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Clearing the air over the different types of fog

Hills with fog.
Ricardo Gomez Angel
Fog is basically a cloud a ground level.

Every week WAVE 3 meteorologist Tawana Andrew breaks down what we know and what we don't about the climate and weather here in Louisville.

Bill Burton: It's time for us to take a look at the Science Behind the Forecast as I am joined by WAVE 3 meteorologist Tawana Andrew. Good morning, Tawana.

Tawana Andrew: Good morning. Today's topic can be a little spooky if you think of it that way.

BB: It can be because fog is always a part of those kinds of spooky movies. So that's our topic today. Well, fog, not spooky movies. What do we need to know about fog?

TA: Yeah, well, we know about fog, especially as we deal with rain and clear skies and things like that, on pretty muggy mornings. And the National Weather Service defines fog as water droplets suspended in the air at the Earth's surface, or if you want to think of it another way. Fog is basically a cloud with its base at ground level. So as you're walking through fog, you're walking through a cloud, which I think it's pretty cool. And there are a couple of types of fog. And for our region, we see a few we see advection fog. That is when you have warm moist air moving over a colder surface that could be ground or water. And this cools the air near the surface below its dew point that can cause some fog, another type of fog that we see, radiation fog. So this is the one that we usually see, when we have skies that are clear the wind is light. And this allows the heat from the surface to be efficiently released into the atmosphere. And that will actually help to drop temperatures due towards the dewpoint. If we've had precipitation recently, then the fog formation will be accelerated. That is why after we deal with some rain, the skies clear out. We have these crazy foggy mornings that is radiation fog. One that we typically don't see often but will happen in the fall or early winter will be steam fog. And this is one of my favorites if you can have a favorite type of fog. Sure, why not? Why not right? Steam fog is amazing because you have colder air moving in over warm water. And it adds water vapor to the air condensing it into fog. So think of steam coming off of your coffee or tea, looks exactly like that water. And then there's another type of fog, frontal fog. So when you have let's say a cold or a warm front, moving into or through an area, they can actually cause fog to form. So with pre and post frontal fog, you have rain falling into stable cold air, this actually raises the dew point for the other types of fog. You see the dew point is dropping. But for this one, you see the dewpoints being raised and that is what causes the fog of formation. Something that I always hear a lot of people say, even meteorologists will say this is that the fog burns off. Technically, it's not burning off. Once inside it comes up as the sun rises, what you'll have is that the air and the ground are going to be warming up because you know the sun is beaming down on it now. And that will cause the air temperature to rise above the dew point. So as the air temperature and dew points separate, the fog droplets are actually evaporating. They're not burning off. They're evaporating. So if you want to now spread a new fact around the water cooler. There it is.

Bill Burton is the Morning Edition host for LPM. Email Bill at bburton@lpm.org.

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