Researchers at the University of Missouri-Columbia, studying 56,457 tornadic events from 1950 to 2011, said they found a 20.3 increase in tornadoes rated EF-2 to EF-5 on the Enhanced Fuijta scale when Pacific Ocean temperatures were warmer than average.
In addition, they said, the tornadoes that occurred when surface sea temperatures were above average were usually to the west and north of tornado alley, the area in the U.S. Midwest that experiences more tornadoes than any other area.
Cooler sea surface temperatures saw more tornadoes tracked from southern states like Alabama into Tennessee, Illinois and Indiana, they said.
"Differences in sea temperatures influence the route of the jet stream as it passes over the Pacific and, eventually, to the United States," MU graduate student Laurel McCoy said. "Tornado-producing storms usually are triggered by, and will follow, the jet stream.
"This helps explain why we found a rise in the number of tornadoes and a change in their location when sea temperatures fluctuated."
"Now that we know the effects of [Pacific Ocean] cool and warm phases, weather forecasters have another tool to predict dangerous storms and inform the public of impending weather conditions," McCoy said.