Millions affected by US winter storm causing power cuts and school closures

A winter storm is spreading across the United States, causing schools to close, roads to shut and travel plans to be disrupted in many areas.

The storm stretches from Texas in the south to New England in the north-east and is affecting a huge part of the country.

Weather experts say around 180 million Americans – more than half the population of the US – could feel the effects of the storm. Nearly half of all US states have declared emergencies.

Many places are seeing heavy snow, sleet and freezing rain all at once. Freezing rain is especially dangerous because it turns into ice as soon as it touches the ground. This makes roads, pavements and bridges extremely slippery and can cause trees and power lines to become coated in ice.

When ice builds up on power lines, they can snap or fall, cutting off electricity, and more than 800,000 households across the states have lost power. Officials are asking people to stay indoors where possible and check on neighbours who may need help.

Travel has also been badly affected. More than 11,000 flights have been cancelled because planes cannot safely take off or land in snowy or icy conditions.

Many schools have cancelled classes and announced they’re closed in anticipation of the storm continuing on Monday - as buses and cars cannot travel safely on frozen roads.

In Washington DC, Mayor Muriel Bowser described how serious the situation is, saying: "We're experiencing the biggest snowstorm in a decade in DC this weekend." The US Senate has even postponed a planned vote because of the weather.

While places in the north such as the Dakotas and Minnesota are used to below-freezing temperatures in winter, it is unusual to see such extreme cold in states like Texas, Louisiana and Tennessee, where temperatures are around 15-20C below the seasonal average.

The storm is being caused by something called the polar vortex. This is a huge ring of strong winds that circles the Arctic every winter and holds very cold air in place. Sometimes the winds weaken, allowing cold air to move south into the US. When this icy air meets warmer air, storms can form.

Meteorologist Allison Santorelli from the National Weather Service explained why the problems may last, saying: "The snow and the ice will be very, very slow to melt and won't be going away anytime soon."

The storm is expected to move east over the next few days, but very cold weather could continue into early February. Authorities are reminding families to follow local advice, stay warm, and put safety first until conditions improve.