Cold air mass moves to replace a warm air mass giving rise to a cold front. The different air masses do not mix as they have different temperatures and densities.
This is because the warm air has less density than cold air. Clouds are the best example as the moisture in the air condenses as the warm air rises and cools.
These are the masses of cool and condensed air. If we pass through a cold front, we definitely feel the cool air and dryness.
