WeatherTalk: Steam fog after a thunderstorm is explained

Like most fogs, it can disappear just as quickly as it develops.

Steam fog.jpg
Steam fog on a roadway
National Weather Service
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FARGO — If you have ever driven through a thunderstorm, you may have noticed that after the storm has passed, the road appears to be steaming. This steam is actually known as steam fog. There are many ways that fog can form, but steam fog forms through a process known as evaporation and mixing.

After the thunderstorm, the roadways are covered with rain. The sunlight begins to heat the pavement of the roadways. This causes the water to become hotter than the air directly above it, and the water begins to evaporate. This evaporation adds water vapor to the air above it, producing a fog. Like most fogs, it can disappear just as quickly as it develops. Once the water on the roadways evaporates completely, so does the fog. So next time you are out on the roadways (or even at home) and a thunderstorm moves in on a hot summer day, you may be able to spot the steam fog before it disappears.

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