Basic

Normally the train is a quiet group of a few hundred people sitting together in staunch silence, a reverent time of mourning the death of sleep. Very rarely does anyone look at one another let alone talk. 

Add a diamond-clear morning at 30 degrees, so dry that when you exhale, you become a god creating full-sized clouds, and now you have a lively, brisk group of people talking loudly and socially about the weather. 

Forget anyone talking about new inventions, social issues or some other topic, let's just break our unwritten vow of silence and discuss... the weather.