AccuWeather's Melissa Constanzer breaks down how dew forms.
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00:00It's okay. It's okay. Don't worry. My neighbor's house wasn't on fire. That was a spectacular May
00:06morning a few years ago where I captured dew burning off as steam. It's the evaporative
00:11process that dries up the grass and so many other surfaces. Now, many roofs can heat up quickly in
00:17the morning sun, so a lot of water is trying to evaporate quite quickly, too. Thus, we can actually
00:24see it as steam because there's so much water coming off of it. But how do we even get that
00:28glimmering coating that you see there of dew to form in the first place, right? Because it has to
00:34come from that moisture. Well, there's a little bit into that process. First, you have to understand
00:39what happens as we go into the nighttime hours. We get what we call radiational cooling. So on a calm,
00:45clear night, this is when it happens to the greatest extent. If there's a little bit of a
00:50wind, we can have more mixing in the atmosphere. But ultimately, on a calm, clear night, we watch
00:54that surface temperature. As we go throughout the day, the sunshine comes out. And of course,
00:59you have the warming that takes place. So we know those numbers will go up during the day. The sun
01:04is heating the ground. And of course, all the air then is also absorbing some of that warmth as well.
01:09So that's why we can get into the 70s, for example, for a spring afternoon. But then with those clear
01:15skies and really no wind at night, all that heat rises and it cools very quickly. The surface is no longer
01:22warming. Therefore, it has to cool down into the 40s. Knowing that, let's talk moisture. Because if we
01:28have a dew point in the 40s, that's when we know that dew will condense. Then you can see as we go
01:33through the nighttime hours, that temperature drops right to about near that dew point. And then once we
01:39get it to that dew point or around it, we start to see the dew form. And that's how we get dew.