Original sentence: Six medium to large size Canadian cities were hit by significant strength tornadoes during the 20th century which caused large-scale damage and fatalities, in Regina (1912), Windsor twice (1946 and 1974), Sarnia (1953), Sudbury (1970), Barrie (1985) and in Edmonton (1987)
Edited sentence: Seven medium to large size Canadian cities were hit by significant strength tornadoes during the 20th century which caused large-scale damage and fatalities, in Regina (1912), Windsor twice (1946 and 1974), Sarnia (1953), Sudbury (1970), Woodstock (1979, by 2-F4s), Barrie (1985), and in Edmonton (1987)