Much of Britain and Ireland has been blanketed in snow as freezing Siberian weather dubbed "the Beast from the East", disrupted the travel plans of thousands.
Hundreds of schools were closed on Wednesday and there were delays on roads, railways and at airports on one of the coldest days Britain has experienced at this time of the year for almost three decades.
Temperatures fell to -12degC in some rural areas while Britain's weather service warned of up to 40cm of snow in higher areas of Scotland. Ireland could see its worst snow since 1982.
"It is the coldest air we have seen over the UK at this time of the year since around 1991," says Becky Mitchell, a meteorologist at Britain's Met Office.
"It is all tied in with the Beast from the East."
The cold spell has been caused by a jump in temperatures high over the Arctic, known by meteorologists as sudden stratospheric warming, which has weakened the jet stream that brings warm air in from the Atlantic to Ireland and Britain.
"The jet stream weakens and so we tend to get a strong easterly flow of air and that air is really originating right from over in Siberia - so very dry, cold continental air," Ms Mitchell said.
Across London, there were severe delays on public transport.
Ireland's weather service issued a status red warning - the highest level of alert - for five countries in the east, including the capital Dublin after heavy overnight snowfall led to accumulations of 5cm to 10cm.
Total snowfall may reach 25cm by Thursday, it added, prompting the closure of many schools and universities. Business advised workers to stay at home with some roads inaccessible and public transport operating a limited service.
Runway operations at Dublin airport were suspended early on Wednesday with a number of flights cancelled and others diverted before the snow was cleared shortly after 7.30am (local time) to allow services to resume.
The weather also affected flights in Scotland with Glasgow Airport temporarily suspending operations to clear runways following heavy snowfall.