Considering the Bonn City in Cologne?
A VT member wrote the following comment about visiting Cologne:
Weather by keeweechic
Germany has a moderate climate with the summers usually warm but pretty cold winters. The warmest months of the year are from May to September. The average temperature in July, for instance, varies from 16C to 20C (61F to 68F) according to the location. In January, the variation is from -1C to 6C (21F to 34F). There is no particular rainy season.