Was about to say the same, Stockholm surely sometimes gets colder than -16°C. Without looking any stats, probably -16°F (which is -27°C). For Helsinki, which not much further to the north, but closer to continental Russia, the record lows are -34°C / -30°F.

And I slept outside in temperatures colder than this, my children did, and their children eventually will. It's a matter of proper clothing.