The latest surface observations show a balmy 30F here in Salt Lake, but 10F in Rock Springs, -6 in Cody, and a nasty -24F in Great Falls.
MesoWest surface observations at ~1600 UTC (0900 MST) 31 Jan 2011
At Rock Springs, winds shifted from westerly to east-northeasterly between 4 and 5 AM MST. Temperatures began to fall ahead of this wind shift, but dropped more quickly following it. Thus, I suspect it represents the leading edge of the arctic air.