Googling for some figures on the depths of winters in Siberia, I found this 1998 scientific research:

Cold related mortalities and protection against cold in Yakutsk, eastern Siberia: observation and interview study

And the Conclusion after all that learned analysis? A shocker:

People in Yakutsk wore very warm clothing, and in extremely cold weather stayed indoors in warm housing, preventing the increases in mortality seen in winter in milder regions of the world. Only respiratory mortality rose, perhaps because of breathing cold air.

Brrrr.