London weather: Capital forecast to freeze within days as cold snap sweeps UK

London is braced for a cold snap with temperatures predicted to fall below zero overnight at the end of the week.Temperatures are expected to plummet after the capital, along with many other areas in the country, emerged from days of fog.London’s gardens and pavements could be hit by frost overnight into Thursday, with rural outskirts of the city possibly seeing temperatures as low as -3C, according to the Met Office.The UK forecaster said temperatures on Friday in London could sink to zero, while BBC Weather calculated that it could plunge to -1C.Fog shrouded the capital at the start of the week PAKathryn Chalk, an operational meteorologist at the Met Office, told The Standard: “Temperatures will be falling away over the next few nights as a colder air mass comes down from the north.“Overnight frost is expected from tomorrow night, even for the towns and cities. We could see temperatures drop as low as minus three in the countryside.”The forecast for below-zero conditions overnight comes as health chiefs issued the country’s first cold alert of the winter.The yellow cold health alert warning from the UK Health Security Agency covers England’s North West and West Midlands regions from 9am on Thursday to noon on Saturday. London is currently unaffected.Forecasters said the early frost on Thursday in London is forecast to give way to a dry, bright and largely sunny day, with a maximum temperature of 9C.It is likely to become breezy in the city, with the night once again cold and frosty. The Met Office said there will be another cold and frosty start on Friday, but that, like Thursday, it is also expected to develop into a dry day with sunshine. It is due to become cold again overnight from Friday into Saturday. The weekend is expected to be cloudier and less cold, while remaining dry, the nation’s forecaster added.Read MoreWith the temperatures sinking lower, speculation about the possibility of snowfall across the UK has been growing in recent weeks.Frost is expected to give ways to brighter days on Thursday and FridayVictoria Jones/PASome weather watchers believe the effects of El Niño – a super-sized natural climate pattern coming from the Pacific Ocean that, combined with global warming, can induce extreme weather – and a possible weakening of the polar vortex could bring about a severe cold snap.A polar vortex, a large area of strong westerly winds circulating high above the Arctic, can help contain extremely cold air around the North Pole. When it is strong, it can encourage a powerful jet stream, directing Atlantic weather systems towards the UK and bringing relatively mild, wet and windy conditions.But the polar vortex can weaken, become displaced or even split. These changes can influence the jet stream lower down in the atmosphere, potentially allowing colder Arctic or continental air to move southwards towards the UK. In some cases this can create the conditions needed for frost, ice and snowfall.