snow/snowing

Hi, may I ask for an advice?

which is correct

It will snow on Christmas.
It will be snowing on Christmas.

is there any rule for it?

thank you vey much
M

There is very little difference between these two phrases. The second emphasises the action a little more.

Note the preposition usage:
It will snow at Christmas/It will be snowing at Christmas.
It will snow on Christmas day/It will be snowing on Christmas day.