LONDON — A Siberian weather system making its way across Europe hit the British Isles particularly hard on Thursday, bringing heavy snow, high winds and below-freezing temperatures to areas ill equipped to handle them.

The Met Office, Britain’s national weather service, issued rare “red warnings,” meaning there is “risk to life” for Thursday and Friday, highlighting blizzard conditions in a band across southwest England and southeast Wales, including the cities of Cardiff and Exeter, and it urged people there to remain at home.

Compounding the weather problems, National Grid, the country’s main energy distributor, warned of a natural gas shortage because of high demand for heating, mechanical problems caused by the cold, and the partial closing last year of an offshore facility that accounted for most of the country’s gas storage capacity.

Officials said they were working with commercial-energy consumers to cut gas use, so that supplies for residential heating and electricity generation would not be affected.

Forecasters said that more than a foot of snow would fall in some places from Thursday afternoon through Friday morning. That will give way to freezing rain in places, coating roads and sidewalks with ice and making conditions even more dangerous for travel.

A red warning for central Scotland was lifted on Thursday, and much of Britain remained under the less severe but still serious amber and yellow warnings.

On Thursday, the third consecutive day of snowfall, most schools across Britain and Ireland were closed, as were many businesses, and even in London, which was not hit as hard as areas to the west, many normally packed streets were quiet. The week’s snowfall totals are expected to be the heaviest in decades.

Transportation networks were badly snarled by the weather, with extensive breakdowns and cancellations on subway and train services, flight delays and cancellations, and highway traffic moving at a small fraction of its usual speed. Hundreds of drivers were stranded.

Europe’s weather usually approaches from the Atlantic, to the west, keeping conditions mostly temperate, but that pattern has temporarily reversed, bringing a frigid system from Asia that meteorologists have called “the beast from the east.” Rome had its first snowfall in six years this week.

Heavy snow is unusual in southern Britain and Ireland, where the local authorities do not have the snowplows and salt spreaders that are standard equipment where harsh winters are commonplace.