What type of precipitation is formed by a warm layer aloft over a freezing surface?

The correct type of precipitation formed by a warm layer of air above a freezing surface is freezing rain. In this scenario, when snow forms in the warm layer, it melts into liquid droplets as it falls. If these droplets then pass through a colder layer of air just above the freezing surface, they remain liquid. When they make contact with the surface, which is below freezing, they instantly freeze upon impact, resulting in a layer of ice.

This unique process is what distinguishes freezing rain from other forms of precipitation such as sleet or snow. Sleet, for instance, occurs when ice pellets form; they typically do not become liquid before reaching the ground. Meanwhile, snow does not involve the melting phase at all and falls as frozen crystals. Hail, on the other hand, forms in strong thunderstorms under different conditions, involving repeated updrafts and a significant amount of water in a colder layer, which is not the case here. Thus, freezing rain effectively captures the specific conditions described in the question.