Heavy snowfall has already affected much of the UK

Heavy snow is forecast across parts of the UK during Tuesday, with several severe weather warnings in place.
The Met Office says Wales and most areas in England are at risk, with up to 30cm (12in) possible on high ground.
Extreme weather warnings have been issued for north-west England, Yorkshire and Humber, the Midlands, east and south-west England.
The Met Office says transport services and power supplies may be affected. Icy roads are also a problem across the UK.
Severe weather warnings are in place for icy roads in Strathclyde, Tayside and Fife, central and south-west Scotland and Lothian and Borders.
Sub zero temperatures
There have been some snow showers around the Moray Firth and down the east coast to Aberdeenshire.
Inverness Airport in the Scottish Highlands was closed because of bad weather but reopened at 1130 GMT.
Train services to and from Glasgow were also affected by the conditions.
NHS Grampian said between 20% and 25% of people arriving at the Accident and Emergency department at Aberdeen Royal Infirmary since Christmas Day had fractures, compared to about 10% normally.
The majority of these were wrist and ankle injuries, which are common in falls.
Temperatures plunged to -18C (-0.4F) at Braemar in Aberdeenshire - the coldest night so far this winter.
At Tyndrum in Stirlingshire the mercury dropped to -17C (1.4F), while at Strathallan in Perthshire it was -16C (3.2F).
Fog caused travel disruption on Monday in Liverpool

The Welsh assembly government said contingency plans were ready to keep main roads open and that its stock of salt for motorways was available as a reserve for councils.
Passengers planning to travel from Cardiff Airport have been advised to check whether flights are running on schedule.
The BBC's Weather Centre predicted the snow in Wales and southern England could be mixed in with spells of sleet and heavy rain.
BBC weather forecaster Laura Tobin said rain was making its way across England and Wales from the south, turning to snow across Bristol, Bath, the West Midlands and central part of Wales.
The Met Office said the wintry conditions would continue in parts of England and Wales into Wednesday.
New Year's freeze
The Highways Agency is warnings drivers throughout the UK to take care in the next few days as many roads are likely to be icy.
Further snow and ice are also forecast for New Year's Eve.
Ice has been a problem in many parts of the UK over the Christmas period after heavy snow and sub-zero temperatures.
Householders have been taking action to clear paths, pavements and roads, with sales of salt soaring in supermarkets.
Morrisons said sales of its 1.5kg (3.5lb) bags of cooking salt have increased by almost 400% compared to the beginning of last week.
While Asda said sales of salt have increased by 300% in the past week.
There has also been a brisk trade in cat litter, which can be used as an alternative to grit, with Sainsbury's reporting a rise of 20% compared to this time last year.
DIY retailer B&Q said it was experiencing an increased demand for wellington boots and shovels, while sales of rock salt soared 900% on the previous week.
There are more than a dozen rail engineering works taking place on Tuesday, but Network Rail said more trains were running over the Christmas and New Year period than in the festive period last year.
Seven incoming flights were diverted and 10 outgoing flights cancelled at Liverpool's John Lennon airport on Monday after visibility on the runway was reduced to just 300m (984ft).
Meanwhile, it has emerged that a man died after slipping on ice while visiting his mother's grave on Christmas Day.
Jimmy Halpin, 53, suffered serious head and neck injuries after he fell in Urmston Cemetery, Greater Manchester, while making his annual visit to lay a wreath on the grave of his mother, Mary.