The formation and dangers of black ice

Much of Atlantic Canada was treated to some early-season snowfall recently, reminding us that whether we like it or not, winter is coming.

I was fortunate where I live that the snow just coated the trees and grass, melting on contact with the road. But I knew black ice could be a problem come morning.

We often hear the term black ice during the winter season, so let’s dive into exactly what it is, how it forms and why it’s so dangerous.

Of course, black ice is somewhat of a misnomer. The ice itself isn’t black, but the ice is often thin when it freezes and is therefore transparent, making it difficult to spot.

The formation of black ice varies depending on the weather we’re experiencing.

The most common situation is when above-freezing temperatures and sunshine melts snow. If that melted snow doesn’t evaporate, it freezes when temperatures dip back below zero.

Black ice can also form if temperatures fall back below freezing after a rainfall that hasn’t fully evaporated — or in several cases recently, when wet snow melted on contact with roads but wasn’t able to evaporate before freezing.

Another culprit is one I mentioned in my

Fog 101 column — freezing fog. Supercooled water droplets can freeze onto subzero surfaces such as roads and create black ice.

Black ice can form on any roadway but is more common on bridges and overpasses where the bridge freezes before the road. Areas sheltered from sunshine can also be prime locations for black ice.

Because it’s so difficult to see, black ice is

extremely dangerous.

That’s why it’s important to know what causes black ice and to use extra caution when commuting during the winter months.

Allister Aalders is the weather specialist for the SaltWire Network, providing forecasts and analysis for Atlantic Canada. #AskAllister