The winter of 1968/69 was the coldest winter the province has ever seen in the north. Lower Post in the north averaged -30.2C for the winter, which is a colder winter than it has ever been in Alberta, Saskatchwan, Ontario, Newfoundland, and until 2015, Quebec (Parc National Des Pingualuit averaged -30.2 in northern Quebec in 2014/15, shattering the old provincial record).
By comparison, the coldest winter ever recorded in Whitehorse, also in 68/69, was only -23.7C.
The winter of 49/50 was the third most extreme winter with a mean temperature of -27.87C at Smith River. In addition to 1968/69, Lower post edged this again in 71/72 with a winter average of -27.93C.
BTW, the coldest Spring, the coldest Summer, and the coldest Fall ever recorded in BC occurred in the 1955.