Calgary hail season explained

Hail forms inside thunderstorm clouds. Strong updrafts, which are rising currents of air, carry raindrops high into the cloud where it's well below freezing. The drops freeze, pick up more supercooled water, and grow in layers until they're too heavy for the updraft to hold. Then they fall. Environment and Climate Change Canada says hail can reach the ground at speeds of up to 100 km/h or more.

Alberta's geography is close to ideal for that process. The Insurance Bureau of Canada (IBC) describes it simply: mountains and elevation create moist air near the ground with very cold, dry air above it. On summer afternoons the sun heats the land, warm moist air rises along the foothills, and storms can grow tall enough to reach the cold air aloft. The Canadian Encyclopedia notes that while hail happens in every province, it's most frequent and severe in Alberta and Saskatchewan.

Hail can fall in any warm month, but the damaging storms cluster in summer. The insurer-funded Alberta Hail Suppression Project was set up to run through the summer storm season, with operations continuing to September 15. Intact Financial Corporation describes July as typically the most active month for hail, and the Canadian Encyclopedia notes that in central Alberta the most severe storms come in July and August, mostly from late-afternoon or evening thunderstorms.

That timing lines up with Calgary's recent history. The big insured-loss storms of the last several years landed on June 13, July 2, July 13 and August 5.

Warnings and news reports describe hail by comparing it to everyday objects. The sizes below come from the U.S. National Weather Service's standard descriptor chart, converted to centimetres. The right-hand column is a general guide from the roofing side, not a rule. Wind, the age of the roof and the angle of impact all change the outcome.

Insured losses are published by IBC using estimates from Catastrophe Indices and Quantification Inc. (CatIQ). They cover insured damage only, not uninsured losses. They also get revised, often sharply. The July 2021 storm was first estimated at $247 million and later passed $600 million.

The Calgary storm archive keeps these figures with their sources and the date each estimate was published. Use it when you need to pin down a date of loss.

IBC reports that Alberta has had at least one major hailstorm every year for two decades, with more than $11 billion in insured damage over that time and $6 billion in the last five years alone. Across Canada, IBC puts insured losses from catastrophic weather events and wildfires at $37 billion from 2016 to 2025, compared with $14 billion over the previous decade, adjusted for inflation.

Some of that is exposure. A storm crossing a bigger city hits more roofs, more siding and more cars than the same storm would have a generation ago, and every one of those costs more to repair. IBC has called for Calgary to adapt to "our new weather reality", including requiring hail-resistant roofing and siding on new construction in high-risk areas.

For you, the practical result can show up in your policy, for example as a separate or higher hail deductible, or different terms for the roof. Check your declarations page at each renewal and ask your broker to explain any change. Percentage deductibles in Alberta explains how to read a hail deductible.