One of the most common questions you will get as a meteorologist is "Can it be too cold to snow?". Or, when the mercury plummets, people confidently tell you that it's "Too cold to snow".
To understand this phrase, you need to understand that snow needs two things... temperature and moisture. When temperature decreases, so too does the maximum capacity of water vapour which the air can hold.
Therefore, colder air will have less water vapour available within it.
During the winter months, the coldest air across the UK will tend to come from the East. This continental air is cold and also very dry which means that whilst it would be cold enough to snow, there is a distinct lack of moisture in the air in order to actualise it.
That said, if a trough develops within the air mass which causes uplift of the air, then snow will form within the colder air, especially as air higher in the atmosphere will be warmer and thus have more water moisture. Snow can also develop across Eastern parts of the UK where low level moisture is picked up across the North Sea.
If the air is truly cold, say around -50c then it is unlikely that there will be enough available moisture in the air in order for snow to form, and at absolute zero (-273c) all air and water vapour loses its molecular energy and therefore snow would be impossible.
But, if we look at some of the coldest charts at the moment :-
The corresponding snow/rain chart shows us :-
That it is rarely too cold to snow, but simply too dry.