Just to add, my last visit was mid-May 2013. All the lakes were still iced over. Lake Louise was in full swing, however ice skating was over for the season due to melting ice. The road to Lake Moraine was closed by deep snow (and barricades).
Many of the campground sites were not open yet (still several feet of snow).
The little town Banff itself was all open, in a sort of transition. There were a few winter tourists still lingering.
It was warm (60s) during the day and a bit chilly at night. It did not snow at all while I was there.
