A somewhat different but related phenomenon may be observed on a car
parked outside overnight when the temperature hovers around freezing and
it is fairly moist. Moreover, there is no wind. Under these conditions
one can find that the front and rear windshields are lightly iced,
whereas the side windows are wet but unfrozen. I assume that the colder
air falls to the ground so that by the side windows it is slightly
warmer. However, for the windshields the "ground" is the hood or rear
trunk and is just that much cooler.
I observed it again this morning at about 6:00 with the temperature
about 37 degrees.