In late December (the date suggested by the news broadcast when Frank is driving), the weather in Inverness, Scotland ranges from 35º to 45º, which is entirely unsuitable for driving without a heavy winter coat and hat in a convertible with the top down.
When Claire is running towards Craig na Dun, the leaves of the beech trees have recently budded and the oak trees have yet to get their leaves, even though it's supposed to be mid December.