Deadly tornadoes have claimed the lives of at least 30 people in the Southern and Midwestern U.S. this week, with more twisters expected. The death toll is already at about half of the national yearly average.
One of the reasons these storms are so deadly is that scientists still struggle to predict exactly how or when they will form. Beyond that, it's incredibly difficult to predict what path they will take.
According to the National Oceanic and Atmospheric Administration, the average time between a warning and the arrival of a tornado is about 13 minutes -- enough time to seek shelter, but not nearly enough to evacuate a neighborhood or town. Official tornado warnings indicate a twister has actually been spotted; a tornado watch indicates the weather conditions make it possible tornadoes could form.
"Tornadoes can happen at any hour of the day and any time of the year, though they are most common in the spring, especially during May and June in North America," explains National Geographic's Brian Clark Howard in an article explaining what is known about the way tornadoes form.
Weather balloons, radar and on-the-ground observations have gradually improved tornado warnings from about 5 minutes in the 1980s to the current 13 minutes, but there is still a long way to go. (The lead-time is actually closer to 18 minutes when officials put out a warning - but they only manage to do so about 80 percent of the time.)
Meteorologists at the National Weather Service and other organizations are continually seeking ways to lengthen the warning time to a timeframe that gives residents a better chance of survival.
The NWS's Warn-on-Forecast project relies on software to sift through data on atmospheric temperature, moisture and other variables. One of the project's lead meteorologists, Harold Brooks, explained that the system is far from perfect. Sometimes it "makes really good forecasts, and other times it doesn't," he told National Geographic. He says improved software and faster computers will eventually improve the system.
Another possible way to predict their paths is to send drones into the storms, according to researchers in Oklahoma's state universities. They say this technique could advance the warning time by several hours. But with the government still heavily restricting the use of drones, meteorologists are not yet at liberty to unleash drones into brewing storms.
Even so, scientists at the University of Oklahoma and Oklahoma State University are researching the possibilities.
"We have the [unmanned aircraft] expertise, we have the weather expertise and, by golly, we have the weather," Stephen McKeever, Oklahoma's state secretary of science and technology and a vice president for research at OSU, told the L.A. Times in June 2013. "In many senses we're the perfect laboratory to do this kind of thing."
Tornadoes are among the hardest types of storms to predict because the conditions that lead to tornadoes form incredibly quickly. Hurricanes and blizzards show up on satellites days in advance, giving meteorologists more advance warning. However, tornadoes form much more rapidly.
University of Washington atmospheric sciences professor Cliff Mass told CBS News in 2013 that he believes that it may be possible to increase the advance time for a tornado warning to as much as three hours, though he doesn't know if meteorologists can do better than that. "I think six hours or eight hours is going to be very hard," he said.