Heavy snow is causing treacherous driving conditions in Scotland and parts of northern England and Wales.
Blizzards overnight shut Scottish airports, while in Glasgow about 3,000 stranded clubbers had to seek shelter. Motorists were advised not to travel.
All schools in Clackmannanshire are expected to be closed on Monday.
Thousands of homes, mainly in rural areas in Dumfries and Galloway, Ayrshire and Lanarkshire, are without power because of downed cables.
Scottish Power said it was hopeful that supplies would soon be restored to affected customers.
Forecasters say snow, accompanied by gale force winds, will move eastwards and ease by night, although they expect more falls on Monday evening.
Police across Scotland advised people not to travel unless it was absolutely essential, and there was a similar message from rail operators.
The M74 motorway, which links Scotland and England, was closed to northbound traffic at Johnstonebridge, while the A9 to Inverness was shut in two places. Both routes are now open again.
Edinburgh Airport reopened shortly after 0930 GMT on Sunday, and Glasgow reopened at 1600 GMT. Two flights from the US had to be diverted to Belfast.
In east Ayrshire, a heavily pregnant woman was airlifted to hospital by the RAF because her ambulance was struggling on snowbound roads.
Shirley Anne Hodge, 18, later gave birth to daughter Skye at Ayrshire Central Hospital in Irvine, and is doing well.
Two climbers were taken to hospital after spending the night stuck on Ben Nevis in freezing conditions.
The Met Office issued a severe weather warning and said the winds could mean there may be as much as 10 to 20 centimetres of snow in some places.
Snow also fell in Liverpool, Manchester and Newcastle but police said light traffic helped keep disruption to a minimum.
Most central and eastern areas were experiencing a dry but cold day, with temperatures of about 3C. The South, South West and Northern Ireland were seeing some showery rain and slightly higher temperatures.
A front from the west, combined with cold air from the east, brought the snowy weather, but will begin to ease off.
BBC Weather presenter Peter Gibbs said strong winds could result in snow already on the ground causing drifts, especially across Scotland and northern England.
"It will turn very icy overnight in the snowy areas, with further drifting also likely," he added.
Cold easterly winds are forecast to set in across the whole of the UK during the week.
"Another spell of heavy snow is expected later on Monday, affecting mainly northern England and southern and eastern parts of Scotland," he said.
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