What Is Freezing Fog?
Freezing fog is fog which contains supercooled water which freezes upon contact with objects it encounters, forming a layer of thin ice or rime. It differs from ice fog, which is made up of tiny particles of ice. Many regions of the world can experience freezing fog, especially during the winter months, when the air temperature can drop below freezing, creating the conditions necessary to create supercooled water droplets.
For ice to form, it needs something to crystallize around. In the case of freezing fog, the water droplets in the fog are below the freezing point, but they have nothing to form on, so they remain in a liquid state. As soon as they come into contact with buildings, trees, and other objects, they freeze. This can create hazardous conditions because the ice forms a thin slick, and the freezing fog can also damage plants and trees by causing them to ice over.
Sometimes, freezing drizzle follows freezing fog. Freezing drizzle has larger droplets of supercooled water which freeze on contact. Since the air temperature is usually below freezing, the ice deposits which form can remain. Freezing fog and drizzle can create problems with objects which freeze over and become nonfunctional because of the cold and ice. It is also usually unpleasant to be outdoors in these weather conditions because of the cold and the formation of ice crusts on garments.
In the case of ice fog, the temperature needs to be extremely low. Ice fog is usually seen in polar regions, where temperatures and weather conditions are such that clouds composed of ice crystals can form. Forecasts for ice fog outside the polar regions do happen, but they are quite rare, as the conditions needed for it to occur are not very common. There may be other weather warnings in place when ice fog is in the forecast, as the extreme cold can make it dangerous for people to be outdoors for extended periods of time.
When a weather forecast warns that freezing fog may occur, there are some precautions which people can take in advance. Vulnerable plants should be covered to protect them from frost, and it is advisable to curtail driving activities because the rime which forms as a result of freezing fog can make it dangerous to drive. Exposed pipes should also be covered if they are not already insulated to protect them from harsh winter weather.
Written by S.E. Smith
