To understand how this myth got started, you have to know a little about atmospheric pressure, which is the force exerted on an object by the air above. It can vary depending on factors like elevation and temperature, but the standard pressure at sea level is 29.92 inches of mercury (1,013.2 hPa) [source: National Weather Service]. While the pressure can drop as low as 25.7 inches of mercury (870 hPa) in tropical systems like hurricanes or typhoons, the lowest pressures of all are found at the center of tornadoes [source: Arizona State University]. One research team observed readings as low as 20.3 inches of mercury (688.4 hPa) at the center of a 2007 Tulia, Texas, twister [source: Blair et al.].
So what does this have to do with the window myth? Well, the thinking was that the difference between the low pressure inside a tornado and the higher pressure in the house would cause the home to explode like an overfilled balloon. So the experts advised residents to open their windows when a twister approached to help equalize the pressure. But as researchers looked more closely, they found that what lifted roofs off houses wasn't some kind of pressure bomb, but wind that got inside. So, ironically, opening the windows actually made things worse.
The moral of the story? If a tornado strikes, don't waste your time running around opening all the windows. In fact, stay away from the windows and find shelter in an interior room.