it's actually quite warm when this occurs. Usually in March when things are starting to warm up. I think
it's when you have a warm day, followed by a cool night - it creates a kind of fog that clings to the trees -and then in the morning when it warms up again it turns really white. Shooting on days like this are usually pretty crisp, but not that cold at all. By about 10 am the sun melts the frost and it just flakes off the trees. Earlier if there is any wind.