Blizzard conditions are sweeping Britain, with snow falling as far south as London and dozens of flights grounded, amid coastal evacuations because of a flood risk.
Thundersnow is expected to bring up to 7in (20cm) of snow in parts of the UK, with the worst weather during the evening rush-hour.
Despite a respite from the rail strikes, London could still come to a standstill as snow began to fall in the capital on Thursday evening.
Motorists and ferry passengers are also facing disruption while some schools have been closed due to the bad weather.
Meanwhile, dozens of seaside evacuations are under way amid a flooding threat from storms and high tides.
The Environment Agency warned that coastal communities in Lincolnshire, Norfolk, Suffolk and Essex should be prepared for large waves and possible flooding.
More than 40 flood warnings have been issued and the Army has sent 100 soldiers to Skegness, Lincolnshire, where they began evacuating some of the 3,000 homes in low lying coastal areas that are most at risk from flooding on Thursday afternoon.
Meanwhile, police officers were going house-to-house in Jaywick, near Clacton-on-Sea, on Thursday afternoon to warn people that a full evacuation plan is being implemented in the face of rain and high winds, which could lead to floods.
Officers will be informing residents that from 7am on Friday, they will be taken to a rest centre at Tendring which has been set up by the district council, where they and their pets can stay until it is safe to return.
It comes as communities along the east coast of England are being warned of the risk of large waves and possible flooding as gale-force winds combine with high tides.
Wintry weather has already hit Scotland, Wales, Cumbria and Bradford and is expected to move across the UK during Thursday with temperatures plummeting to -10C in areas.
Heavy snow was lying across Scotland, Northern Ireland and parts of England on Thursday.
At Heathrow Airport, 80 flights were cancelled as a forecast of snow and windy weather is expected to impact on services while four flights were cancelled at Gatwick Airport.
Severe weather warnings have been issued by the Met Office across swathes of the country for high winds, snow and ice.
The Met Office said there was a chance of thundersnow - which is similar to a thunderstorm, except snow falls instead of rain - in some areas, but the weather warning applied only to snow.
The Met Office said there was a chance of thundersnow - which is similar to a thunderstorm, except snow falls instead of rain - in some areas, but the weather warning applied only to snow.
Paul Gundersen, chief meteorologist, said: "Most northern areas are very likely to see snow showers at times over the next few days, but the situation over the southern half of England is more complicated.
"Southern counties of England and Wales can expect a cold and wet day with some heavy rain on Thursday, but there's an increasing chance this will turn to sleet or snow, especially over hills, during the afternoon and evening.
"There is a chance of snow settling bringing disruption to transport during the evening rush hour and possibly interruptions to power supplies, this more likely across East Anglia and southeast England. As skies clear on Thursday night it is likely to become icy in many areas."
Daytime temperatures are likely to be around 2 to 5C, but the strong to gale force winds will make it feel much colder. Temperatures could dip below -10C over snow cover in rural areas.
Rain will move eastwards across the south and may turn to snow later, which will then turn to ice.
The heaviest and most frequent snow showers are likely across northern and western Scotland, Northern Ireland and around Irish Sea coasts, but eastern coasts will also be affected at times on Friday and Saturday.
There will be gales that could lead to temporary blizzard conditions as well as a risk of hail and thunder in some locations.
Mr Gundersen added: "Forecasting snow is always challenging and there's often a fine line between whether it will rain or snow in a particular location depending on slight changes in air temperature. Keep an eye on the forecast and warnings for your area for the latest information."
On the east coast of England, the Environment Agency warned gale force winds combined with high tides could result in large waves carrying dangerous debris through Friday and into Saturday.
The conditions are also expected to cause traffic disruption and could affect properties on the coast.
Mark Sitton-Kent, national duty manager at the Environment Agency, said: "Gale force winds and high tides are likely to create large and dangerous waves along parts of the east coast on Friday and Saturday. These conditions could also cause flooding to coastal roads and could impact properties.
"We understand that powerful tides can be dramatic, but please do not put yourself at unnecessary risk by going to the coast for a thrill or to take pictures. Please do not drive through flood water: just 30cm of flowing water is enough to move your car.
"We are prepared to take action wherever it is needed. We have moved resources and equipment to the coast and the Army is on standby to assist if needed."
Environment Agency teams have moved 5,200 metres of temporary barriers and 25 pumps to depots and towns including Newcastle upon Tyne, Blythe, Great Yarmouth, Chelmsford, Rye and Trustthorpe and South Ferriby in Lincolnshire.
The Hull tidal barrier will be operated on Thursday evening, while all east coast flood gates have been closed, the agency said.
On Friday, the cold weather is expected to continue with snow showers will becoming more isolated.
Prof Paul Cosford, director for health protection and medical director at Public Health England, said: "The Met Office is forecasting a spell of colder weather, with likely snow and icy conditions.
"Think now about what you need to do to prepare: if you need vital medicine or food get it before the bad weather arrives. People with underlying health conditions, very young children and those aged over 65 are at greatest risk, so think what you can do to help others.
"Keeping your home heated to at least 18°C, wearing lots of thin layers instead of fewer thicker ones, and if you have to head out using footwear with a good grip are all ways to deal with this weather and stay well this winter."
The Energy Networks Association has reminded people they can call 105 - the new, free national phone line - if the weather damages their local power network and affects their electricity supply.
Gatwick Airport has advised passengers to check the status of their flight with their airline and apologised for any inconvenience.
A spokeswoman said: "As a result of the forecast of snow and ice today, some route restrictions have been put in place by air traffic control that may cause some delays and cancellations to flights."
British Airways (BA) flights were among those affected at Heathrow.
A BA spokeswoman said: "We're sorry that some of our customers' travel plans have been affected due to the forecast snow at Heathrow, which will lead to a reduction in the number of aircraft which can land or take off from the airport.
"For safety reasons, Heathrow Airport, air traffic control and all airlines have agreed to operate a reduced schedule to help mitigate the effects of the snow which is likely to fall throughout Thursday afternoon and early evening.
"We are refunding or rebooking any affected customers onto alternative flights so they can continue their journeys as soon as possible.
"Customers on some flights can also choose to travel on alternative dates even if their flight is still scheduled to operate."
The airline advised customers to check the BA website for the latest information.
Police said there were some minor road accidents in the Highlands while in central Scotland there was a three-vehicle crash at junction 4 on the M77, where no injuries were reported.
Although the snow is expected to cause major disruption for some, Argos has reported a 300 per cent increase on people searching to buy sledges.
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