I've used my DSLR down to -5°F (-20°C) without problem for full days.
Some mental notes I keep:

1. Keep the camera at ambient temperature. If it's snowing or snow gets blown/falls from trees on the camera it will not melt and cause problems. This suggestion is contrary to what many people suggest, but I'll stand by it since I shoot outdoors and have experienced snow issues.

2. Battery capacity is reduced when batteries are cold. Keep extra batteries inside your jacket to keep them warm. I didn't have any problems with a single battery taking under 100 shots per day. If you do time exposures for shots of aurora, you may want to use a warm battery.

3. As many state, the biggest problem is taking a cold camera indoors. Since the dew point indoors is much higher than the dew point outdoors, the camera will instantly fog - lens and body. If you place the camera in a air-tight bag while outdoors and let the camera warm up to the indoor temperature while in the bag for 45 to 60 minutes, condensation won't be a problem.

4. Gloves: Wear liner glove(s) under your heavier gloves. If you need finger dexterity to operate the camera, remove the heavier glove and the liner glove will allow the dexterity you need and keep your hand(s) warm enough for a short period. When removing the heavier glove, place it inside your jacket to keep the glove warm. You will enjoy the warmth after the shot. There are "photography gloves" with a flip finger tip that allow you to expose your finger tips for photography use. You could wear a lighter glove and use a hand warmer packet(s) in the glove.
   This is a good time to visualize your shots to reduce the setup time and number of shots whilst keeping comfortable.

5. Snow conditions will fool the light meter and create underexposed images. I generally use exposure compensation (either mentally or use the exposure compensation setting on the camera) set to +1 to +2 stops to make the snow white. The histogram is a wonderful tool for setting up exposure.