What Are Snow Squalls and Why Are They So Dangerous?

People bundled up for the cold walk on the sidewalk during snowy weather.
These people in Canada wouldn’t be walking so calmly if a snow squall was happening in this photo.
Lars Hagberg/Getty Images

As much of the Midwest buckles under bitter sub-zero temperatures and Chicago has had to literally set fire to railways to keep the trains running, residents of much of the East Coast now have to contend with another wintry weather phenomenon: the snow squall.

This isn’t the same thing as a snow storm. As the National Weather Service explains, a snow squall takes the form of an intense but brief hammering of snow and winds. They can come in waves, but they generally only last somewhere between 30 minutes and an hour before they pass.

But that brevity can also make snow squalls more dangerous.

They happen quickly, without all the warning of a coming snow storm—something that can last for hours or days—and they can catch people by surprise. Roads can become quickly slick, and white-out conditions can make it impossible to see, often resulting in pile-ups and road closures.

On Wednesday, as many as 40 cars slammed into each other in a crash from a snow squall in Pennsylvania, leaving at least 25 people injured. It was reportedly one of many squall-related wrecks in the northeast. Experts are warning that they could make the evening commute in Boston treacherous.