Hey John,
I bike from -16C (3F) and up, the ride is about 12.5km's each way. For weather down to around -2C (35F) I wear a jacket and sweater, the sweater is just thin cotton and there is probably something better, and the jacket is just a thin waterproof shell, I bought it based on its stretch rating from a climbing website but it is an outdoor research ferrosi and is great. Steep and Cheap had a good price when I bought it.
When I get to the office I'll hang up the jacket and sweater which usually has a bit of dampness to them, and would reccomend having at least a couple sweaters to switch up if your biking to work everyday, you may find you only want to wear a sweater one day, or a couple days before it needs to get washed. I should probably find something better for sweating in multiple days, but it works and they have a shower at the office.
I also wear a thin stretch cap to keep the sweat out of my eyes, I've got like 5 or more of them and cant bike without them
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For Calgary if its -2C in the morning , it will probably be anywhere from +5C (41F) to +18C (65F) on the way home, and then I'll wear just the sweater, or jacket or neither, but you gotta get used to finding the right combination so your not sweating too much on the ride, thats just trial and error, and when you get it right you'll still be sweating when you get to where your going. I also made a habit of buying brightly colored biking gear, so as I take layers off Im still very visible to traffic. Most of my office under shirts are brightly colored too. A couple close calls with vehicles and it's easy to see why.
The nice thing about the ferrosi jacket is it also bundles up small and fits nicely into my pannier bag. Also a nice upgrade over a backpack or courier bag, which will cause you to sweat more on your back.