Frying a turkey while snowing
There's so much heat around a turkey deep-fryer I wouldn't see how light or medium snow would affect your cooking. Any snow is going to melt and probably evaporate before it comes into contact with any hot oil, and any that makes contact will be gone in a flash. I've barbequed in 20 below and in snow, all that it really means is that you need more heat. 

My main concern would be wind, not snow. Wind will blow much of your heat away, and a really stiff wind could blow the whole rig over which would ruin your day. You want to set up the frying rig in a spot that is out of the wind. Light and medium snow really isn't an issue.