Most snowfall does not melt at 0 F degrees because it's too cold for it to melt.
However if the sun is shining just right then snow can melt some when it's only 0 F out.
I've had snow melt off my metal house roof when the sun was shining and it was 0 F out which was surprising to me.
But I believe what happened was that the sun was heating up the metal roof which then lead to the snow melting off the roof.
However I've also seen some snow on the ground melt when it was 0 F degrees out as well but it only melted a little.
The ground below the snow can be warm enough to allow some snow to melt.
However most snow only melts when it gets to at least 32 F or above freezing temperature.
Not much snow will melt when it's below 32 F or freezing but sometimes it can melt a little.