The Minnesota Department of Transportation warns motorists that current and forecasted temperatures create conditions for black ice, an invisible hazard that catches drivers off-guard and causes crashes. Black ice creates the appearance of a wet surface, but it is actually a thin, clear layer of ice on roads and bridges.
Black ice forms when melting snow refreezes or when rain, drizzle, mist or fog freezes. It is most common at night and very early morning when it is dark and temperatures are lowest. Black ice and refreezing often occur on overpasses and bridges and near lakes and rivers, and in shaded areas. The hazards can also form when snow temporarily melts from auto exhaust emissions or tire heat as well as from moisture vapors given off by industries located close to the highway.