When an air mass moves slowly over a large area that has fairly uniform properties of temperature and moisture the air-mass acquires the temperature and moisture properties of the area it covers.
Charactiristics of an unstable air-mass include:
Cumuliform clouds.
Showery precipitation
Rough air
Turbulence
Good visibility
Characteristics of a stable air mass include:
Startiform clouds
Fog
Continious precipitation
Smooth air
Fair to poor visibility
When the air mass move out of their regions they come in contact with other air masses of different properties.
The zone between two different air masses is a frontal zone or front.
Across this zone temperature humidity and wind often change rapidly over short distances.
The three principal types of fronts are
Cold front
The warm front
Stationary front.
Frontal waves and cyclones usually form on slow moving cold fronts or stationary fronts.
