I remember travelling in a bus that had frost on the inside of the windows on my side of the bus, but not on the other, sunny, side. Then our route within a small town turned us so my side was in the sun, and the frost melted quite quickly. Finally, we left the town and my side was away from the sun again - and I had the interesting experience of watching those frost ferns form, quite rapidly: an ice nucleation point shooting across the film of water like a little speedboat leaving a wake of a long thin linear ice crystal, curving gently because there's no reason why it shouldn't; then side branches doing likewise, each starting at 60° to the original line. Beautiful.
Poland, December 1978. -25°C.