I had the same thing happen a week ago, and it wasn't even as cold as it had been for weeks earlier. I have the ground on my harness connected to a bolt on a painted chassis piece... it was recommended that I move it to the neg. terminal on the battery. The theory being that with the expansion and contraction of the metal surfaces during wide temperature swings (cold night vs. warm engine bay after 15 minutes), that it may be causing just enough of a gap between those surfaces to lose contact intermittently. SO yeah, what Icemurder said.
I haven't switched my ground point yet, but will do it when when I have time to take the bumper off again.