Tornado Damage: Why Is One House Destroyed, While Next Door Neighbor Is Fine?

Tornado damage in Hanover, Indiana Thursday.
The destroyed house was likely hit by a subvortice
within the main tornado. That subvortice
missed the house next door, which looks fine. 

 I'm sure a lot of you have noticed it. 

Whenever there's news of a damaging tornado on TV, you'll often see one house blown to pieces while the next door neighbor's home looks fine. 

I've always been fascinated (with a sense of dread) of that kind of thing. The luck of the draw. The fickle finger of fate. Something like that. 

There's actually a well-known scientific reason for this pattern of destruction. To understand it, you need to picture a Tilt-A-Whirl at the county fair. 

There's a video of a Tilt-A-Whirl if you click on this link.  The entire amusement park ride is rotating, while individual car also spins. Notice how the car usually spins faster when the direction of the spin is the same as the ride's spin.

The cars on the Tilt-A-Whirl spin more slowly when its rotation is in the opposite direction of the overall ride.

The house on the left was likely destroyed by a subvortice
within a parent tornado. The house across the street was
damaged more by debris from the destroyed home than
the actual wind. Other houses in the 
neighborhood look nearly unscathed. 

In one respect, tornadoes are often giant Tilt-A-Whirls.  You have one rotating tornado, the ride itself. Inside that tornado are what are known as subvortices or suction vortices.

These vortices are little tornadoes circulating within the main twister. They are the "cars" on the Tilt-A-Whirl.

Just like those Tilt-A-Whirl cars, the wind speed is much stronger in the part of the subvortice that is spinning in the same direction as the main tornado. 

Winds are lighter in the part of the vortices that's rotating in the opposite direction of the big tornado it's playing with. 

 These subvortices are small, often just a few yards wide. The result of all this is you get little lines or arcs of severe damage where the subvortice was spinning in the same direction as the tornado.

 These little streaks of damage can be the result of winds blowing as much as 100 mph more than in the general circulation of the main twister

Which is why you see one house destroyed by a tornado while the next door neighbor pretty much has to rake up a few leaves to clean up after the storm. 

Unless the subvortice flings debris at something or someone. Sometimes, like in the second photo in this post, the debris from a house destroyed by a suction vortices smacks into the neighbor's house, causing damage there as well. 

 It's unknown what percentage of tornadoes have these subvortices, but it's a lot. Maybe even most tornadoes.

They're usually hard to see, but if a tornado hasn't really condensed into a thick funnel, you can often see the subvortices dancing around the main circulation. 

Famous storm chaser Reed Timmer has a video of tornadoes with quite visible sub-vortices to give you an idea how they act. Click on this link to view, or if you see the the image below, click on that.