Useful information : When to go, Getting around...

Germany’s weather can best be described as unpredictable, whatever the time of year. That said, the most reliable period in terms of climate is from May to October. At this time, the weather is mild, even hot in the summer. Very heavy rainstorms can however occur. Whatever the case, it is the peak season for hiking in the Black Forest. On May 1, make a beeline for Berlin and its immense street festival, Myfest. In August, suited to swimming in the lakes, the mood is more sedate at the Bayreuth Richard Wagner Festival. In October, the tourist season comes to a boisterous close at Munich, during the Oktoberfest, the most popular beer festival.
The period from November to April, often windy, cold or snowy depending on the region, is not ideal to explore Germany, unless you ski, in which case, head to the Alps. One exception however, the month of December, whose numerous Christmas markets make it well worth the trouble of defying the cold. The markets of Hamburg, Nuremberg and Dresden are the most famous.