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Under what conditions does the windshield of a car freeze even if the outside temperature is above freezing?

It is not clear whether this is related to the question why bridges freeze with non-freezing outside temperatures (see related topic), as I did not see an explanation in terms of radiation there. It indeed seems that electromagnetic radiation is the culprit for windshields, which would predict that this phenomenon can only occur with an open sky. Does anybody know whether this is true?

And why does ice only form on top of the windshield and not on the metal surface of the car? Is this because heat is conducted much faster on the metal surface?

user40076
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2 Answers2

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The outside temperature may be above the freezing point but with a clear sky radiation from the car can escape outside the atmosphere. There the temperature is very low, so energy is transferred away from the car. What happens depends upon the material. The windshield is a bad conductor of heat, so radiative energy losses are not easily compensated by conduction from other parts of the car.

Urgje
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This can happen if the windshield itself has a lower temperature due to earlier freezing. This effect can also be seen in freezing rain: Air producing rain is advected over frozen ground and suddenly the traffic is in trouble.

Metalbeard
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