Whenever we talk about important decisions, he always tries to sidetrack the discussion by mentioning the weather.

sidetrack 是由 side（旁边）和 track（轨道）组成的复合动词，字面意思是"使偏离轨道"，引申为"转移话题"或"使偏离主题"。在句中表示通过提及天气来转移原本关于重要决策的讨论。