A team of researchers led by Andrew Mercer of Mississippi State University found two factors are crucial: whether a storm has high wind shear -- the change in wind speed and direction with height -- and high "helicity," a measure of how much the storm tends to rotate, ScienceNews.org reported Monday.
Most research has focused on storms known to have triggered twisters, and trying to identify why, but many strong storm systems never create actual tornadoes although they can cause harm through high winds, hail or other hazards.
"Now we can say, 'Yes, this is what a tornadic outbreak looks like, generally speaking, versus a non-tornadic outbreak,'" Mercer said.
In a paper analyzing 50 tornadic and 50 non-tornadic storms, scientists reported it might be possible to identify the differences between the two up to 24 hours before tornadoes are spawned.
Studying more storms should help scientists improve their ability to predict tornadoes, another meteorologist said.
"We're trying to go after that portion of the severe weather occurrences that we think we have a reasonable chance of being able to forecast," Chuck Doswell at the Cooperative Institute for Mesoscale Meteorological Studies at the University of Oklahoma said.