Councils are preparing to kickstart extreme weather plans as forecasters warn of plummeting temperatures and up to 10cm of snow.
The Met Office said elevated areas could see snow piles on Wednesday morning, with the white stuff expected to fall over vast areas of the UK.
Warnings are in place across the south of England, the Midlands and the north, as well as Wales, and central and western parts of Scotland.
Snow flurries could begin as early as 9pm and continue into the early hours, combining with freezing temperatures to bring the threat of frost and ice.
Grahame Madge, of the Met Office, told HuffPost UK: “As the front moves through Tuesday night into early Wednesday it will bring snow to a large area.
“We’re looking at 1cm to 3cm but up to 10 in exceptional circumstances and in areas with high ground.
“There will be behind it much colder air and clear skies and will cool things down further, bringing with it widespread frost and ice.”
Officials said the forecast meant an array of challenges for keeping roads open.
A spokesman for Glasgow Council said 900km of carriageways in the city would be cleared as a priority should snow and ice fall overnight.
The roads cleared would include key bus routes and streets near hospitals and police stations.
The authority will use 500 tonnes of salt over the next day, but raised concerns that heavy rain and sleet could wash it away.
“We’re seeing a real mixed message in terms of snow, sleet and ice,” the spokesman said.
“One concern is that once grit is out on roads, it can be washed away by rainfall later. It will be challenging over the next 24 hours that’s for certain.”
Glasgow has a night shelter programme in place for rough sleepers throughout winter, but the council said it would be seeking to promote this as temperatures plummet further.
The shelter, which is run by a charity partner, has 40 beds.
In England, Wiltshire Council said it had plenty of salt stocks ready to go in the event of snow and ice.
The council has also implemented its severe weather emergency provisions to ensure homeless people can access overnight accommodation and support.
The situation was similar at other authorities contacted by HuffPost UK including Manchester City Council, Central Bedfordshire, Cardiff and Hampshire.
Meanwhile travellers were told to brace for disruption.
The AA said motorists should prepare before setting off and carry blankets, food, water and a torch, in case they become stuck in tailbacks.
Network Rail said passengers should brace for slow-moving services if snow falls and ice develops.
The infrastructure provider said it would activate special sections of heated rails to ward off ice on busy routes and train companies would be operating empty services to keep tracks clear.
Andy Thomas, managing director of strategic operations at Network Rail, said impact to passenger services will be “minimised” but conceded that trains may be forced to slow down.
“When conditions are very serious, trains might have to slow down – just as a car would on a road – this is so everyone can get where they need to go, safely,” he said.
Meanwhile, Britain’s busiest airport, Heathrow, advised passengers travelling on Tuesday evening and Wednesday to check with their airline before setting off.
A Heathrow spokesperson said: “To ensure our passengers and colleagues are traveling safely this winter, Heathrow is closely monitoring and preparing for cold weather conditions forecast for the UK.
“Those traveling via Heathrow are encouraged to contact their airline for up to date flight information.”
RAC Breakdown spokesperson Rod Dennis said: “Drivers face some treacherous conditions as some truly wintry weather finally descends on large parts of the UK.
“Rain will quickly turn to sleet and snow through Tuesday afternoon, making driving conditions challenging. We strongly recommend drivers reduce their speed and more than double the amount of space between themselves and the vehicle in front, giving them more time to react if they need to.
“But the bigger problem for most drivers is likely to be the threat of ice overnight on Tuesday and into Wednesday morning’s commute. Roads and pavements will freeze overnight, leaving glass-like surfaces that will increase the risk of drivers, cyclists and pedestrians running into difficulties.
“Before setting out, it is vital that motorists check their car is up to the task of coping with the more wintry conditions – many breakdowns are preventable with the right preparation. Spending a few minutes checking over tyres, together with oil, coolant and screenwash levels could save hours stuck at the side of the road in the cold.
“Nonetheless, our patrols and the teams supporting them behind the scenes will be working exceptionally hard to assist all those people whose cars fail them.”
