KNOXVILLE, Tenn. (WATE) — On a cold early morning, while scraping frost off your front windshield have you ever wondered how frost forms.
It has to be with a process called radiational cooling which typically occurs at night. During the day the sun is heating the earth and then at night, the heat rises from the surface, cooling the ground. This process happens faster under clear skies because clouds provide a blanket keeping the heat on the ground.
As the air above the surface begins to cool, the cooling forces moisture to develop on the ground and with freezing temperatures the moisture freezes creating frost. For frost to form the surface temperature must be between 30° – 32°F which is the temperature needed for water to freeze.
However, the air temperature can be a little bit warmer around 35° to 37°F. This is because the surface cools first and faster than the air above it meaning the surface can be right at freezing when the air is not quite at freezing temperatures.