black frost

1. A dry freeze with respect to its effects upon vegetation, that is, the internal freezing of vegetation unaccompanied by the protective formation of hoarfrost.

A black frost is always a killing frost, and its name derives from the resulting blackened appearance of affected vegetation.

1. Among some fishermen, a steam fog that extends above the bridge level of the fishing boats.
   If the steam fog does not reach this height, it is a white frost.