You may have heard of freezing rain, but have you ever heard of freezing fog? This weather phenomenon can quickly turn a winter wonderland into a travel nightmare. The tiny droplets in fog freeze onto exposed surfaces once the temperature drops below freezing.

The National Weather Service said the fog could lead to black ice and limited visibility, and urged drivers to exercise caution.

If The freezing fog sticks around for while, we will see the ice begin to build up on surfaces such as tree branches, grass, stairs, sidewalks, roads, bridges and powerlines. Freezing fog can also cause black ice to form which can cause slippery conditions for walking, driving on roads especially on the bridges.

Warmer temperatures are forecast for the Chicago area early in the week, but freezing rain Tuesday could leave roads slippery Wednesday. By Friday, high temps will hit the 20s, and Friday night the wind chill could drop to minus-20.

Freezing rain is "supercooled," say meteorologists, and will instantly refreeze when it touches anything on the ground that's at or below 32 degrees. Freezing rain can lead to a glaze of ice on roads and sidewalks.

NWS meteorologist Matthew Day told Newsweek that freezing fog is an "unusual" occurrence for the Norman, Oklahoma, NWS office, which issues forecasts for north Texas as well. Although dense fog is normal for the region this time of year, temperatures aren't always cold enough to cause the fog to freeze.

Forecasters say freezing fog is possible for southeastern Virginia Sunday, and odds are increasing for a light accumulation of snow Monday.

Frozen pipes are a nightmare to deal with when the temperature drops, but it can be prevented. Frozen pipes can happen at any temperatures below freezing, depending largely on how insulated the pipes are, so it's always best to be cautious. Here are some tips from Providence Water on the best way to avoid it.

On Sunday at 8:32 a.m. the NWS Raleigh NC issued an updated freezing fog advisory in effect until 10 a.m. The advisory is for Person, Granville, Vance, Warren, Forsyth, Guilford, Alamance, Orange and Durham counties.