> 20 years ago it was unusual not to have snow for Christmas and New Year.

This is one of those widely spread Mandela effect-style misconceptions.

The chances of a white Christmas in the UK are around 10%, and depending where you are in the US [0], especially if you consider the population density not pictured in that chart, even lower.

Humans generally hugely overestimate how often a white Christmas actually happens due to selection bias.

[0] https://en.wikipedia.org/wiki/White_Christmas_(weather)#/med...