Cyclonic rainfall, also known as frontal rain, is caused when two air masses of different temperatures meet. Warm air and cool air don´t mix, as they have different densities. As the warm air rises over the heavier cool air, it cools and creates a front; clouds form and produce rain.
A warm front occurs when a warm air mass moves into a cold air mass As they collide, the warm air quickly rises over the cold air, losing heat in the process. The resulting storms are characterized by a prolonged period of heavy rainfall. As the front begins to pass, the rain becomes lighter and eventually tappers off. After the warm front passes, the temperature becomes warmer, but the sky is normally cloudy.
A cold front occurs when cold air meets warm air and wedges itself underneath the warmer, lighter air mass. As the cold air moves quickly to the Earth´s surface and as the warm air is forced upwards, large clouds are formed. Characteristics of a storm created by a cold front include a rapid drop in temperature and heavy rainfall, alongside thunder and lightening. Once the front passes, the weather will improve and the winds will change direction.