We don’t know what the weather will be like.
There’s always this stuff about taking bets there will be a white Christmas, which used to mean at least one flake on some roof somewhere.
It’s unlikely. We have a proper white Xmas maybe once every 10 to 15 years, perhaps longer in London where it’s a city and is generally warmer.
Usually it’s grey and cold and probably wet. If you eat too much and want a walk, wrap up well.