President Obama will visit Missouri Sunday to meet with victims of the storm and speak with emergency officials. Speaking from London, where he is on the second leg of a six-day European trip, Obama said he wanted to let the storm’s victims know “that all of America cares deeply about them and that we are going to do absolutely everything we can to make sure that they recover.”
Added to the record 875 tornadoes that tore across the country in April, this latest disaster has experts asking why 2011 has spawned so many deadly storms. While researchers suss out the causes for this year’s record-breaking season, one thing is certain: Unusually big twisters are blasting through heavily populated areas.
“We have had more F4s and F5s than in past years,” said Jack Hayes, director of the National Weather Service, referring to the two most destructive categories of tornadoes. And instead of touching down in farms and fields, storms have hit cities such as Joplin and Tuscaloosa, Ala.
An emerging body of research points to a cyclical drop in temperatures in the Pacific Ocean as part of the answer. Called La Nina, the cycle lasts at least five months and repeats every three to five years. This year La Nina is pushing a strong North American jet stream east and south, altering prevailing winds. The jet stream’s river of cool air high in the atmosphere pulls warmer, more humid air from the ground upward, forming thunderstorm “supercells.”
Such a pattern drove the outbreak of more than 300 tornadoes that swept from Mississippi to Tennessee in late April, killing at least 365, experts say. But it’s too early for them to know whether La Nina alone accounts for what is shaping up to be a disastrously record-breaking tornado season, said tornado expert Grady Dixon of Mississippi State University. “La Nina is probably part of it,” he said. “But it’s not the only reason.”
Tornado experts predicted a devastating season this year, and many have begun studying whether global climate change is driving more frequent — and more intense — tornado-spawning thunderstorms. Such work is at an early stage, making it difficult to draw conclusions.
“This will be a rich topic of research in the coming years,” said Russell Schneider, director of the Storm Prediction Center in Norman, Okla., part of the National Oceanic and Atmospheric Administration.
Warm air, moisture and specific wind patterns are the deadly ingredients that mix together to form tornadoes, and climate change influences at least one of them by increasing the amount of moisture the air can hold.