It might not happen very often, but I’ve had a journey of 120 miles where I left the house at -10, and saw temps as low as -18 within 5 miles before reaching Edinburgh, and was driving at -12 on the M8. Traffic was stopping all over the place as windscreens and washers were frozen solid and covered in dirt, and by the time I reached Harthill services they shop had almost run out of de-icer and screenwash and it was only 8:30am! When I got back home later that afternoon it was still reading -10 on the dash.Indeed - I’ve restrained from posting about Bjørn’s findings though because his winter results for the high speed Kona test was in -13°C and I’m sure people would be quick to claim that’s too extreme to be considered as a realistic worst case for the UK.
But in any event, I suspect wind is probably a more significant factor, at least unless you get to extremely cold temperatures - and as I found yesterday, strong winds (and rain) can happen at just about any time of year.
I’ve lived in the same part of Scotland for a little over 20 years and do recall many winters, often around late December or early January where there would get a week or maybe 10 days where daytime temps maxed at about -5, and night time lows were -15. Thankfully, unlike Bjorn, we don’t get this seasonal pattern reliably every year nor for the length of time that he does