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Southern Alberta lived up to its nickname as Canada’s “hail street” this week when an intense storm dropped hail the size of softballs, shattering windows and tearing the roofs off dozens of vehicles at the QEII near Red Deer Monday.
And while large hail events are not uncommon in the province, experts warn that severe storms that produce large hail could occur more frequently due to climate change.
But how do hail get so big and why are these types of storms more likely in the future?
Supercell storms and hail
Hail can occur in many different types of storms, but they need specific conditions to grow.
Hail is formed when water droplets are lifted into the sky by updrafts associated with strong storms.
When they rise high enough, they will freeze and grow in size as they collide with more drops.
When they are large and heavy enough that the storm’s updrafts cannot support them, they will fall. The longer the hail stays in that cold part of the storm cloud, the bigger it will grow.
Jesse Wagar, a meteorologist with Environment and Climate Change Canada, says that for these very large hailstones you need more than your typical storm.
“These storms that produced this significantly large hail, they are supercell storms, which are necessary to get the hail to reach the sizes that they did,” says Wagar.
Supercell storms have what is called a mesocyclone inside the storm cloud.
Supercell storms have strong updrafts that help create larger hail. (Kelly delay)
It is a powerful rotating updraft that allows hailstones to last longer and become larger.
Wagar says that in addition to the power of the storm, things like moisture in the lower and middle levels of the atmosphere and freezing levels, or how high you have to go for temperatures to approach freezing, are also important elements.
Wagar says that once the hail starts falling and moves to the bottom of the cloud, it will begin to melt.
“The bigger the rock, the less likely it is to melt once it gets lower in the atmosphere.”
Why is Alberta a hot spot for hail?
Alberta’s geography makes it a prime location for hail to form and fall.
“To get supercells, you need a certain wind regime to spin those storms, which the mountains will help do,” says Wagar.
“We’re in a gravel alley along the foothills.”
Higher foothill elevations will mean a shorter distance for hail to fall below that freezing level, which can reduce melting on smaller rocks.
This time of year can also create the perfect storm with plenty of heat and humidity to create enough energy to support these storms.
Wagar says mature crops can also help pump moisture into the lower atmosphere through transpiration and evaporation.
He says all of these elements come together to provide the perfect environment for these dangerous very large hail storms.
A hailstorm in Calgary in 2020 with hail the size of a light and a ton ended up being one of the costliest natural disasters in Canadian history, damaging at least 70,000 homes and vehicles and destroying entire crops. The damage bill was put at about $1.2 billion.
A hailstorm in Calgary on June 14, 2020 caused nearly $1.2 billion in insured damage. (Jeff McIntosh/The Canadian Press)
Where does climate change fit in?
As with many types of weather phenomena, climate change is affecting the formation of hail.
Julian Brimelow is the executive director of the Northern Hail Project at Western University. He has studied the cases of hail and how it has evolved in North America.
“There are indications from around the world that in certain areas the frequency of larger hail is increasing, although perhaps the number of hail days is decreasing,” he said.
“Our modeling research suggests that, over hail alley, the number of large hail events and the average hail size during hail events could increase in the future.”
Brimelow says there are a number of reasons for these changes.
First with a warmer atmosphere, smaller hail could melt before it hits the ground. This means perhaps fewer days with hail events over the course of a year.
“What’s not so intuitive is that we’re going to have more very large hail events, and that’s because these large hailstones are falling so quickly,” he says.
“So there’s very little time for them to experience fusion, you know, because they’re falling at over 100 kilometers per hour.”
Large hail picked up northwest of Markerville, Alta., Monday. (Northern Hail Project)
Another factor has to do with the humidity levels in our warm atmosphere.
Warmer air can hold more moisture than cooler air, Brimelow says. So with our hotter summers and more moisture available at lower levels of the atmosphere, that means there could be more fuel for these storms to produce large hail.
“It favors the strong updrafts of summer storms that grow these large hailstones because you have to keep the particles or hail suspended in the updraft long enough for it to grow.”
Brimelow says that this change in the frequency of hail events has been documented through his studies, but reliable observations have historically been difficult to come by.
He says weather models provide a clearer connection, and his research is a starting point for more as the technology continues to advance.
“Computationally [modelling thunderstorms] it is very expensive and takes a long time. But we anticipate that as computational power increases going forward, we will be able to do that.”
Our planet is changing. Our journalism too. This story is part of a CBC News initiative called “Our Changing Planet” to show and explain the effects of climate change. Stay up to date with the latest news on our Climate and Environment page.