Climate change means Alberta could see more large hail events in the future. Here's why

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Southern Alberta lived up to its nickname of Canada's "hail alley" this week when an intense thunderstorm brought down hail the size of softballs, shattering windows and denting roofs of dozens of vehicles on the QEII near Red Deer Monday.

And while large hail events are not uncommon in the province, experts warn that severe storms producing large hail could happen more frequently because of climate change.

But how does hail get so big, and why are these sorts of storms more likely in the future?

Supercell thunderstorms and hailstones

Hail can happen in many different types of thunderstorms, but they need specific conditions to grow.

Hail is formed when water droplets are lifted high in the sky by updrafts associated with strong thunderstorms. 

When they are lifted high enough they will freeze, and grow in size as they collide with more droplets. 

When they get large and heavy enough that the thunderstorm's updrafts can't support it, they will fall. The longer the hail remains in that cold part of the thunderstorm cloud, the larger they will grow.

Jesse Wagar, a meteorologist with Environment and Climate Change Canada, says that for these very large hailstones you need more than just your typical thunderstorm. 

"These storms that produced this significantly large hail, those are supercell thunderstorms, which are required in order to get hail to to reach the sizes that they did," says Wagar.

Supercell thunderstorms have what is called a mesocyclone within the thunderstorm cloud. 

It's a powerful rotating updraft that allows hailstones to remain aloft longer and get larger. 

Wagar says besides the power of the thunderstorm, things like moisture at lower- and mid-levels of the atmosphere and freezing levels, or how high you have to go for temperatures to approach zero, are all important elements as well. 

Wagar says that once the hailstone starts fall and passes into the lower part of the cloud, it will start to melt.

"The bigger the stone, the less likely it is to melt once it comes lower in the atmosphere."

Why is Alberta a bull's-eye for hail?

Alberta's geography makes it a prime location for hail to form and fall. 

"In order to get supercells, you need a certain wind regime to get those storms to spin, which the mountains will help do," says Wagar.

"We are in hail alley along the foothills."

Higher elevations of the foothills will mean a shorter distance for hail to fall below that freezing level, which can reduce melting on smaller stones. 

This time of year can also create the perfect storm with plenty of heat and moisture to create enough energy to support these storms. 

Wagar says mature crops can also help pump moisture into the lower part of the atmosphere through transpiration and evaporation.

She says that all of these elements come together to provide the perfect environment for these very dangerous storms with very large hail. 

A hailstorm in Calgary in 2020 with loonie- and toonie-sized hail ended up being one of the costliest natural disasters in Canadian history damaging at least 70,000 homes and vehicles, and destroyed entire crops. The damage bill was pegged at around $1.2 billion.

Where does climate change fit in?

As with many types of weather phenomena, climate change is affecting hail formation. 

Julian Brimelow is the executive director of the Northern Hail Project out of Western University. He has studied hail occurrences and how it has evolved across North America. 

"There are indications from around the globe that in certain areas the frequency of larger hail is increasing, even though perhaps the number of hail days are decreasing," he said.

"Our modelling research suggests that, over hail alley, the number of large hail events and the average size of hail during hail events could increase in the future."

Brimelow says there are a number of reasons for these shifts. 

First with a warmer atmosphere, smaller hail could melt away before it hits the ground. That means perhaps fewer days with hail events over the course of a year. 

"What isn't so intuitive is that we're going to get more events with very large hail, and that's because those large hailstones are falling so fast," he says. 

"So there's very little time for them to experience melting, you know, because they're falling at well over 100 kilometres an hour." 

Another factor has to do with moisture levels in our warming atmosphere. 

Brimelow says that warmer air can hold more moisture than cooler air. So with our hotter summers and more moisture available at lower levels of the atmosphere, that means there could be more fuel for these thunderstorms that produce large hail. 

"It powers the strong updrafts in summer storms that grow these large hailstones because you do need to keep the particles or the hail suspended in the updraft long enough for it to grow."

Brimelow says through his studies, this change in frequency of hail events has been documented, but reliable observations have historically been hard to come by. 

He says that weather models provide a clearer connection, and that his research is a jumping-off point for more as technology continues to advance. 

"Computationally [modelling thunderstorms] is very expensive and takes a long time. But we foresee that as computational power increases moving forward, that we are going to be able to do that."

Our planet is changing. So is our journalism. This story is part of a CBC News initiative entitled "Our Changing Planet" to show and explain the effects of climate change. Keep up with the latest news on our Climate and Environment page.