Frontal lifting
Where a warm air-mass and a cold air-mass are in contact, their line of separation, at sea level, is called a front. The boundary between them is not vertical. It is inclined towards the colder air-mass because the cold air, being denser, acts like a wedge and lifts up the warm air.
In the case of a warm front, the slope is gradual and the upsliding warm air forms stratiform clouds – nimbostratus, altostratus, cirrostratus and finally cirrus. In the case of cold front the slope is very steep and the upsliding warm air forms cumulonimbus and cumulus clouds.
