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.
How much lead time you get will vary based on the weather, of course, but even a little extra time helps. This first real-world use warned western Oklahoma of likely tornadoes and hail about 30 minutes in advance, which may have minimized casualties.
Warn on Forecast isn't officially in use yet, as NOAA wants to refine the model. If it takes off, though, it could easily save many lives and help communities recover sooner. If you can reliably evacuate or reach a dedicated shelter, the focus is less on basic survival and more about preserving what you can.