I recently planted the day after an ice storm with highs in the mid 30's. As long as the ground is not frozen and you can dig, I think it would be ok to plant. I would suggest putting a layer of mulch around the tree to insulate the ground around it just to be sure the roots don't freeze.

Otherwise, depending on how large the roots are, stick it in a 5 gallon bucket and fill with potting soil or that cheap top soil and moisten so the tree has water. Just don't over water. You may need to drill a hole in the bucket just in case. I kept my mulberry bare roots in this manner for 3 weeks. Keep in a cool, but not freezing place.

It may not be such a dire situation, since you said the tree is fully dormant. It would probably do fine planted during the cold weather as a result. If you want to play it ultra safe though, you could do the second method -- probably no need to pot it though, just keep the roots bagged and somewhat moist (after all, most bare root trees spend quite a bit of time this way before being planted).

Plant it. If still fully dormant and hardy for your area, it won't mind the cold at all.

Thanks for the input. The deed is done and the tree planted, which I suppose was my preferred choice to begin with. Better to let nature do what it's supposed to. Too bad the weather can't decide for itself! What a way to begin March.