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Southern Alberta lived up to its moniker of Canada’s “Hail Alley” this week when an intense thunderstorm dropped softball-sized hail, shattered windows and gutted the roofs of dozens of QEII vehicles near Red Deer on Monday.
And while large hail is not uncommon in the province, experts warn that strong storms causing large hail may occur more frequently due to climate change.
But how does hail get so big, and why are these kinds of storms more likely in the future?
Supercell thunderstorms and hail
Hail can occur in many different types of thunderstorms, but they need specific conditions to grow.
Hail is formed when water droplets are lifted high into the sky by updrafts associated with severe thunderstorms.
When lifted high enough, they will freeze and grow in size as they collide with more droplets.
When they become large and heavy enough that the updraft of the thunderstorm cannot support it, they will fall. The longer the hail remains in this cold part of the thundercloud, the larger it will become.
Jesse Wagar, a meteorologist with Environment and Climate Change Canada, says that for these very large hailstones, you need more than a typical thunderstorm.
“These storms that produced this significantly large hail, these are supercell thunderstorms, which are necessary for the hail to reach the sizes that they did,” Wagar says.
Supercell thunderstorms have what is called a mesocyclone within the thunderstorm cloud.
Supercell thunderstorms have strong updrafts that help create larger hail. (Kelly Delay)
This is a powerful rotating updraft that allows the hailstones to stay in the air longer and grow larger.
Wagar says that in addition to the strength of the thunderstorm, 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 reach 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 headache for hail?
Alberta’s geography makes it an ideal place for hail to form and fall.
“To get supercells, you need a certain wind regime to make these storms spin, which the mountains will help do,” says Wagar.
“We’re in an alley with hail at the foot.”
Higher foothill elevations will mean a shorter distance for hail to fall below that freezing level, which can reduce melting of smaller rocks.
This time of year can also create the perfect storm with plenty of heat and moisture to create enough energy to sustain these storms.
Wagar says mature crops can also help pump moisture into the lower atmosphere through transpiration and evaporation.
She says all of these elements come together to provide the perfect environment for these very dangerous very large hail storms.
A hailstorm in Calgary in 2020 with hail the size of moons and tuns became 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 pegged at around $1.2 billion.
A hail storm in Calgary on June 14, 2020 caused almost $1.2 billion in insured losses. (Jeff McIntosh/The Canadian Press)
Where does climate change fit in?
As with many types of weather phenomena, climate change affects the formation of hail.
Julian Brimelow is the Executive Director of the Northern Hail Project at Western University. He studied the occurrence of hail and how it developed in North America.
“There are indications from around the world that in certain areas the frequency of larger hail events is increasing, although perhaps the number of hail days is decreasing,” he said.
“Our modeling study suggests that above the hail alley, the number of large hail and the average hail size during a hail event may increase in the future.”
Brimelow says there are a number of reasons for these changes.
First, with a warmer atmosphere, smaller hail can melt before hitting the ground. This means perhaps fewer hail days throughout the year.
“What’s not so intuitive is that we’re going to have more very large hail events, and that’s because these large hail are falling so quickly,” he says.
“So there’s very little time for them to experience melting, you know, because they’re falling at over 100 kilometers per hour.”
Large hail gathered northwest of Markerville, Alta., on Monday. (Northern Hail Project)
Another factor has to do with moisture levels in our warming atmosphere.
Brimelow says warmer air can hold more moisture than cooler air. So with our hotter summers and more moisture available in the lower atmosphere, that means there can be more fuel for those thunderstorms that produce large hail.
“It feeds the strong updrafts in summer storms that grow these large hailstones because you have to keep the particles or the hailstone in the updraft long enough for it to grow.”
Brimelow says that through his studies, this change in hail frequency has been documented, but reliable observations have historically been difficult to find.
He says weather patterns provide a clearer link and that his research is the starting point for more as the technology continues to advance.
“Calculating [modelling thunderstorms] is very expensive and time consuming. But we anticipate that as computing power increases going forward, we will be able to do this.”
Our planet is changing. So is our journalism. This story is part of a CBC News initiative called Our Changing Planet to show and explain the effects of climate change. Keep up with the latest news on our Climate and Environment page.
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