Freezing rain forms as snow, melts as it passes through a warmer layer of air and then becomes a super-cooled liquid, which freezes on impact. Freezing rain normally forms on the leading edge of a warm front overtaking a mass of cold air, forming the alternating layers of warm and cold air, according to Reference.com.
Freezing rain leaves an icy glaze on everything it touches. This glaze grows thicker with each super-cooled drop that strikes the surface. The weight of the ice causes a large number of problems. Ice over 0.2 inch thick breaks tree limbs already under stress due the tree's dormant state in cold weather. If the heavy limbs fall on power lines, they cause power outages. The ice also places stress on power lines, poles and insulators. Ice forms on roadways eliminating traction for vehicles and making travel difficult and dangerous. Unlike snow or sleet, freezing rain forms a continuous sheet of ice that wind is unable to move, leaving warmer temperatures to melt the ice as the only way to improve road conditions. Freezing rain is dangerous for aircraft of all sizes as it adds weight to the plane and changes the shape of the airfoils, reducing lift and increasing drag. According to Reference.com, crash investigators believe freezing rain was responsible for the crash of American Airlines Flight 4184 in 1994, which took the lives of 68 people.