Freezing rain is a treacherous winter weather phenomenon that can quickly transform roads and sidewalks into extremely hazardous surfaces. This occurs when a layer of warm air exists above a layer of freezing air near the ground. As raindrops fall through the warm air, they melt, and then as they pass through the freezing air, they become supercooled but remain liquid. Upon contact with any surface that is at or below freezing—such as roads, sidewalks, trees, and power lines—the supercooled raindrops instantly freeze, forming a glaze of ice.