Frost On Roof Above Freezing

Something i implied above but didn t say explicitly is that when frost forms on the roof the roof is below freezing.

Frost on roof above freezing.

1 initially the air and the car are at temperature 37 f and the dew point is 35. Low temperatures overnight were generally in the. We had a chilly start to the day with frost in many countryside locations. On a long cold spell these objects will cool down to below 0 celsius.

The plot below shows a 24 hour trace of the temperature measured at 0 5 meters above the ground in blue at 2 meters above the ground in red and at 3 meters above. Ice at least at atmospheric pressure cannot form above the melting point of water 0 celsius. In other words the sequence might be as follows. That is how we get a frost without a freeze.

How can that be. So the air can be above freezing and the surface of your car or the roof of your house can be colder than the air and colder than freezing causing a frost even though the air temperature is above freezing. Mon 06 oct 2008 19 38 20 gmt frost at 35 degrees. Look at the entirety of your roof is the frost melting unevenly and not due to the sun s heat.

2 the car roof cools radiatively. A lack of frost can indicate that heat is leaking out through your attic space onto the roof and melting the frost. Frost is a thin layer of ice on a solid surface which forms from water vapor in an above freezing atmosphere coming in contact with a solid surface whose temperature is below freezing and resulting in a phase change from water vapor a gas to ice a solid as the water vapor reaches the freezing point in temperate climates it most commonly appears on surfaces near the ground as fragile. The phenomenon of water freezing on objects like the ground parked cars motorbikes etc is due to thermal inertia.

So how did ice form on the roof the frost on the car effect is not just due to temperature inversions. The radiative cooling effect is strong enough to lower the temperature of surfaces exposed to the sky by several degrees below the ambient air temperature. So ice can form even if the temperature of the surrounding air is above freezing. 1 initially the air and the car are at temperature 37 f and the dew point is 35.

Have you ever wondered why frost can form on nights when the temperatures only fall to 36 or 37 degrees. Something i implied above but didn t say explicitly is that when frost forms on the roof the roof is below freezing. As it cools below 35 degrees water condenses on it. If the dew point is below freezing the water vapor condenses as ice freezing as frost.