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