Here is what I wear in winter in Minnesota. I have ridden only down to zero degrees, however.
My helmet is solid on the top, so it provides some wind protection. It also has a face shield, but I leave it up in the dark because it is tinted.
At the army surplus store I found one of those pull-over hoods that covers the head and neck, leaving the face exposed.
Also at the surplus store, I got some cheap ski goggles. I would recommend not going as cheap as I did ($5) because a little better quality would be a little more comfortable. The next level up would the in the $20 range, and above that one could spend a lot at the fancy ski places.
If it is really cold, I wear one of those face masks that covers the lower half of the face and fastens behind the head. I can't remember where I got it, possibly out of the Brigade Quartermaster catalog, but they must be commonly available in outdoorsy stores. The nose runs a lot when one wears this. Put this item on last, because after you are warmed up you might want to take it off.
I also have a home-made item, a tube of thin stretchy fabric. I can wear it around the neck to plug up the top of the jacket, or stetch it over the head like the hood, if the regular hood is overkill.
If it is not really cold, I have a thin cap which I believe was designed to be a bike helmet liner and so probably can be found at a bike shop (mine was a gift). I wear this if the hood or the stretchy fabric tube are too much.
On the torso I wear a Tshirt and cotton shirt--the work clothes. Over that I wear one of those polar-fleece jackets. This has a high collar so it can plug up the neck. Over that I wear an unlined parka shell jacket from REI. As the temperature drops, I replace the fleece jacket with a heavy wool army-surplus sweater (another gift). The next level of cold will have me replace the unlined parka shell with a lined jacket--actually a parka-like, thinsulate coat that was a hand-me-down from my late father. A real parka would be vastly too warm. If it is dark I will wear over the jacket a yellow reflective vest, sort of like a sleeveless jacket. This adds a touch more windbreak. I never have had to go to more clothing than this, as far down as zero degrees.
On the legs, I wear the cotton docker-like pants that are the work outfit. Over that, I wear a pair of pants that are designed just for that purpose--to be over-pants. They were another gift, out of the Mass Army-Navy catalog. They are unlined. As the temperature drops, I add either long underwear, the polypropylene wicking stuff, or, again from the surplus store, some wool paratrooper pants with plastic wind shields in the thighs in place of the unlined overpants. I never go both--it is the cotton work pants with long underwear underneath and unlined overpants on top, OR the cotton work pants with the paratrooper pants on top. Once again, one must not overdress or one will get very uncomfortable.
For feet, I have a pair of insulated hiking boots from Payless Shoesource, for about $25. Usually I wear cotton socks in them. As the temperature drops, I replace the cotton socks with wool socks. The next level of coldness will have me adding those little white wicking socks under the wool socks. When there is snow, I use gaiters to cover the tops of the shoes and bottoms of the pants. This, too, has served me down to zero degrees. Sometimes the feet have started to hint that they are cold, so at colder temperatures I might have to do something else, but I don't know what yet.
The hands are a problem. Down to around freezing I wear leather gloves with wool liners from the army surplus store. For colder temperatures, I have those leather "chopper" mitten shells. Inside those are the wool liners that come with them. Inside the wool liners are a pair of hand-knitted mittens from my late aunt. For just being outside, these are good to 20 below. On a bike, with the wind chill, they are not. My fingertips still get a bit numb after a few miles, and I find myself curling up my fingers when I hit stretches of road where I don't have to brake or shift. I am still searching for better hand gear. There is some outfit in Duluth that makes super-duper cold-weather biking gloves (reviewed on www.icebike.com
) but they cost over a hundred dollars. I have tried plastic inside the leather shells as wind blockers with no success. My brother says that rabbit fur mittens work, but I have trouble with that solution on principle.
The exact temperature points where one adds, subtracts, or changes clothing probably depend on individual circumstances.
Hope this gives you some ideas. Riding to work in winter is fun because people seem to think it must be a miserable thing to do. Except for fingertips, I never have been cold riding a bike in winter, because I tend to overdress. If anything, I am a little too warm.