Most observers agree that this spring's spate of killer tornadoes is highly unusual by statistical and historical standards. After that, the disagreement starts. Is it a fluke? -- or a sign of La Nina or climate change? Why haven't better warnings helped?

"The threat of a catastrophic release of radioactive materials from a spent fuel pool at Japan’s Fukushima Daiichi plant is dwarfed by the risk posed by such pools in the United States, which are typically filled with far more radioactive material, according to a study released on Tuesday by a nonprofit institute."

"A series of storms struck Oklahoma, Kansas and Arkansas late Tuesday and early Wednesday, wiping out homes and businesses and killing at least nine people, emergency officials said."

"In a setback for the only model of nuclear reactor for which ground has been broken in the United States, government regulators have found additional problems with the design of its shield building, a crucial component, the chairman of the Nuclear Regulatory Commission said on Friday."

"The operator of the nuclear power plant at the center of a radiation scare after being disabled by Japan's earthquake and tsunami confirmed Tuesday that there had been meltdowns of fuel rods at three of its reactors."

"Rescue crews dug through piles of splintered houses and crushed cars Monday in a search for victims of a half-mile-wide tornado that blasted much of this Missouri town off the map and slammed straight into its hospital."

"The Grimsvotn volcano under the Vatnajokull glacier in Iceland was erupting Saturday, according to the Icelandic Meteorological Office." Some air travel disruptions are expected.

"The toll from a major tornado on Sunday in Joplin, Missouri has risen to 89 confirmed deaths, local officials said."

"U.S. government forecasters announced Thursday they expect three to six major hurricanes from an above-average Atlantic storm season."

"The president of Japan’s troubled power company, Tokyo Electric Power, resigned Friday, shouldering responsibility for the crisis at the Fukushima Daiichi nuclear plant as the utility booked one of the largest yearly losses in Japanese corporate history."