Hundreds of schools in Scotland have been closed, some for a fourth day, due to heavy snow amid weather warnings across many parts of the UK. Much of Britain endured temperatures below freezing overnight on Wednesday, with preliminary data from the Met Office indicating the mercury fell to -13.6C at Tulloch Bridge in the Highlands, and as low as -11C in England. The UK had its coldest night of the winter so far on Tuesday, when the temperature fell to -14C in Dalwhinnie in the Scottish Highlands. The cold weather is expected to linger over the coming days. The Met Office put in place yellow warnings for snow and ice in most of northern Scotland, Northern Ireland and Wales and small areas of north and south-west England on Thursday and Friday. An amber warning for snow across northern Scotland, the Orkney and Shetland Islands was in place until 6pm on Thursday, with the potential for up to a further 20cm of snowfall. A yellow weather warning has also been introduced for wind, running for 24 hours from 6am on Sunday across the UK, except Shetland and south-east England. Winds of up to 70mph could hit exposed coasts, with speeds of up to 60mph inland. All schools were closed on Thursday in Orkney and in Shetland, where many have been shut since Monday. In Aberdeenshire, about 130 schools were shut and others have delayed openings, while in Moray nine schools and nurseries were closed due to the weather and others had late or staggered starts. The Met Office chief meteorologist, Jason Kelly, said on Thursday morning: “With deep snow already lying on the ground for many in the northern half of the UK, we’re going to see a significant topping up of totals over the next couple of days, especially for those in the north of Scotland. “Within the amber warning area, an additional 15-20cm of snow is possible in a few locations. “Strengthening north-westerly winds will also cause some lying snow to drift, potentially bringing some additional hazards, such as temporary blizzard conditions.” Travel warnings are also in place across Scotland. The minister for transport for Scotland, Fiona Hyslop, said: “We know from recent severe weather events that it’s important to plan ahead if you are looking to travel. “With the Met Office issuing an updated amber warning for snow in the north Highlands and Northern Isles, travel planning becomes vital. “Police Scotland is warning of a high risk of disruption for the parts of the country covered by the amber warning, but yellow warnings can also be impactful and cause delays. Please allow extra time for your journey and consider if it can be delayed until conditions have improved. “Winter resilience plans have been in full effect, with teams across Scotland working overnight to grit the trunk road network for essential journeys. “Local roads may also be impacted, so please make sure your route is available, follow the travel advice from Police Scotland and drive to the conditions.” ScotRail has halted services from Dundee to Arbroath, Montrose to Inverurie and Inverness to Elgin, while services between Inverness and Edinburgh/Glasgow will take 30 minutes longer. National Rail warned the wintry weather could affect train journeys on Thursday. The broader National Rail network is expected to be affected, with Great Northern, Thameslink, ScotRail and South Western Railway already reporting delays. In Northern Ireland, people have been urged not to travel unless it is “absolutely essential” because many roads have not been gritted, as public sector workers walk out in the biggest strike in the region’s recent history. Another frosty night is forecast into Friday, and while it will be breezier with more cloud in places, lows of -10C will again be likely in some areas. Wind coming in from the Atlantic in the west will then take charge through Friday and into Saturday, bringing much milder, wet and windy weather for the weekend. The Met Office has put in place yellow warnings for rain across most of the UK on Sunday.