That used to be the thing to do, Kitty, but over the years, more information has come out that it really makes no difference. My opinion is that if you open the windows and the tornado doesn't destroy your house, you are going to have all sorts of things blown around inside your house, some of which weren't inside your house before the tornado.
I do not open my windows, but I do open the door...and go out to watch.
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Later edit
Scientists once thought houses exploded when a tornado passed over because of the really low pressure in the tornado. They figured that the higher pressure in the house would knock down the walls trying to get out. So they said you should open your windows to equalize the pressure. It turns out that more damage can be done by opening the windows. -
http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/tornado/myths.htmlIf the winds inside a tornado are strong enough to lift a car, train and scour asphalt off the road, then your windows being open or closed won’t make a bit of difference. The other argument that opening the windows on one side of the house and not the other might cause more internal air pressure because the air won’t have an escape out the other side is also false. The same principal applies. The glass window will give out far before the roof or walls do. Despite what some think, the air pressure differential doesn’t cause a house to explode during a tornado.
The air pressure differential between the inside of your home and inside of a tornado is not that great. The Texas Tech’s Institute for Disaster Research conducted several experiments and concluded that the pressure drop found inside a tornado with winds speeds of 260 mph (just shy of an F5 tornado) was only about 10%. That’s about 1.4 pounds per square inch which really isn’t that much. Most well built houses and buildings can vent this great a pressure change with no ill affects on the dwelling, even if all the windows and doors are closed. There are attic openings, chimneys, furnace vents, and other small openings underneath doors and closed windows for which the air can escape. It’s not the pressure differential that destroys a house when a tornado hits, even though it may look like the house is exploding. -
http://www.weatherimagery.com/blog/windows-and-tornadoes/In the past, it has been said that a tornado creates a vacuum of air pressure, and your home will suffer less damage if you open the windows. While it is true that tornadoes create a 'sucking' vacuum effect, you should not, under any circumstances, open your windows during a tornado. This will only allow the damaging winds into your home. -
http://www.associatedcontent.com/article/208797/the_body_of_a_tornado.htmlDO NOT open your windows. -
http://www.nssl.noaa.gov/edu/safety/tornado.html