There have been 20 in Waimate
it is unknown but the average tornadoes in the united states is over a thousand
It is called the Enhanced Fujita Scale: EF-0. Light damage Wind 65 to 85 mph. Causes some damage to siding and shingles EF-1. Moderate damage Wind 86 to 110 mph. Considerable roof damage. Winds can...
I'm not sure but since 2000 there was roughly about 7,000 that hit tornado ally.
Tornado Alley experiences and estimated 800 tornadoes each year.