There are some small regions in the United States which experience unexpected
high tornado frequency, and also areas with unexpected low frequency of
For example, Hall County has a tornado density of 124.5 twisters per 1,000 square miles. However, Lancaster and Dodge counties have only 35.8 and 35.5 tornadoes per 1,000 square miles.
These "holes" in the broader map of tornado distribution and concentration are mostly due to chance and randomness, not some physical or topographical condition.