A series of tornadoes struck the central United States this week, including a powerful storm in Oklahoma that killed at least 24 people. Marshall Shepherd, the president of the American Meteorological Society, describes the ingredients of major tornadoes, and how they are predicted.

Scientists say climate change could increase pests and weeds, lengthen growing seasons and turn dry soil to dust. Farmers are already on the offensive, adopting no-till cropping methods to conserve water and experimenting with different seeds. And scientists are using a technique called gene silencing to develop new crops--without tinkering with the plants' DNA.

Last year scientists reported that a skin cancer drug appeared to reverse the effects of an Alzheimer's-like disease in mice. But four studies out this week in Science question the original results. Ronald Petersen, director of the Mayo Clinic's Alzheimer's Disease Research Center, talks about the new findings, and the hunt for Alzheimer's drugs.

Smartphones, tablets and computers could help seniors stay connected to their communities and families. But a hefty price tag, steep learning curves, and designs meant for younger eyes and hands could keep some older adults from logging on. Guests discuss the best ways for seniors to tackle new technology, and how devices can be adapted to accommodate older users.

North Carolina State University biologist Rob Dunn and colleagues surveyed people's pillow cases, refrigerators, toilet seats, TV screens and other household spots, to learn about the microbes that dwell in our homes. Among the findings, reported in the journal PLoS One, homes with dogs had more diverse bacterial communities, and higher numbers of "dog-associated" bacteria.

Itch can be a useful warning sign, or a maddening symptom with no cure. But the origins of itch have long been a mystery. Scientists think they've come closer to understanding the origins of itch in a molecule that makes mice scratch like mad.

A new study unravels the mystery of a peculiar transformation: sometime in the 1990s, the insects developed a sudden aversion to sweet-tasting poisons.

Officials are forecasting that hurricane activity will be "above normal" this season, with 13 to 20 named storms. As many as six of those could be major hurricanes. Warm ocean waters and the lack of El Nino conditions are partly to blame.