What is Freezing Fog?

As temperatures drop around the country, fog can become much more dangerous this time of year.

Fog can form in a variety of weather conditions. When warm raindrops evaporate near the ground into a layer of cool, dry air, for example, humidity can reach 100% and create what’s known as evaporation fog.

In winter, though, those water droplets in the air can stay liquid until they contact a surface with below-freezing conditions. This condition, known as freezing fog, can instantly create a dangerous layer of ice.

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Everything from stairs and handrails to tree branches and roadways can be susceptible to freezing fog when the conditions are right.

Airplanes are a particularly dangerous example. When freezing fog hits a plane’s fuselage, a layer of ice can form that prevents the wings from generating the life that makes flight possible.

That’s why airports around the country have de-icing equipment to treat planes flying in hazardous winter conditions.

Unfortunately, freezing fog has a history of creating disastrous situations.

In our ranking of the “10 of the worst ice storms in U.S. history,” Idaho’s famous New Year’s Day ice storm in 1961 set a record with 8 inches of ice accumulation in the state’s north-central region.

Because black ice can be particularly difficult to see, experts warn that drivers should exercise extreme caution when traveling in conditions where freezing fog is possible.