Tornado-day climatology of Manitoba 1980-1999

Although not frequent, tornadoes are common across Manitoba in the summer. There are on average 5.1 tornado days each year in Manitoba. The earliest report of a tornado was in 1868. Tornadoes have been reported as far north as Churchill. Past studies have determined that tornadoes are a significant public safety and economic concern for society. Analysis of their recent temporal and spatial occurrence update the level of risk for use by many sectors (e.g. emergency preparedness, insurance, general public). Anticipated possible increases in tornado frequency due to climate change (Etkins, 1995) highlight the importance of understanding tornado climatology and the associated risks. There have been several studies of tornadoes in Manitoba in the last four decades (Lowe and McKay, 1962; Shannon, 1976; Raddatz et. al., 1983; Raddatz and Hanesiak, 1991). These studies suggest that the number of tornadoes reported each year is increasing but the actual occurrence of tornadoes may not. It is generally believed that even today, there are two to three times more tornadoes occurring than are reported. There are several reasons, including: low population density; night-time occurrence; minimal damage; and other tornado data collection issues, such as poor reporting due to lack of or poorly trained observers. Furthermore, few detailed inspections of tornado damage have been undertaken in Manitoba, which leaves considerable uncertainty about the details of each tornado such as time of occurrence, path, duration and intensity. In this study, days with reported tornadoes were used to quantify the tornadic risk in Manitoba. The study focused on tornado days from 1980 to 1999. The days were grouped by Census Divisions and a risk analysis, similar to that done by Raddatz and Hanesiak (1991), was carried out.