Why is brown snow falling in the US Midwest?

After a major winter storm hit parts of the US this week, residents of Minnesota have noticed something unusual about the fresh snowfall.

Rather than blanketing the state in bright white powder, the snow was marbled with patches of brown and orange.

But what is causing the so called "dirty snow"?

Chris O'Brien, a meteorologist at the US National Weather Service, told Time magazine that the discoloration is caused by dust particles carried on strong winds all the way from Texas.

"[The wind] picked up a lot of dust and got it entrained into the circulation of this storm system and pulled it all the way up into Minnesota where it fell with the precipitation," he said.

Satellite images show large plumes of dust drifting northwards from the US-Mexico border.

While dust mixing with snow has happened before, Mr O'Brien says it's unusual for it to travel such distances.

"We get the discoloured snow sometimes, but usually it's from dust that's closer to here, not … from all the way close to the Mexican border," he said.

• 'Orange snow' baffles eastern Europeans

Some on social media christened the off-white snow "snirt" - a portmanteau of snow and dirt.