You can’t change the weather, but you can suppress the size of hailstones in Alberta to mitigate damage to properties, says an expert at Cat IQ Connect in Toronto.
A weather modification process called cloud seeding can limit the fertile environment for hail growth. It reduces the size of hailstorms by dispersing the water across “more small hailstones that will do exponentially less damage, with a lot less kinetic energy as they fall down,” says Adam Brainard, chief meteorologist at Weather Modification LLC.
This process was implemented during the Calgary hailstorm on Aug. 5, 2024, which caused $2.9 billion in insured damages. Is it possible the damage could’ve been worse without cloud seeding? Yes, but it’s complicated to measure, Brainard explains.
What is cloud seeding, and how does it work?
Hailstones are formed when water droplets created during thunderstorms are carried by updraft winds to levels in the atmosphere that are well above the freezing level.
When a storm’s been forecasted, meteorologists can interfere with the formation of the hailstones by using aircrafts to spray a chemical called silver iodide into the storm.
Silver iodide is an “ice nucleating particle, but it works at warmer temperatures than what ice nucleating particles would naturally be found in the environment,” says Brainard.
Specifically, these supercooled liquid water droplets start forming large hailstones at about –15 C to –20 C, says Brainard. But with silver iodide, meteorologists can start that freezing process earlier, at about –5 C, which is “much lower in the cloud” and means the hailstones won’t grow as large as they would if they were higher in the atmosphere.
“So at the end of the day, we’re taking the same amount of supercooled liquid water that used to be in the cloud, and distributing it over many, many additional ice nucleating particles,” he says.
It’s not possible to eliminate hail, but meteorologists can limit its ability to grow into larger hailstones.
This results in the creation of more but smaller hailstones, as opposed to fewer but larger hailstones, which have a higher propensity to damage when falling from higher altitudes.
Weather Modification LLC has been cloud seeding in Alberta since 1996, but it’s hard to empirically say how effective cloud seeding would be on a storm-by-storm basis.
That’s because nature is a “terrible laboratory,” says Brainard.
Cloud seeding can’t create or stop hailstorms; it just modifies existing ones, which makes it difficult to assess.
“You can’t seed a storm and then go back and repeat the experiment and not seed it and empirically say…’We had this effect,’” he says. “What you can do is you can look at a lot of seeded and non-seeded storms and try to get some confidence” about the differences of impact.
Brainard says the Institute for Catastrophic Loss Reduction (ICLR) looked at 10 years’ worth of data on cloud seeding and found about 60% of seeded storms had a measurable effect on hail size and area of impact.
“The effect was more noticeable or more distinct in larger storms,” he says.
According to ICLR, once hailstones are about the size of a quarter, they can cause extensive damage to vehicles and properties.
Brainard says southern Saskatchewan and southwestern Manitoba actually generate more severe hailstorms, with Alberta a close second.
In Canada, Weather Modification LLC does its cloud seeding in Alberta. The company concentrates its efforts in Calgary, the most populous city in the prairies, though it protects cities across the province.
Cloud seeding Canada’s costliest hailstorm
The massive hailstorm that hit Calgary on Aug. 9 and caused $2.9 billion in insured damages was a seeded storm, says Brainard.
Despite this, it still broke records as the second-costliest insured event in Canada’s history and was the most destructive event of 2024.
“We knew it was coming. We had a really good forecast. We saw it coming off the mountains,” says Brainard. “I wish we could have eliminated the hail but at the end of the day, that was a monster storm. It was oversized. It kept having cell mergers that collided into it. It was a very difficult seeding environment in that aspect.”
Rotating, long-lived, severe thunderstorms like the Calgary storm are called supercells and tend to produce the largest hail.
Brainard believes cloud seeding has an effect on all storms, but cell mergers “make things a little more difficult because they can obstruct our access to feeder fields and temporarily disrupt our aircraft.”
Damages from the storm impacted nearly one in five homes, said the Insurance Bureau of Canada (IBC). Of the 130,000 insurance claims filed, about 70,000 of them were for damage to vehicles, IBC said in the month following the storm.
“Severe storms rolled off the foothills and brought massive hail to the region,” says Laura Twidle, president and CEO of Cat IQ, during the conference. “Sidings were shredded. Cars were smashed or dented.”
The north end of Calgary saw golf ball-sized hail, while the southeast end saw baseball and tennis ball-sized stones.
The Calgary airport building and some plane fleets were damaged. Air travel was cancelled or delayed, affecting more than 10,000 travellers.
Feature image by iStock.com/juefraphoto
