More than likely you are crossing into the jetstream, which is generally flowing west-to-east or south-to-north around eastern Nfld. I have been on several flights headed west, on descent into YYT, where the pilot warns the passengers that the upcoming turbulence will be a result of entering the jet stream.

I find our weather here often depends on which side of the jetstream we are on on a given day. If it is to the west of us we get warmer weather then when it is to the east of us!