This is a link (via Google Groups) to a topic posted on the uk.sci.weather newsgroup by a knowledgeable regular:
groups.google.com/group/uk.sci.weather/browse_thread/thread/7d7648c2cd655ad9?hl=en#
There's a lot of what he's posted that I don't understand, but there have been mentions on that newsgroup about the low temperature over Greenland:
www.woksat.info/etctl06/tl06-1436-e-grn.html shows -71C over the plateau, and that's the direction our weather has been coming from.