I’ve put together a few top 10s of stats for Wanstead, St James’s Park and Heathrow for the month of December.
Probably most notable is how the month in 1978 lurched from being very mild and wet to very cold in under three weeks later, setting up one of the coldest-ever winters.
Some national UK December values according to TORRO
Hottest: 18.3C Achnashellach – 2nd 1948
Coldest: -27.2C Altnaharra, Highland – 30th 1995
Wettest: 199.1mm Dalness, Highland – 17th 1966
Here’s a couple of graphs showing the maxima and rainfall. Notice the spike just before Christmas day which reflects the singularity which has an 84 per cent probability.