Tornadoes don’t hop, jump or skip. They can retreat back up into the clouds and spawn again sometime later. They can carve a path through a neighborhood that spares some houses and demolishes others. This leaves the impression the tornado skipped houses. While it’s true a tornado can completely destroy one house and minimally damage another right next to it, the reason has nothing to do with jumping or skipping.
It does have to do with the internal structure of the tornado and its path. The funnel of a tornado is sometimes composed of two or more vortexes. Think of a larger tornado having multiple smaller tornadoes inside of it. This kind of tornado is called a multiple-vortex tornado and is almost always responsible for narrow paths of extreme destruction. We normally can’t see the individual vortexes because condensation and debris obscure the internal structure. This is what gives a tornado that wedge shaped appearance.
Even though a tornado can be a hundred yards or greater in width, these smaller vortexes may only be a couple dozen feet in diameter and follow one another, often referred to as “training”. The winds in the vortexes can easily spin in excess of 200 mph and are actually responsible for a majority of a tornado’s destruction.
Since these vortexes are only a couple dozen feet across, they represent a smaller portion of the entire tornado funnel. As the tornado moves into a neighborhood, almost all the houses will suffer some damage from flying debris and the surrounding winds. However, those that get hit by a vortexes will suffer far greater damage. That means one house may be totally destroyed while the house across the street may have considerably less damage. This is the main reason why it looks like a tornado may skip over one house while completely destroying the one right next to it.
A large tornado’s destruction can vary significantly in just a quarter mile or so. As an example, one neighborhood might experience destruction consistent with an F3 tornado. By the time the tornado crosses into the next neighborhood, the intensity might have dropped down to an F1. A short time later, it could re-intensify back into an F3 or greater. The neighborhood lucky enough to experience F1 strength destruction will suffer far less damage compared the to other areas that experienced the F3 intensity. This may give the appearance the tornado skipped over one neighborhood while inflicting heavy damage to the other neighborhoods.
Because of the above reasons, damage reports vary for the same tornado event which make classifying the tornado on the Fujita Scale (the F-Scale) difficult. A new enhanced F-Scale will be implemented starting February 1st, 2007 to address this problem and make tornado reporting more accurate.