Leaderboard updated!
Welcome to the Challenge both @scorps and @Renni-Aire 
Thank you both for entering 
Paul, much as we’d like to accept the car dashboard as a credible source, we’d like the source of the -5C° or below to come from AirData or UAVForecast (purely because they’re drone related sources!) However we would accept any other weather provider web site (Wunderground, BBC, MetOffice, etc).
If we were to accept the dashboard as proof we’d open the flood gates to people sharing temperature screen shots from the smart watches, their DIY weather stations, their neighbours cat, etc 
If you can get a verified source of -5C° or below, please do post the photo you took here in this thread and join the Winter Treasure Hunt - there’s still plenty of time left! 