Atmospheric Conditions and Precipitation Types Observed during the April 2023 Ice Storm over Montreal, Quebec, Canada

On 5-6 April 2023 a high-impact storm produced freezing rain and ice pellets over southern Quebec, Canada. Freezing precipitation led to major power outages, transportation delays, and two fatalities. More than 800 trees were damaged in Montreal alone, causing some areas of the city to be without power for up to five days. The goal of this study is to investigate the atmospheric conditions leading to freezing precipitation during this high-impact storm. To do so, we used field observations and measurements, as well as reanalysis products. Observations were conducted simultaneously in downtown Montreal and in Morin Heights, a town approximately 100 km north of Montreal in the Laurentian Mountains. In Montreal, an accumulation of 30 mm of precipitation with 12 mm of ice accretion were measured during a precipitation event that lasted around 12 h. In contrast, up to 10 cm of ice pellets with only 8 mm of ice accretion were reported in Morin-Heights over a duration of around 24 h. Precipitation rates peaked at approximately 18 mm/h at both locations. In Montreal, the accumulated ice on infrastructure and trees melted 12 h after the end of precipitation when the temperature increased above 0°C. The impacts of this storm were mitigated by the occurrence of ice pellets for some areas, and by the warm temperatures that followed the event. For this region, this storm represents the most impactful freezing rain event since the catastrophic 1998 Ice Storm.