-7°C (20°F) is PERFECT for winter. That's pretty much the ideal winter temperature. I'm not kidding - warmer than that and the snow turns wet and difficult to shovel, and if it gets too warm so the snow starts to melt, there will be ice later when it freezes again, and ice under snow is officially no fun.

Not sure what the temp is here now, but it was -10°C (14°F) which is also a very nice temperature, this morning. I don't really like it once it gets below, say, -12°C. We had -18° which is about 0°F most of the weekend, and it's going to move in that direction again, I think.

http://www.wbuf.noaa.gov/tempfc.htm is your friend