Winter has come very early to many parts of Europe, with cold air spreading a long way south, bringing snow, or the risk of it, to many areas.
This plunge of cold air is believed to be the result of a weakening of the polar vortex. This area of low pressure, centred on the North Pole, has buckled. Warm air has pushed northwards, allowing cold air to spread southwards.
Snow has already fallen across the Spanish and French Pyrenees and in the next three days large amounts of snow are likely across the northern side of the Alps, bringing an early start to the ski season, but with an elevated risk of avalanches.
Snow is expected to hit the UK during Wednesday with up to 20cm of snow spreading as far south as the hills of the Pennines and Peak District.
Elsewhere, outbreaks of snow are expected to cause travel disruption across the Low Countries, and Germany.
Further east, heavy snow is expected in eastern Poland, Belarus and western Russia, with accumulations of up to half a metre. Computer predictions also indicate heavy snowfall across Bosnia Herzegovina.
There is no guarantee that the polar vortex will remain in an unstable state through the rest of the winter, but the signs are that North America could also see much colder weather in the coming weeks.
