How dew forms on grass, trees

6 Storm Team Weather School

KNOXVILLE, Tenn. (WATE) – Have you ever looked down and touched the grass in the morning and noticed it’s a little bit wet, well that wetness that you’re feeling on the grass is called dew. Let’s talk a little bit more about why that forms.  Let’s start off with radiational cooling, that’s basically the cooling of the earth’s surface overnight. During the day the sun heats the earth and you’ll notice that surface temperature slowly begins to rise.  At night this is when that radiational cooling takes place, the heat rises it cools the surface and the cooling does take place quicker under clearer skies.  Now let’s talk more about how that will lead to dew.  Again the sun heats the earth during the day, once we get to the nighttime hours that heat rises and the air above the surface slowly begins to cool but as that air is beginning to cool the cooling forces that moisture onto the ground and that’s why we’ll see that liquid water or called dew begin to form, in above freezing temperatures so now when you look down and touch the grass in the morning and see that dew you’ll know how it forms. 

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