What is the Rhine Valley like in terms of landscape during this time? Specifically any river cruises that run through St. Goar.
If there's snow, then I think that would be beautiful too. But it's the period in between when there's no foliage and no snow that I'd prefer not to see. I know it's being picky, but if I only have one chance to see this area of Germany, I wouldn't want to see it when there's no greenery.
Um... Trier is not on the Rhine. If you go from Trier to St. Goar, 90% of the distance is along the Moselle river.
Like the upper Rhine valley, the Moselle vally has a somewhat nicer climate than other parts of Germany, but the weather in Novermber is still rather ugly, and trees are in the process of losing their foliage. In early November, you still may see the pretty autumn foliage but towards the end of the month, it will be mostly gone.
Here's a picture taken in the Moselle valley on October 29th:
And here's one taken on November 21st:
Both are from 2011, but of course the weather in any given year may be different and shift the time of foliage shedding. All in all, October would be a better choice.
In November temperatures are falling and the days get notably shorter. Temperatures around and little below 10 degree Celsius. Although it can happen that you have a bit more at the beginning. The chances to have snow in the Rhine valley in early November are very very low. November is probably not the most pleasant time to visit this place.
There are indeed cruises at that time. With KD you can go from Rüdesheim to St. Goarshausen and back. However, compared to the high and low seasons, the winter schedule is quite meagre:
http://www.k-d.com/en/kd-scheduled-cruises/kd-rhine-timetable/
