The United States, if I'm correct, has the most frequent and violent tornado activity in the world. What country comes second? And are there any historic tornado events from other countries I should know about?
Looking at the average number of tornadoes a year per 10000 square km, Holland gets far more tornadoes than the UK does.I have read in various literature that the United Kingdom (Great Britain)
especially England has the most tornadoes per sqaure mile as a country.
*I* personally think Australia and Canada are in "competition" for second place, but that's just my opinion.
many remain unreported or unconfirmed
I don't think there is competition there. Canada would get more large tornadoes than Australia. Australia gets alot of big summertime supercells but these as a general rule do not produce tornadoes.
Many of the tornado reports come from weaker convection in cold troughs crossing the southern parts of the country.
Does New Zealand get violent thunderstorms/tornadic storms, and if so, how often?