LOUISVILLE, Ky. — Living along the Ohio River there are often times in the morning where a thick blanket of fog covers the river and spills over onto land. Other times it’s only patchy. How is this happening?
A common way is through a process called advection. In order for advection fog to form, the temperature of the water needs to be a good deal colder than the air temperature.
Then, you need warm, moist air to pass over that cold water — this is the advection. The cold water cools the warm air above it to saturation, and fog is made. Of course, this does not just happen over rivers. Lakes, ponds, and land can all experience advection fog.
Over the Ohio River, the fog will only last for several hours, but on the west coast, where this process is most common, it can last for several days.
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