Cyclonic rain occurs due to the convergence of extensive air masses. When two contrasting air masses like cold polar air mass and warm westerly air mass coming from opposite directions converge along a line a front is formed. The warm wind is lifted upward along this front where the cold air being heavier settles down.
Such cyclonic fronts are created in temperate regions where cold polar winds and warm westerlies converge. The warm air lying over cold air is cooled and gets saturated and condensation begins around hygroscopic nuclei.
The lifting of warm air along the cyclonic front is not vertical like convective currents rather it is along an inclined plane. The front is a zone of intensification of low pressure, cooling condensation, cloud formation, and rainfall- the entire process is known as frontogenesis.
Frontal rainfall is most common in mid-latitudes as it is a zone of convergence of warm westerlies and cold polar easterlies. Frontogenesis is also the basis of the formation of temperate cyclones. Temperate cyclones also produce frontal rainfall in India during the winter season in North-Western parts of India which are known as western disturbances.