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Freezing rain occurs when the temputer ins below freezing
When it gets above freezing when it rains then it gets below freezing it causes freezing rain.
Freezing rain
Sleet
There has always been freezing rain.
Freezing rain is composed of super-cooled waterwhich freezes on contact with any freezing surface, forming glaze ice.
Ordinary rain has a temperature above freezing and will not instantly turn to ice.