Breaking down types of fog, how they form

AccuWeather

AccuWeather's Anna Azallion explains what fog is and the different types of fog.

Transcript

00:00A very foggy start to the morning for many.

00:03This is a look at New York City.

00:05The Empire State Building, you can barely

00:07see it because of the fog, especially

00:10as you go a little bit higher in the building.

00:12I know they're not the only ones starting off

00:14their morning with some fog.

00:15I saw some on my drive into work here at AccuWeather HQ

00:18in State College, Pennsylvania.

00:20A lot of us dealing with this this morning.

00:22But have you thought about exactly what fog is?

00:25Well, it's basically a low cloud.

00:27It forms when conditions are right

00:29and when the temperature reaches the dew point.

00:31But there are different types of fog.

00:33So let's break down how a few different types form.

00:36First, we'll start with a lot of the fog

00:38that we're seeing this morning, radiational fog.

00:40Now, you need calm winds for this fog.

00:42And a key element here, think about it.

00:45During the day, the sun heats the ground.

00:47Then at night, that heat rises.

00:50The ground cools.

00:51Next, another key element, this thin layer of moisture.

00:55That's underneath drier air and above the ground.

00:57And rising surface air,

01:00it passes through this layer of moisture.

01:03Then it doesn't absorb much heat though.

01:05So you end up with the air near the surface cooling

01:09quicker than air above that.

01:11So you have a warmer layer of air,

01:12a cooler layer of air, and then the ground.

01:15Here's what happens next.

01:16Think about the water cycle.

01:17Moisture rises, water turns into vapor,

01:19and there you have it, fog forms.

01:21There's another type of fog though, advection fog.

01:24Wind is key here because this fog is moving

01:27with the wind flow into an area

01:28rather than forming in that area.

01:31So the setup here, we have a strong breeze

01:33moving over the cooler ground.

01:36Moist air is also part of this.

01:38It moves over the cooler ground with that wind flow.

01:42Then again, you have warmer air cooling the ground below.

01:46It becomes saturated with moisture

01:47and then turns into fog.

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