Just how cold this arctic air mass? Here is a map of current temperatures. Note that Canada is the second largest nation in the world -- and the entire country save for a few cities on the fringes is below freezing! This map will update every hour at about 15 minutes past.

http://www.canada-maps.org/british-columbia-map.htm

And here are the current conditions for a few cities along the valley:
Williams Lake
Lytton
Bellingham

Also, for weather geeks, watch the pressure gradients -- i.e., the difference in pressure in milibars between Bellingham (BLI) and Williams Lake (YWL) -- it's the table on the upper right and most recent is on top.  Anytime that gets into the -15 to -20 range, that means there's a very strong difference in pressure between those two cities, with the pressure some 15 to 20 milibars higher in Williams Lake than Bellingham, and a strong northeast wind follows.  That's generated because cold air is very dense and thus is associated with very high atmospheric pressure.