I've accidentally discovered that naturally generated snow layer is only partially destroyed by a nuclear explosion's fallout (see minimap screenshot below). Seems aligned to quarter-chunks, sometimes to 1/8th of a chunk. Sorry for lacking report, I only stumbled across it accidentally and in a hurry. Should be reproducible easily, but just in case it has an effect, my explosion was of a metastable U238-M2 ingot.

For performance reasons, explosions only cause block updates on the very edges which saves a lot of processing time. Fixing this without causing even more lag than having block updates would be complicated as well as useless since a new explosion system is already being worked on.