Although the prospects of snow was forecast, this snowfall did catch many people by surprise on the 6th January 1994.
A band of rain became slow moving in a line from the Wash to Hampshire, including parts of West London. As the falling preciptation cooled the surrounding air, the rain turned to snow and this process was fastest in the areas where the preciptation was heaviest. By evening, most of the Home Counties to the north and west of London were having heavy snowfalls and this severely affected the major routes in the area especially the M1, M25 and M40 causing travel chaos. Up to 7" of snow fell in parts of Hertfordshire, Bedfordshire and Cambridgeshire. The situation was further complicated when the skies cleared later in the night to allow the snow and slush to freeze.

I don't remember that one.

A horrible wet day here. Winter 1993/94 turned into a damp squib after a promising start with excellent falls of snow in November and over Christmas. January and, more especially February, were vile months.

1994 in fact had the wettest January/February pairing on record here but then the rest of the year after that was exceptionally dry.

That's a really beautiful chart. When there is a complete lack of wind like that with open isobars any heavy rain can turn to snow even in relatively mild air. One of the best examples I've seen was, I think, in 2012 in NE england where heavy rain and 6C in the morning became heavy snow and 0C by early afternoon.