What to take???????

I leave in 2 days and cannot for the life of me figure out what clothing will be appropriate for Alberta in May. I remember the year I took jeans, T shirts, fancy dress up stuff and the temperature never dipped below 28 C.Then last year when I brought Capri's, shells and a cotton sun dress and it snowed. I can no longer borrow from my daughter since she has found the figure I have always dreamed of and now shops at the other end of the rack.. so what I bring I am stuck with. I'm thinking the basic black and white layer look is the best deal. Allah!!! I hate packing.