On a clear still night heat energy radiates from surfaces on the Earth in the form of longwave radiation. This infrared (heat) energy effectively radiates through the atmosphere to outerspace. As a result the surface temp of a car at night may be at or below the FP, when the OAT is actually 4-5 deg. C.
During daylight the opposite occurs and shortwave radiation, in the form of visible and ultraviolet light from the Sun, is absobed by the Earth and the surface temperature of the car may, under certain conditions, be warmer than the OAT.
Presumably the longwave radiation that takes place at night must equal the shortwave radiation during the day or we'd have a big problem..!!