Germans believe that if a person does not have anything valuable to offer in a given discussion then it is better that they say nothing at all – die Klappe halten.
Klappe is a cover, lid, flap. Halten is to hold or keep shut. Germans do not consider it to be impolite if in a discussion one or more people say little or nothing. Seldom do they ask, prompt or summon those who are silent to participate.
To talk about the weather in the German context means to talk about nothing of importance, to have a meaningless conversation, to be superficial. It is a signal to both parties that they have nothing to say to each other. It‘s embarrassing for both.
