Clear ice forms when the drops are large. Upon impact, the liquid portion of the drop flows over the aircraft surfaces, gradually forming a smooth sheet of solid ice. Clear ice will normally form while flying through cummuliform clouds and through freezing rain. Rime ice forms while flying through stratified clouds and freezing drizzle. When the drops are small, the drop freezes prior to spreading.
Air is trapped between the small frozen drops, giving the ice a white frostlike appearance.
The term visible moisture may lead to a wrong conclusion about the imminence of structural icing. Clouds are the most common form of visible moisture. Rain, drizzle, and mist are often transparent to the naked eye and should also be Meteorological Conditions exist, icing may occur when flying through freezing rain or freezing drizzle. Freezing rain and drizzle may be found in frontal zones. When rain is formed aloft and drops through air at a temperature below freezing, it becomes supercooled, and source for structural icing.