Assessment of Tornado Alerting Performance for Canada

Abstract

The Northern Tornadoes Project (NTP) completed a first independent assessment of national tornado warning alerting (watches and warnings) in Canada covering the 2019–2021 period. The NTP undertook this study in the spirit of open data, understanding tornado warning issues unique to this country, and improving tornado warning performance. Utilizing the NTP tornado event database for verification, tornado alerts were reviewed for accuracy and timeliness. For the 250 tornadoes that occurred during the study period – and using a definition of what constitutes a warning ‘hit’ developed for the study – the standard 2 × 2 contingency table scores were Probability of Detection = 0.23, FAR = 0.78, and CSI = 0.13. Over 70% of tornadoes had no tornado warning, including 35 EF2 tornadoes. The tornado warning results were compared with US National Weather Service tornado warning scores for the US and US states along the southern Canadian border to provide context. NTP also developed a ‘report card’ aimed at public and media consumption that took into consideration Environment and Climate Change Canada’s national performance targets for tornado warning Probability of Detection (POD) and lead time as well as tornado watch issuance. Using weighted scores for these criteria, NTP assigned a total score of 33.3/100, indicating significant room for improvement. A follow-up assessment was conducted for the 2022 tornado season in Canada following the same established procedures. It was found that the number of both tornado watches and tornado warnings had roughly doubled, resulting in a significant increase in the POD for tornado warnings to 0.35. The report card score also improved to a passing grade of 56.6/100. Further exploration of the results showed enhanced performance for tornadoes that occurred within Doppler radar range, when the parent thunderstorm involved supercell processes, and for tornadoes rated EF2 or higher. A number of recommendations are made aimed at further improvements to tornado alerting performance.