Frost can form because the ground surface is cold enough.

Frost had formed on various parts of the ship things.

But her skin was so cold that frost formed on it as she pulled back from him.

Frost was forming on the inside of the telephone box.

Another possibility is that the bright frost has not yet formed.

For the frost was forming on us, or so it seemed, as our skin chilled toward death.

While I smiled and nodded to her, frost formed on the back of my neck.

Near the floor, frost had formed on the inside of the thin-glass.

Dix was amazed frost didn't form on the inside of the window.

Roger's eyes were closed and frost had formed on the lids.