In Krasnoyarsk , the temperature dropped to the lowest level in history, -6.5 ° C, according to the Russian Institute for Hydrological and Meteorological. Previous minimum of -6.4 ° C.  was established September 27, 1988.

The Institute adds that it is a mean daily , not the minimum temperature , so you can guess that mercury bars at night dropped to below -15 degrees.
http://krolowa-superstar.blog.pl/2013/09/29/padly-nowe-rekordy-zimna-na-syberii-na-tym-nie-koniec/