Because annual climatic and regional conditions are so variable across Germany, it can be difficult knowing what to pack for the seasons. Often the best idea is to come prepared for all eventualities whatever the season *g* I know, very general spoken ;-)
Generally, winter temperatures in the east of Germany are cold averaging minus 1°C (30°F) during January and February. Cottbus is located in the German state of Brandenburg and I've often experienced much colder winters than that, so warm clothing is needed.
Spring can be slow arriving but when it does, around Easter, temperatures soon rise. Summer temperatures in Cottbus are at their hottest during the months of July and August with temperatures reaching 25°C - 32°C (78°F - 90°F).
But in summer 2002 we had for instance very often rain, but also temperatures around 35°C (95°F). Well, it's all relative *g* It is recommended to bring light summer clothing, but not to forget an umbrella.