I stocked up on a few mid-range "nice" whiskeys, scotches, and cognacs ($50-70 bottles) while visiting my summer cottage this summer but will likely not finish off all the bottles before I leave in a few weeks. I know they're unlikely to freeze (not totally impossible we'd hit 30 below, though 20-25 is more common; but not likely inside or for an extended enough period to really freeze them), but will their quality be affected by being between stored over the winter? Likely to have some short periods of below zero nights and possibly not getting much out of single digits during the day, at the worst; it'll usually be less severe than that (southern Maine).
I don't think that this temperature range should be a problem for the spirits. If there is a significant amount of air in the bottles, though, you might want to decant them into smaller ones to reduce oxidation.