Q - How do I switch from Fahrenheit to Celsius?
A - That is done with a console command in game. Press F1 to bring up the console then run the command: stu c






how to change from Celsius or Fahrenheit unit of temperature.

open the console and type 
‘settempunit c’ 
or 
‘settempunit f’ 
to set the game to use Celsius or Fahrenheit unit of temperature.

The game will remember it, so you have to type it just once.

hope it helps, have fun.