Diagnosing tornadic environments in the western coasts of North and South America

The western coasts of Chile and the U.S. have similar geographies and climate. They both occasionally feature environments with high wind shear and low instability that favor the development of severe storms and tornadoes, particularly in the fall and winter months. Previous work found that the mixed-layer CAPE, the storm-relative helicity between 0-500 m, and the effective bulk shear were skillful in diagnosing the seasonality of tornadic environments in central-south Chile. We evaluated a new composite parameter based on these variables that has shown superior skill representing the high-shear and low-instability environments of tornadoes in south-central Chile between 1980 and 2023 and along the U.S. west coast over the same period. In addition, the new parameter scales with tornado intensity, with larger values found for more intense tornadoes. Our results suggest that this new parameter can be applied in a forecast setting to characterize tornadic environments along the west coasts of North and South America.