So, I was just playing survivor.. and Halloween event is coming up.. and its snowing? like what, its been doing that for continuous rounds.. I'm not sure if this is some rare type of effect that comes on now and then.. or its just map-slide mixed with the event.. I have no idea..
http://i.imgur.com/3gNeRJs.png

Hmm it may have glitch out were other people seeing it?

happened to me once, too
just restart the game and the snow goes away

Do you know if there was a mod in the room?

No mod..

maybe its preperation for christmas :D

Christmas is long far away bro.. and Halloween is coming up soon -.-