Cold
The boundary between a cold and warm air mass is called a front. One type of air will replace another as a front passes.
it is called a cold front
it is called a cold front
An occluded front.
a warm front
it is called a cold front
it is called a cold front
it is called a cold front
it is called a cold front
it is called a cold front
it is called a cold front
it is called a cold front