Nature’s wonder: thundersnow

The recent nor’easter brought a surprise to many. Thundersnow.

My new home weather station sent me an alert about a lightning strike several kilometres away during the storm.

Wondering if it was true or a mistake, I quickly checked lightning detection. To my surprise, thundersnow was being reported near Prospect and Sheet Harbour.

It was only about 10 minutes later that my phone alerted my again, this time closer. I then immediately heard the thunder myself.

As someone who loves the weather, this felt like Christmas morning. I just wish I had seen the flash.

Thundersnow went on to be reported in parts of southwestern and northern Nova Scotia along with parts of New Brunswick and Prince Edward Island. Rob Lavoie was fortunate enough to capture the thundersnow on video in Halifax.

But as word spread around social media about the rare winter thunderstorms, I realized not everyone knew what thundersnow is or why it’s so uncommon.

Multiple people have asked just what is thundersnow? It’s essentially a thunderstorm with precipitation falling as snow instead of rain.

I mentioned that thundersnow is uncommon, but why is that?

Thunderstorms typically form when warm, moist air at the surface rises into colder air aloft.

This is more common for us in Atlantic Canada during the summer months with more heat and humidity at the surface. During the winter, the air is colder and more stable.

However, there can be enough of a temperature difference between cool air at the surface and colder air in the upper levels, leading to the instability needed to form a thunderstorm. Add in a trigger and thundersnow can occur.

It’s important to remember the column of air must be at or below freezing through to the surface for precipitation to fall as thundersnow.

Thundersnow can cause snowfall rates of three to five centimetres and higher.

Snow also dampens and muffles the sound of thunder, limiting the distance it can be heard to typically three to five kilometers away from the lightning strike.

While thundersnow is highly unlikely overall, you’re more likely to see or hear it in Atlantic Canada. If you witnessed it, consider yourself lucky.