Meteorologists usually only issue warnings for tornadoes when they're imminent, which gives you precious little time to take cover -- the American average is just 13 minutes. NOAA researchers may soon give you much more time to get to safety, though. They recently conducted the first practical test of a new model, Warn on Forecast, that gives you up to 3 hours' notice. The technique merges radar, satellite and surface data into a highly detailed prediction model. When you make frequent-enough predictions (every 15 to 20 minutes), you can tell when incoming weather patterns are very likely to trigger warnings.