The too cold for snow is based upon most cold being from high pressure in the UK at least and with that you don't get the moisture in the air - snow in the UK i

The too cold for snow is based upon most cold being from high pressure in the UK at least and with that you don't get the moisture in the air - snow in the UK is mostly a clash of warm/cold are battling from Europe and the Atlantic. Hence we see most snow with good cold easterly and battling lows comming in hitting that cold air. But as a child I too always questioned the saying "too cold for snow", the high pressure aspect is why as a rule of thumb, it works for the UK, but always exceptions to rules.