At local shows, I get asked this question a lot.  My response is you should treat these pots as you do your others.  I ship my pots all over the place, some outside of the states.  Since every climate is different, the answer is not always clear.  If you live in Alaska, then the temperatures get much colder than the rest of the country.  Here in Portland, we get snow maybe once per year and then it goes away.  We do have our share of rain and ice though throughout the winter.  When you buy a piece that is high fired, the clay reaches vitrification which is the progressive partial fusion of clay.  As vitrification proceeds the proportion of glassy bond increases and the apparent porosity of the fired product becomes progressively lower.  This is fancy talk for the piece doesn't take on water.  So when it freezes, there is no, or little water inside to expand and break the piece.  I cannot guarantee this, so there is a risk to leaving pieces out.  As an ongoing test, I leave several pieces out all year and have not had any issues.  In the attached photo, the piece on the left has been outside all year since 2008 and the blue piece has been out since 2013.  After enduring several winters, they have remained in one piece.  So if you ask me if you should take in your pots, I would say, you should treat them as you treat your other pots.