The Dangers of Freezing Fog

Freezing rain, sleet, and refreezing of melted snow are major winter hazards for drivers, pedestrians, and runners. In other instances, it may look just like another foggy morning on a calm winter day. But beware, if the temperature is at or below freezing, you could be stepping out into a treacherous, glazed landscape. Freezing fog is double trouble: dropping visibility so you can't see the black ice.

What is the difference between fog and freezing fog?

Fog anytime of the year is a driving hazard because it significantly reduces visibility and can be as dangerous as driving in a blizzard with near zero visibility. Freezing fog, however, is even more dangerous because it creates a slippery surface in an environment where it’s difficult to see more than a few hundred feet ahead. The National Weather Service will issue Freezing Fog Advisories when fog develops in a region where surface temperatures will drop below freezing.

How does freezing fog form?

Freezing fog starts out the same way as regular fog. At night, the ground radiates heat into space, especially on a calm, clear night without insulating clouds or the wind mixing the radiated heat back to the surface. However, when the temperature drops below freezing with fog present, the tiny water droplets in the air remain as liquid and become supercooled water droplets. These supercooled droplets can freeze instantly on exposed surfaces creating hazardous conditions for travelers. If there is any good news with the formation of freezing fog, it doesn’t weigh down powerlines or trigger power outages.

How does the National Weather Service handle issuing Freezing Fog Advisories?

Unlike Ice Storm Warnings or Winter Weather Advisories which usually have a short life span, Freezing Fog Advisories usually span at least 8 hours. In a situation where a warm front is overtaking an Arctic air mass, freezing fog can linger for several hours to two days. Typically, this is the case before either the warm air wins out or another weather system comes along to stir up the winds, dissipate the fog and dry out the pavement.

Keep an eye on WeatherBug sources this winter to get the latest winter-related advisories, including Freezing Fog Advisories.

Sources: NOAA, Fox Weather

Image Source: Richard Croft via Wikimedia Commons