The Storm Prediction Center and local National Weather Service offices did a terrific job highlighting the dangers of this weather systems. For several days in advance, residents of Mississippi and Alabama knew they were under the gun for tornado-producing thunderstorms.
The storms April 27 were fueled by strong wind shear due to a low-level jet stream from the south and a southwest-to-northeast flowing stream of high speed winds aloft. This created the wind shear (change of wind direction and/or wind speed with height) that provided strong lift and rotating supercell thunderstorms. The storms were moving very fast - up to 50 miles per hour in some cases. So many of these tornadoes could have simply reached people before they had a chance to get to shelter.
Power was also out when many of the tornadoes struck. That's because morning storms knocked out power and even broadcast towers for NOAA Weather Radio. When the afternoon storms struck, some people had to rely on text message warnings from the National Weather Service or their favorite TV station. And even some cell towers were destroyed in the first wave of storms.
And finally, so many of these tornadoes were powerful, probably EF3 or higher. When winds exceed 165 miles hour (EF4) or 200 miles per hour (EF5), there may be no way to escape. Even if you are in a place of safety, homes can be scraped clean off their concrete slabs. (Many homes in the south do not have basements.)