Are tornadoes considered severe weather or extreme weather?

They can actually be either depending on their intensity. ECCC defines severe weather as hail having diameter 2 cm or greater, 50 mm of rain in an hour or less, wind gusts reaching 90 km/h or greater, or tornadoes. These phenomena occur many times per year across Canada and are considered a regular part of our warm season climate.

However, climatologically extreme weather can also occur; that is, severe weather phenomena having a size or intensity that has been very rarely if ever observed. Examples are violent tornadoes (EF/F4 to EF/F5) and softball-sized (or larger) hail that can only be generated by extremely intense supercell thunderstorms.