(WKBN) – A common scene in the morning during summer months is early morning fog, and that has been no different this year in the Valley.

Have you ever been driving down a road in the early morning hours and noticed that fog develops almost at random? Did you know that there are different types of fog? Today, you are going to learn more facts about fog than you knew existed. Are you ready to be a fog expert? Let’s go.

Fog is just a fancy word for clouds at ground level

The first factoid is that fog is just clouds at the ground. Clouds are composed of small water droplets or ice crystals and are formed when water vapor is transported vertically and cooled. The cooling of the water vapor results in condensation, which is the transition of a gas (water vapor) to a liquid (cloud droplets). Condensation occurs when the air temperature and dewpoint temperature (the temperature at which condensation forms) are the same value. You might understand that there is vertical motion in the atmosphere since you can actually see the definition of the clouds, but how does this occur at the ground?

A foggy road with low visibility.
A foggy road with low visibility.

Heat release from the surface

Another fact that you might be interested in learning is that the heating of the surface from the sun is what causes the air temperature to increase. The sun first heats the ground which then heats the surface through a process called conduction. However, when the sun sets the cooling process is the opposite. The surface of the Earth cools first by releasing heat that was absorbed during the day. In fact, this is the first and main way that fog develops over an area.

Graphic explaining how the surface of the Earth cools during the night.

What are the different types of fog?

Radiation fog

The first and most common type of fog in our area is radiation fog. This occurs when heat and water vapor are released from the surface of the Earth and eventually cools to condensation. This is what occurred across much of the Valley Monday.

Fog at the Youngstown-Warren Regional Airport today (August 22nd, 2022).

Upslope Fog

Another type of fog is called upslope fog. This occurs in mountainous regions where air is forced to travel up a mountain. When the air moves upwards, it cools and the water vapor will condense into clouds at the top of the mountain. This is very common ahead of snow storms in the Rocky Mountains.

Snow and upslope fog in Fort Collins, Colorado taken by Adam Clayton on February 7, 2020.

Precipitation Fog

Another form of fog occurs right after precipitation on a hot summer day. You can sometimes see this on roadways after a heavy thunderstorm during the day in the summer. This phenomenon occurs most commonly after large hail storms which act to cool the surface of the Earth and produce fog.

Fog after a hail storm in Earlville, IL from the National Weather Service (NWS).

Advection Fog

The last type of fog is responsible for the scenes in one of the most famous cities on Earth: San Francisco. The ocean water near San Francisco is often cold relative to the surrounding air. When the air passes over the cold water, it is cooled to saturation and fog forms across the area. This can also occur during the winter months due to a snowpack.