It's pretty simple: the longer you're out in the Plains the better your odds of seeing tornadoes. However, with each passing year we are finding that more and more folks simply cannot take off enough time to commit to a 10-day tour and our short tour formula has become, by far, the more popular. Hence, last year we began expanding our slate of 6- and 7-day offerings at the expense of our 10-day adventures. While it is true that your odds of any given "short" tour witnessing tornadoes will correspondingly decrease, the data does NOT suggest that the probabilities will be dramatically lowered. And you'll still get the same great, genuine storm chasing tour experience that you've come to expect from Silver Lining Tours.
Here is a separate article explaining some of the trade-offs of chasing in the "early" versus "late" season storm chasing.