Dr. Kevin Trenberth on the tornadoes and excess precipitation

Excerpted from Bloomberg article by Brian K. Sullivan, May 23, 2011:

This year’s severe storms are the result of warm moist air from the Gulf of Mexico clashing with cooler air across the northern U.S., Samuel said.

The Gulf of Mexico is 3 °F (1.6 °C) warmer than pre-1970 levels, which means it can carry 12% more moisture, said Kevin Trenberth, distinguished senior scientist at the National Center for Atmospheric Research in Boulder, Colorado.

“Two degrees of that can be attributed to natural variability while one degree Fahrenheit is associated with climate change,” Trenberth said. “Some part of it is global warming-climate change and some part is natural variability.”

La Nina’s Influence

He said the La Nina phenomenon, a cooling of the Pacific Ocean, is also still focusing the storm track across the U.S. “just the right distance from the Gulf” to enhance tornado and severe thunderstorm development.

The Gulf moisture has also meant more rain than normal across the U.S. The Mississippi and Ohio rivers have set flooding records this year from Illinois to Louisiana.

“There has been enough rain in this event that there will probably be another bubble that will go down the Mississippi as well,” Trenberth said.

http://www.bloomberg.com/news/print/2011-05-23/tornadoes-severe-storms-kill-at-least-91-in-u-s-missouri-is-hit-hardest.html