Hi Sandra (and other fellow travellers to the Rockies)
I live local to Heathrow, so direct from there for me.
As regards clothing, I've been following the weather for Vancouver and Calgary and currently the forecast predicts a high of 24 and low of 11 for Vancouver and Calgary has 26 and 9, so this suggests layers with a warm/waterproof jacket and of course sensible footwear.
One of my fellow commuters is from Vancouver and says the weather should be warm but could be a bit nippy first thing and at night.
Hope this helps. See you soon.
Sylvia