Frontal precipitation occurs when warm air is lifted over cooler air along a frontal boundary between two air masses. It is the dominant precipitation mechanism in mid-latitude regions.
Frontal precipitation is produced at the boundary (front) between two air masses of different temperature and moisture characteristics, where the less dense warm air is forced to rise over the denser cold air. Warm fronts occur when warm air advances and overrides retreating cold air, producing widespread, stratiform precipitation of moderate intensity that may persist for many hours. Cold fronts occur when cold air pushes under and lifts warm air more abruptly, generating a narrower band of more intense precipitation, often accompanied by convective activity and thunderstorms. Occluded fronts, where a cold front overtakes a warm front, produce complex precipitation patterns combining features of both front types. Frontal precipitation is responsible for the majority of annual rainfall in mid-latitude regions and is associated with extratropical cyclones that track along preferred storm tracks. The amount and distribution of frontal precipitation depend on the temperature contrast between air masses, atmospheric moisture content, frontal speed and slope, and orographic effects. Accurate forecasting of frontal precipitation requires numerical weather prediction models that resolve the three-dimensional structure of fronts and their interactions with terrain.