LOL! I started out yesterday in shorts, figuring that it would warm up as the sun rose. In the few minutes that it took to drive to the county offices in Martinez, my windshield started to collect ice as I drove, with a clear sky! - That's what I call Global Warming.
Yesterday, we had heavy frost all over.
It was not there at dawn and came later. We had the same over all effect that happened to your windshield while driving.