Its been at our just below freezing since at least 10pm. If the trail is frozen YOURE GOOD TO GO.
I'm not sure why it's made into such a big deal by some people (Yes, I participate in trail days.) You show up for your ride and if it's mess going into it, you just cut your ride short. If it's not a mess, you ride on. Conditions change so rapidly you never know what you're going to get until you get out there.
Have a good ride, Green Epic.