The pre-Christmas period is seldom affected by particularly adverse weather conditions worth worrying about, at least not in the region where you will be touring. The autobahns are generally gritted quickly should there be any frost. Snow is rare at that time in the area of the Rhine valley.
However, German law regarding the use of winter tyres is in the process of being changed and this change may still go into effect at short notice this year. Up to now, the law only stated that tyres have to be 'fit for the conditions' which is rather open to interpretation. On the other hand, requiring winter tyres from a set date in autumn to one in spring makes just as little sense if a winter is mild or if it sets in early. They are trying to work out a reasonable and enforceable alternative. It is generally accepted, however, that winter tyres are required for temperatures below 7°C.
Thanks for reminding me. I've got to get the winter tyres out of the back of the garage and fit them on our car when I get back to Germany next neek.