions.
- Tropical: from warm source regions.
The labels can be combined: maritime polar air, for example, starts as cool air influenced by the sea.
Air changes on its journey
Cold air can gain heat and moisture over warm water. Warm air cools over cold ground. Season matters too: continental air may be very cold in winter and hot in summer. Its origin is a clue, not a complete weather report.
Where different air masses meet
A front may form between contrasting air masses. Lifting there can produce clouds and precipitation. Conditions are still not identical throughout one air mass: terrain and time of day continue to have an effect.