This winter has been pretty mild so far here (Chicago). Last night though, the temp dropped and today we are expecting a high in the mid 20s. It also snowed a little bit - a good dusting is all - but I would think that that could lead to ice in the roads and on the lakefront path.
Do you use studded tires for just a drop in temperature with the possibility that you might hit an icy patch or two, or do you wait until a few inches of snow or what? I'm guessing the roads in Chicago are kept pretty clear and salted regularly, but this will be my first winter here so I don't really know what to expect.