Frontal rainfall is a type of condensation that occurs when a cold front meets a warm front. Warm air is less dense than cold air. When the two air masses meet, warm air is forced over the cold air, because it is less dense. When the air becomes fully saturated, rain begins to fall.
In addition to frontal rainfall, other types of weather condensation include convection and relief rainfall. Convection rainfall is common in warmer areas of the planet, including zones around the equator. Relief rainfall is caused by moisture from large bodies of water begin carried inland by prevailing winds.