The $3.25 billion Calgary, Alberta Hailstorm: a Meteorological Case Study and In-Situ Observations from the Northern Hail Project

A destructive hailstorm hit Calgary, Alberta, Canada on August 5th, 2024, resulting in $3.25 billion CAD of insured losses – this made it the second costliest natural hazard event in Canadian history, in terms of insured losses. The storm caused widespread damage to the northern areas of the city. We will present results on the storm’s evolution, meteorological environment, and behaviour, to better understand the mechanisms behind its intensity and to inform the forecasting and mitigation of future hailstorms. On this day, the Northern Hail Project (NHP) field teams also collected in-situ data along the storm’s track; the largest hailstone that was found measured 52 mm in diameter. Hail was recorded at four NHP hail-monitoring stations located in the affected areas of the city. Colleagues from the Insurance Institute for Business & Home Safety (IBHS) also captured high-resolution data from an array of hail disdrometers deployed ahead of the storm. 

Synoptic conditions on the day were broadly supportive for the development of severe thunderstorms, although the environment did not suggest conditions were in place to support an exceptionally damaging hailstorm. Examination of ERA5 reanalysis data revealed a favourable kinematic profile, characterized by 20 m/s of 0-6 km bulk wind shear, as well as surface-based CAPE near 1,200 J/kg and 19 mm of precipitable water. The storm initiated over a zone of enhanced surface convergence and upslope flow along the front range of the Rocky Mountains northwest of Calgary. Once away from the terrain, the storm rapidly intensified and began producing large quantities of damaging hail. Just prior to entering the city limits, the storm became outflow dominant, producing measured wind gusts up to 65 km/h. These winds significantly increased the level of hail damage. The storm continued to produce severe hail after leaving the city.  

Ultimately, it was the combination of an outflow-driven storm, over an urban area, which produced such extensive damage. Therefore, insights gained from this investigation, particularly the detailed in-situ observations and environmental analysis by the NHP, underscore the importance of high-resolution monitoring to advance hailstorm forecasting and impact mitigation.