Are Significant Tornadoes Occurring Later in the Year in Southern Ontario?

Abstract

More than a dozen tornadoes occur on average every year in the Canadian province of Ontario (ECCC, 2017). While most are weak in nature (i.e., rated F/EF0-1), a number of tornadoes having far greater intensity have occurred. For example, F4 tornadoes in 1946For example, F4 tornadoes in , 1970For example, F4 tornadoes in and 1985 resulted in 31 deaths and hundreds of injuries.Though tornadoes in Ontario have been recorded March to December, the peak months are May to August. Over the last decade or more, Ontario's severe weather community has noted anecdotally that tornadoes now seem to occur later in the season here. In fact, all three November tornadoes on record in Ontario occurred after 2004 (F/EF1 tornadoes in 2005, 2013 and 2020), and in 2018 an EF3 tornado developed as part of a 7-tornado outbreak in southern Ontario and neighboring Quebec in late September (Sills et al., 2020)-the first September F/EF3+ Canadian tornado in 120 years and the first tornado outbreak of such magnitude that late in the year in Canada.For this reason, the present study investigates the long-term trend in the month of maximum tornado occurrence in Ontario. It also looks for similar long-term trends using tornado data from neighboring US states.Though no past research work investigates this aspect of tornado climatology in Canada, studies on this topic exist in the United States. Long and Stoy (2014) found that, over the past six decades in the central and southern US Great Plains, peak tornado frequency has shifted earlier by 7 days. Lu et al. (2015) investigated tornado trends in the central US and their results also suggested that the seasonal peaks for both observed tornadoes and environments conducive to tornadoes now occur earlier in the year with a trend of 3.7 days per decade.Note that the Fujita (F) scale (Fujita, 1981) was used in Canada to 2012, and was replaced by the Enhanced Fujita

ERA5‐Based Significant Tornado Environments in Canada Between 1980 and 2020

“…Nonetheless, it is shown that Canadian Prairie strong tornadic storms are more dominated by thermodynamic and buoyant energy influences compared to larger wind shear influences in eastern regions. We suspect eastern Canada has stronger dynamics and winds at all levels partially due to more Spring and Autumn events that typically have well‐developed synoptic systems and over all less CAPE Future analysis will compare summer versus spring/autumn environments, since southern Ontario has been experiencing more late‐season events (Sills et al., 2022) and future cool‐season tornadoes may be stronger (Woods et al., 2023).…”