What would cause water to freeze on my cars when the air temperature is 42°F?
Jorganos did not get it quite right. The reason that cause frost to form is mainly due to heat radiation, much like the way the sun transfer its energy onto earth. When the surrounding temperature is low enough, the surface of your car would lose heat to radiation and drop below freezing point, which induces frost to form. This phenomenon is espeically active on a clear cloudness night, even when the temperature is not near freezing point, in which the heat radiation shoots straightly into space without returning. To keep the frost to the minimum, either put a cover on the car, or park in the shaded area.
