Refer to figure.
Freezing rain, or rain ice, is a very dangerous phenomenon which occurs most often underneath a warm front (within the cold sector), where relatively warm rain is falling from the warm air above, and hitting the airframe below (which is below freezing temperature). This rain then can instantly freeze onto the airframe, causing a fast build up of ice onto the aircraft surfaces. The annex above shows the location of the rain ice triangle, which is the region of danger for this phenomenon.
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