I thought the risk of icing reduces rapidly below -25 and is negligible below -30 and where it does exist it is in the form of rime ice. The worst icing (clear), so I was told, is between 0 and -10. However, the question doesn't make much sense to me. Rain ice from a warm front above (and above freezing) in to a cold air mass which is suddenly -30? That don't sound right
