When you search for a city and enable the weather filter the weather is shown in Fahrenheit. How do I change this to Celsius.
Open your terminal (Ctrl + Alt + T) and run the following command to change the temperature unit to Centigrade:
gsettings set org.gnome.GWeather temperature-unit "'centigrade'"
As can be seen in the image below, temperature is now shown in Centigrades:
Alternatively, you can use dconf Editor to change the temperature unit and all the other Weather settings from a single place.
Navigate through org → gnome → GWeather in the sidebar. Then, change the
temperature-unit and other settings as per your liking.