Clear Ice refers to a solid precipitation that forms when air temperature is between 32 degrees and 27 degrees Fahrenheit and there is a presence of super-cooled, large drops of water (from freezing fog). A rapid build up and slow dispersing of latent heat of fusion favors conditions for the formation of the transparent ice. A similar phenomenon occurs when freezing rain or drizzle hit’s a surface and freezes causing what is known as glaze.
When clear ice forms on the ground, it is commonly called Black Ice, and can be extremely hazardous. Clear ice is more dense and more homogeneous than hard rime, a white ice which forms when droplets from fog freeze to objects’ surfaces. Like rime, however, clear ice builds up on branches and overhead lines, where it is particularly dangerous due to its high density.