Although a below ground basement is one of the safest places during a tornado, the southwest corner will provide no added protection unless there is more structural support as compared to the other corners. Anytime you can get below ground you are better off, but somewhat recent studies have shown that when a tornado passes over a house, debris tends to collect in all the corners of the basement.
The origins of this myth that the southwest corner is the safest spot could be attributed to the belief that tornadoes always come from the same direction — from the southwest — and travel northeast. It was believed that the debris will be thrown in a northeasterly direction. This simply isn’t true and placing yourself in the southwest corner on the premise the winds will skip or hop over you won’t increase your odds of survival unless by chance. Furthermore, taking the time to figure out which direction the tornado is coming from may prove fatal. It’s best just to get in the basement, pick any corner, and protect yourself with whatever sturdy furniture you might have within the room.
The fact is tornadoes are very dynamic in that their intensities, speed, direction of travel, and internal structures can vary significantly from one another. Some have multiple voritcies while others don’t. Some are large in size while others are narrow. Some have very high wind speeds while others don’t. Some move fast while others move more slowly. And most importantly they don’t always come form the same direction. All these factors will alter the damage patterns and trying to figure this out while the tornado is fast approaching could be fatal. It’s best just to get in the basement, pick a corner, and protect yourself with whatever sturdy furniture you have in the immediate area.
This tornado myth started back in the 1950’s when the government published several news reels to the public that the southwest corner of a basement provided the best protection during a tornado (11:37 mark on the video to the left). Back then, researchers knew very little about tornadoes. They didn’t know how they formed, how fast the winds were or their internal structure. They were right in that basements provided good protection, but I’m not sure what the thinking was about the southwest corner. As mentioned above, maybe they thought the winds and debris would skip over a person who happened to be huddled in the southwest corner because most tornadoes came from that direction.
In general, the safest place during a tornado is in specially designed tornado shelters, one in which a door opens to a room below ground. If that isn’t an option, a basement would be the next best thing. Pick a corner and protect yourself with whatever sturdy furniture you can. If neither of these options is available then hunker down in an interior room with no windows, such as a bathroom or closet. If in a bathroom, get in the bathtub and pull as many pillows and blankets on top of you as possible. However, in the larger tornadoes you will need to be below ground as anything and everything can be destroyed leaving only the concrete foundation.