An area of high pressure has been centred over Europe for much of the past couple of weeks. On its eastern flank, cold air has been brought down from the Arctic. Even by European winter standards, the extent of the cold air has been exceptional.
As recently as Saturday, Moscow has experienced daytime maximum temperatures of minus 23C, some 14C below average for January.
Deaths because of the cold weather have been reported in Italy and Poland, and there have been many serious traffic accidents because of ice, snow and, across more western areas, fog.
Although it will remain cold over much of the continent in the coming days, there should be a return to "average" January weather conditions. Further snow is expected over central and southern areas.