You might check the temperature specs for those tires (
www.tirerack.com). I've got PS2's and many people report that they're slippery at 40 deg F and lower. I've driven mine in temperatures well below freezing and it was ok, but it defnitely seemed to have less traction when it was cold. (the instructions from Michelin on the PS2's is not to drive in "near freexing temperatures". I'd be curious if your tires came with the same warning.