6 Storm Team Weather School: How fog forms

6 Storm Team Weather School

KNOXVILLE, Tenn. (WATE) — If you’ve lived here in East Tennessee for some time, you know that we often see fog.

In fact, our area sees some of the most days per year with fog. Areas from Knoxville to the Tri-Cities see more than 40 days per year and from Knoxville to the Plateau, about 30 to 40 days per year there is fog.

We see a couple of different kinds of fog here in East Tennessee. One of those is steam fog. This is because we have so many lakes, rivers, and streams across the area. We usually this in the fall or heading into the winter as cold air moves over warm waters of the more shallow areas and usually what happens is you start to see water evaporate and move up into the sky. Air just above the surface of the water starts to get heated up and it interacts with that colder air as it rises up forming steam. It’s kind of like you were boiling water on a stove, rising that warmer air into cooler air and you get steam or steam fog.

Another type of fog we often see in East Tennessee is Radiation Fog. What happens as we go into the night, the daytime heat, the sun heating up the Earth’s surface, go back up into the sky with lighter winds. Meaning a thin layer of moisture develops under this drier air and as the air rises once again, it goes through that moist layer, it cools, it condenses, and we see is that fog develops. So, as it rises, it turns into a vapor or into fog.

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