I think we all know that frost forms on certain objects before the temperatures actually get below freezing, every year. And sometimes when we are trying to hold onto our poles.
I actually was on the prow of a boat when we went through a cloud of freezing fog. It iced up my hands and I was grabbing at the rod with iced up fingers. It just took a few seconds. Ouch. But that was below freezing, I am fairly sure.
But actually this is a very cutting edge question. We know that frost forms on metal at above freezing temps. History.
Remember the mini solar system from H.S. Science class. One orbiting electron was hydrogen. Two electrons was helium.
But it appears that there is no electron orbiting. Nope. OOPS! It may be more like a cloud of much smallerstuff.
The electron forms when something intersects the cloud, or it intersects with the outside space. Complicated yup.
So when metal atoms form up in a "giant" crystal or other structure, like a line guide, they share electrons. WE THOUGHT! It turns out, they share the cloud of smaller stuff with each other. And to conserve energy (??) they share characteristics between atoms too, since it's one big cloud. But those characteristics are really where the electrons get formed and interact with other atoms.
So when a metal surface shares it's electron cloud with say hydrogen in water: it appears that the very characteristics of the metal get shared out for short distances.
Characteristics like: atoms forming up in rows to make a solid, Electron shells forming a solid rather than forming a liquid or forming a gas.
I hope this is as interesting to you as it should be.
You also might Google "condensation nuclei", or Snow-making.