An Investigation of the Canadian Prairie Supercell Thunderstorms Characteristics

Although supercell thunderstorms are infamous for producing strong tornadoes, large hail, damaging winds, and flash flooding, they trigger much of the summertime rainfall over the Canadian Prairies from June to August and determine the productivity of prairie agriculture. The frequency and types of supercell thunderstorms show an erratic pattern in recent years, but scientists are yet to understand the cause. Despite supercells' significant impacts on prairie provinces' economy, which environmental conditions are favorable for developing and maintaining supercell thunderstorms remains poorly understood. Therefore, this study uses sounding-derived severe weather parameters to explore the thermodynamic and dynamic characteristics of three types of supercell thunderstorms: low-precipitation (LP), high-precipitation (HP), and classic supercells. This study subjectively identified different supercell thunderstorm case studies based on professional storm chaser photographs. Since the Canadian Prairies lack a sufficient radiosonde observation network, the current study used radiosonde observation and proxy soundings from the Global Forecast System (GFS) model. We investigated the environmental conditions of 108 supercell thunderstorms of three types of supercells (LP, HP, and Classic) which occurred from 1999 to 2023 over the three prairie provinces: Manitoba, Saskatchewan, and Alberta, and compared their dynamical and thermodynamical characteristics with their U.S. Great Plains counterparts. Our study found that the environmental conditions of Alberta and Saskatchewan favor the development of LP supercell. The Classic supercell develops predominantly over South Saskatchewan and South-Western Manitoba, whereas most HP supercells occur over Alberta and Manitoba. We observed the following environmental control over different types of supercells: dryline control LP supercell; elevated mixed layer (ELM) originated from the Rocky mountain triggers Classic supercell; convective available potential energy (CAPE) and normalized difference vegetation index (NDVI) influences HP supercell development. Most of the tornado-producing supercells were classic types. The LP supercell over the Canadian Prairies shows more sensitivity to low-level wind shear and mid-level (700-500 mb) temperature lapse rate than their U.S. Great Plains counterparts. HP supercells over the Canadian Prairies usually develop in an environment with relatively lower convective available potential energy (CAPE) than their U.S. Great Plains counterparts. We found that the downdraft CAPE (DCAPE) and low-level (surface to 1 km) bulk wind shear and storm relative helicity show sensitivity to the types of supercells investigated. Overall, Supercell thunderstorms over the Canadian Prairies develop in an environment with lower value of CAPE, higher value of downdraft CAPE (DCAPE), lower temperature lapse rate, and smaller Bulk Richardson Number (BRN) compared to the U.S. Great Plains supercells. This study's findings will improve our understanding of the characteristics of different supercell thunderstorms over the Canadian Prairies and help operational weather forecasters prepare for improved severe weather forecasting, saving lives and properties.