In case you're curious - I wanted to see what kind of trend we've seen.
(ignore the big blue square that's thinking outside the box; that was an accident.)
Source data here - which, following more or less in Tamino's footsteps, I extracted from NOAA's Storm Prediction Center's archived data, and from 2000+, year-by-year data, available as annual reports/maps - e.g. nationally for 2011, or, just for CA, e.g. for 2011 so far (11)
Apparently tornado detection is more sensitive than it used to be, so the apparent increase in numbers for Calif. might not reflect an actual increase.