Why does the frost only come down at dawn?

Question

Why does the frost only come down at dawn?

Answer 1

I don't know where you live; but, here in the Ozarks frost can happen way before dawn!!

Answer 2

Because if it didn't that old saying "its always colder just before dawn" wouldn't be true.  Or was that darker before the dawn?????

Answer 3

As you have already been told, dawn is the coldest part of the day. But that happens only when there is a high pressure with no wind. Then the sky is usually clear and the heat of the surface radiates toward the sky, cooling down the surface and creating an inversion, i.e. colder air under warmer one.

If there is moisture in the air, it will condense as small water droplets because cold air can contain less moisture than warm one.

But when the temperature drops under freezing point, those droplets are still liquid because they need to give away heat energy in order to freeze and they are so small that they have nearly no mass. That's how you can get undercooled water droplets and even undercooled rain.

When such undercooled droplets meet anything like the edge of a plant or flower, it will freeze immediately and show a beautiful frost rim.

Beautiful for most but extremely scary for me, a pilot. Because the same happens when such undercooled droplets meet e.g. the leading edge of my propeller or wing. Very soon the icy frost will bring my plane down.

This happened to a friend last winter here in Norway. He survived landing in the woods but his aircraft was nearly entirely distroyed. But he got it repaired at the factory in the Czech Republic and this week-end, we will go and fetch his plane and fly it from Praha to Oslo. ... luckily there is no frost at this time of the year! :-)

Answer 4

In the night temperature keeps on going down, by dawn the moisture/vapour  in the air gets solidified to form droplets

its looks like sweat.

Answer 5

as dawn is the coldest time of the day , so the tempreture decreases & resuilts in frost .