* Photo: Danielle Maxwell * In hill country from Iowa to the Scottish Highlands, sky-gazers have reported some strange, ominous-looking clouds of late. Dubbed undulatus asperatus (turbulent undulation), the atmospheric anomaly could be headed where only 80-odd clouds have gone before: into the International Cloud Atlas. If it makes the cut, asperatus will be the first new addition in more than 50 years.

Where did it come from? Gavin Pretor-Pinney, president of the UK-based Cloud Appreciation Society, has a theory: "It's warmer, moister air above and colder, drier air below, with an abrupt boundary in between." Add wind passing over rolling terrain and "you get the same wavy effect as on the surface of water."

The formation has probably been around for a long time, but it's only now getting attention: "Before the Internet and digicams, people might have mentioned it to a few friends and that would be it," Pretor-Pinney says. "Once the news got out, I was inundated with emails saying, 'I saw it three years ago; here's the picture!'" He's charting those images against atmospheric conditions to document the cloud's unique characteristics. The next step: Storm Geneva to seek formal recognition from the World Meteorological Organization.

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