Unusual weather phenomenon observed during Ontario snowstorm explained

As a major snowstorm brought heavy snow to southern Ontario Friday evening, residents were met with another, surprising, weather phenomenon.

Just before 9 p.m. on Friday, residents began to report thunder and lightning amid the snowfall.

‘Thundersnow,’ simply put, is when lightning and thunder accompany a snowstorm, and although it doesn’t happen often, CP24 meteorologist Chris Potter said it’s not completely uncommon.

“Obviously, it doesn't happen frequently with each and every storm," Potter said. "There have to be certain mechanisms at play. One of them is significant lift [and] significant convection."

Residents soon began to upload photos and videos of the phenomenon.

Lightning could be seen brightening the skies as snow poured down over the city.

The phenomenon was also experienced in Kitchener, Ont., and as far as Michigan, U.S.

According to the Farmer's Almanac, thunderstorms occur when an air mass becomes so unstable that it overturns violently, usually when drastically different temperatures meet. Thundersnows are fairly rare because, in winter, "the lower layers of air are colder — and have a lower dew point, [meaning] these kinds of atmospheric clashes are very unusual during colder months."

"Still, thundersnow does happen," the organization says.

Thundersnows are most common in the Great Lakes region because cold air blowing across the relatively mild water of the Great Lakes forces the air upwards rapidly enough that the instability causes lightning and thunder in conjunction with heavy snow, according to the Almanac.

CTV News Toronto weather specialist Jessica Smith also said these types of late winter storm aren’t uncommon.

“We are entering the time of year where the battle between cold arctic air is battling against the warmer southern air as we transition into spring,” Smith said. “Texas Lows are high-impact systems.”

Smith says the storm’s greatest impact will be seen from 9 p.m. Friday through to 12 a.m. Saturday, with heavy wet snow expected through to Saturday morning.