Fog is a common meteorological phenomenon that occurs when the air temperature and the temperature at which the air would become saturated, or the dewpoint, meet at the same temperature point. Once this occurs, tiny water droplets come together to create a cloud-like structure near the ground, otherwise known as fog. This becomes dangerous during travel because it acts to reduce visibility and becomes worse the more dense it is.
There are many different types of fog, in terms of what conditions the fog forms under, and certain types can be more prone to various regions of the country at different times in the year. Here in Kansas, we are no strangers to fog. Not only can fog cause issues in the spring and fall, but the winter season can also bring about more fog events if there is enough moisture on hand and a lack of cloud cover to keep temperatures warmer overnight.
After the New Year’s Day 2021 snowfall event, portions of eastern and southcentral Kansas dealt with the effects of fog as sunshine returned the days following New Year’s Day and the snow began to melt. This set up not only a perfect scenario for fog to form, but for temperatures to drop below freezing and for freezing fog to become a concern. The snow would melt during the daytime, and it would leave the layer of air just above the ground full of moisture as the liquid water slowly evaporated into the air above it. Overnight, temperatures would fall with a clear sky in place and the air over the snowpack would become saturated. This would lead to the development of fog that would become dense in spots.
Not only would this fog cause a reduction in visibility, but temperatures with the snow in place were below freezing as the fog formed leading to a freezing fog setup. In this setup, the tiny suspended water droplets in the air would be supercooled, which means they can more easily freeze on contact with a surface that has a temperature at or below 32°F. When the fog is dense, more water particles are able to collect on surfaces such as roadways, bridges, sidewalks, handrails and vehicles leading to ice accumulation. This not only creates issues with travel because the visibility has been reduced, but on top of that, drivers have to be mindful that areas of black ice may have formed that they may not be able to see due to the reduced visibility.
As we continue into the colder winter months, pay special attention to temperatures on mornings where fog, especially dense fog, is present as slick spots on bridges and overpasses will be quick to form.