Not only outside, -2F at 8:30 AM; but inside too, 55F at the same 8:30 AM. It turns out our twenty-year-old furnace decided during the night that it didn't want to see another birthday. Of course, we didn't know of that final decision until after the repairman had come out to look at it. The fan had some issues, as did the circuit board, both of which could be fixed. Apparently the furnace has decided it would rather have cracks in its main and secondary heating chambers than reach a legal consumption age.
(With any luck the temporary fan fix will last until tomorrow. Right this minute, it isn't looking as likely as it was at noon. I think we might know around eight tonight.)