• "Chaos" near Stansted as travellers forced to walk along motorway to the airport
• Britain battered with 9 inches of snow
• Could be seen as far south as London
• Major risk is now of thundersnow freezing over
• Temperatures plummet, Highways Agency warns of transport dangers
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• 300 schools closed and flights cancelled
Britons have been warned to brace themselves for perilous roads and disruption today as the “thundersnow” freezes over, bringing potentially treacherous driving conditions.
Roads ground to a halt yesterday, flights were cancelled and 300 schools were closed as Thundersnow storms battered large parts of northern Britain with up to 9in (23cm) of snow falling in some areas.
The resulting ice will pose the major danger today, forecasters warned, and some sleet and snow storms could also strike.
The Highways Agency warned of icy roads as temperatures plummet and said its gritters will be out in force.
— UBER DRIVER (@gazzeast) January 30, 2015
@STN_Airport Stansted operators at their best, no buses, walking in the road and in mud. Missed flights, thanks Stansted for all your help!— Talking Tiger (@TigerTalking) January 30, 2015
Thundersnow is quite rare. It is caused in the same way thunder and lightning are triggered during the summer, when a pocket of warm air at ground level rises and collides with the colder air above it. Even though temperatures in the UK are, in places, a little over freezing, the air above it is still significantly cooler. In the summer, this process creates heavy rain showers and lightning storms. In the cooler winter, the country is pelted with snow instead. The snow contained within the thunderstorm acts to dampen the sound of the thunder and while the thunder from a typical storm might be heard many miles away, the thunder during a thundersnow event will only be heard if a person is within two to three miles of the lightning. When thundersnow occurs at night the lightning seems brighter - this is because the lightning reflects off the snowflakes.
Travellers heading to London Stansted Airport this morning said they were forced to abandon their vehicles and walk along the M11 motorway to reach their flights, as snow blanketed the airport.
A spokesman for Stansted told The Huffington Post UK that some flights had been delayed as ice was cleared from the runways - a normal procedure during icy weather - and two flights that were scheduled to depart between 6am and 7am still hadn't left at 8.30am.
He said there had been "quite a bit of snow overnight" and conditions were "treacherous" on the nearby roads, although he wasn’t aware of people walking to the airport. Several accidents had been reported on the M11 motorway, he said.
It's very snowy at London Stansted airport this morning. Am hoping that our flight's not affected. pic.twitter.com/aKXjq4CCdB— Mums do travel (@grettaschifano) January 30, 2015
The Met Office has issued yellow "be aware" weather warnings for ice and snow across the entire country.
Helen Roberts, a forecaster at the Met Office, said: "Ice is going to be the main hazard tonight and we could see more snow".
"We could see some more sleet and snow coming in from the north west - the remnants of it could clip the south east and as far south as London.
"The chances are that by the time it reaches the south it will be less intense, but there could be a light dusting of snow over those areas."
"I will imagine there will be more transport problems with the ice potentially being more of a hazard than snow.
"The strength of the wind is making things feel extremely raw."
Holidaymakers were left stranded yesterday as Manchester Airport closed both of its runways for several hours, while flights were suspended at East Midlands Airport.
Glum-looking travellers at Manchester Airport were led back off planes carrying hand luggage while airport staff used shovels to clear the snow.
More than a dozen rail services between Manchester and Yorkshire were cancelled and main roads in Durham and Yorkshire were shut.
The disruption was so severe that Prime Minister David Cameron announced on Twitter that he has asked for updates on the weather and measures taken to keep transport systems and energy supplies running.
He said: "I have asked for an update on our heavy snow contingency plans. The gritters are out and people should listen to warnings."
Northern parts of the UK were worst hit by the snow storms. Tulloch Bridge in Inverness-shire had 9in (23cm) of snow, while there was 8in (21cm) at Glenanne in Armagh and Spadeadam in Cumbria had 5in (13cm).
A fierce Arctic blast will sweep the country on Saturday and Sunday, bringing snow across the north, and down the south west and east coasts of England and East Anglia.
Roads maintenance company BEAR Scotland said it is monitoring the situation.
Eddie Ross, BEAR Scotland's North West Operating Company Representative, said: ''The North West and North East Trunk Roads have experienced intermittent snow showers throughout the night on most routes.
"Our winter teams have worked throughout the night and the Trunk Roads in North West and North East are clear and currently have no issues.
''We will continue to monitor weather conditions and patrol and treat routes as necessary throughout this period of winter weather.
"We encourage motorists to check travel updates before setting out, prepare for their journeys and drive with care as these wintry conditions are set to continue into next week."