I see what you and bluearmy mean, but if you go to 384hours, ~15 out of 21 ensemble members have a trough southwest of the UK, which is a bit surprising:
http://www.meteociel...&mode=1&ech=384
For me with the latest models, the chance of cold weather before 18 Jan looks <40%, but it's probably >50% during 20-30 Jan due to the SSW and the potential dateline convection.