A decision support tool for dry persistent deep slab avalanches for the transitional snow climate of western Canada

A decision support tool to aid in forecasting the likelihood of dry persistent deep slab avalanches was created from three separate data sources in western Canada. Data were obtained from an expert opinion survey of avalanche professionals, a dataset of avalanched starting zones that were field-investigated, and a dataset of avalanches from the Canadian information sharing system. The survey and the tool consisted of three sections: snowpack conditions, weather conditions, and avalanche observations. Parameters in the tool were assigned importance values derived from the survey responses. A classification tree was used to determine the threshold tool sum for increasing the likelihood of observing natural persistent deep slab avalanches. Based on some of the data used to create the tool, the tool correctly explained 75% of days with natural avalanches (16 out of 18) and non-avalanche days (61 out of 85), but the false alarm ratio was high (60%). The tool also indicates if triggered avalanches from localized dynamic loads are possible, depending on responses in the snowpack conditions section of the tool. Avalanche forecasters must apply the tool to certain terrain characteristics, at a local to regional scale. The tool may benefit from location-based calibration. The tool only indicates the likelihood of persistent deep slab avalanches based on the datasets used and it cannot determine when or where they will occur.