Q: How and why does frost form?

A: I guess you could say that frost is the same as dew, except colder. When I pour myself a glass of iced tea in summer, humidity from the air condenses on the outside of the glass. If the glass was colder than thirty two degrees, ice crystals would form.

That’s the simple explanation, but what’s curious is when frost forms even though night temperatures don’t go below freezing.

This can happen on clear nights when grass, roofs and dark surfaced cars lose heat to the sky faster than the air can warm them. Their surface temperature falls below thirty two degrees and frost forms. This happens to dark surfaces more than light surfaces, because a dark surface usually emits heat faster than light-colored surfaces do.

If you need even more explanation,see this link:

All You Ever Wanted to Know About Frost