Three years of monitoring severe hailswaths across Canada using radar

One of the primary goals of the Northern Hail Project (NHP) is to generate the first detailed hail climatology for Canada. To do this, we are adopting several independent approaches. One of these is the use of the Maximum Expected Size of Hail (MESH) from radar data. Most of the 33 new S-band dual-polarization radars have been operational since early 2022. Using these radar data allowed us to identify hailstorms at high-spatial temporal resolution wherever we have radar data. In this research, we focused on manually identifying (and digitizing) severe hailswaths using the MESH data from 2022 through 2024.  A severe MESH hailswath is one that has a continuous 40 km long or greater track of 10 mm pixels, and must include at least 2 adjacent pixels of 30 mm or greater. A total of almost 2,000 severe hailswaths have been identified by radar to date. Although the regional year-to-year variability is significant, our analysis has identified the Canadian Prairies and far western Ontario as hot spots for long-lived, severe hailstorms. Some of the severe hailswaths in the dataset are impressive, extending over 500 km and lasting up to 6 hours. The widest hailswath in our MESH dataset is approximately 50 km across. Even though most of the MESH hailswaths in our database have occurred near or just to the north of the Canadian/U.S border, some hailswaths have occurred at the edge of our available radar network range, with the most northern MESH hailswath terminating at a latitude of 58.0 degrees north in Saskatchewan. Moving forward, we will continue to monitor severe hailswaths using a semi-automated algorithm that draws on machine vision and machine learning techniques and will be trained on the existing dataset. In 2022, we used the MESH product produced by the National Oceanic and Atmospheric Administration-Multi-Radar Multi-Sensor (NOAA-MRMS) and switched to the Environment and Climate Change Canada (ECCC) MESH product in 2023 and 2024. Although the products from the two groups are generally in good agreement, we noted that there are notable differences in the MESH values at times. Reasons for these discrepancies are being investigated using ground reference data collected by the NHP.