The old belief behind opening windows was that the low pressure inside the funnel causes buildings to explode (because the totally destroyed homes were interpreted as exploding as most of the walls would fall out, not in) , so the idea was to open windows to equalize pressure. Of course, science has long proven that it all has to do with the severe winds, and that when the roof, or one wall goes and falls inward, the other walls fall outward. And every so often you hear that opening windows reduces glass breaking, or something. Either way, pressure has nothing to do with the damage, the tornado blows out the windows before then anyways, and that opening a window doesn't reduce glass going everywhere (not that glass even matters if it's something more severe then an EF2). Really, it just wastes time spent getting into shelter, which might already be limited.

Well, I wanted to be something of a professional, with a degree in meteorology, not just a hobbyist. So even if I did eventually make it to the needed math level, I really just don't like it enough to willingly do it all the time.