Why talk about the weather? It's something that everyone has to deal with and experience. Even if people know each other well, it's common for English speakers to start a conversation with brief small talk about the weather. It's a way to reconnect and build common ground. You can also get a feeling for what kind of mood your conversation partner is in: Is today a good day to ask your boss about taking a three-week holiday during the busiest time of year, or did s/he get caught in a downpour and still walking around in wet shoes?
Test yourself: set a timer for 2 minutes. How many weather-related words and phrases can you list?
Want to learn more? Have a look at FluentU's list of words and phrases for dealing with the weather.