There are different types of fog. They are categorized by the method by which they are formed. Essentially the result is all the same. Fog is simply a low-lying cloud of water droplets that are suspended above the ground.
Evaporation fog forms when cold air passes over water or land that is warmer than the air above it. Upslope fog is created when winds blow air up a mountain. The air cools and forms water droplets. This particular form of fog has the potential to be long-lasting. Radiation fog is formed as the ground cools after sunset. It is most common on summer or fall nights with clear skies. Advection fog happens as moist air passes over a cool surface and is then cooled. All of these different forms of creating fog can turn into frozen fog in the right conditions.
Simply put, freezing fog is when the water droplets freeze upon contact with a hard surface. Frozen fog requires temperatures below freezing and it happens most often in the Antarctic and Arctic. A thin layer of ice forms over a surface. It is called rime ice.
Rime ice is a unique form of ice that only happens with freezing fog. It is often very feathery, and you can tell which way the wind was blowing as it is “caught” and frozen in a specific direction. Rime ice is not clear, but very white. It does not cause a lot of damage to the object it is attached to, but it can be hard and slow to get rid of. Shards of rime ice can extend out past the object. It is all created by freezing fog.
While freezing fogs leave behind some beautiful scenes, they can create very dangerous situations. When you are driving, the fog can actually freeze some of the mechanisms in the vehicle and cause them to malfunction. The roadways can become covered with ice, and that always brings difficulty. It becomes even more of an issue where there are bridges. Being surrounded by the freezing fog means that both the underneath and top of the bridge is covered in ice and will remain slick for a very long time.
Rime ice is very beautiful. Once the fog clears the trees have a striking white appearance that is almost magical. For some locations freezing fog is the sign that old man winter has come and kissed the area with his winter blessing.
