A U-M spin-off named after a radical sixties group is an unlikely capitalist success story.

When Jeff Masters helped launch the Weather Underground as a private company in 1995, he never dreamed it would become the second-biggest weather resource in the country. “I figured maybe we’d have ten people a decade into the future and would run out of things to put on the website,” admits the unassuming Masters, one of four U-M grads who run the company. Yet today the site employs thirty-seven people and ranks second only to the Weather Channel’s weather.com in traffic. In January, Quantcast rated wunderground.com the fifty-seventh-largest site on the web, with 17 million unique visitors in the previous month.

Masters says the site’s radar scans, which can be set in motion to track the direction in which storms are moving, are a big draw. So is Masters’ own blog, a fascinating and readable account of the weather topics of the day. Hundreds of users, ranging from professional meteorologists to amateur hobbyists, contribute their own blogs. The Weather Underground also has the world’s largest network of “backyard” personal weather stations—more than 10,000 (the six in Ann Arbor include one at Leslie Park Golf Course and one at Loch Alpine)—plus more than a million user-posted weather photos and more than 1,000 webcams.

Though the company recently doubled its Ann Arbor office space on North Fifth Avenue, only five employees are based here, including Masters and co-founder Jeff Ferguson, a U-M computer science grad. Thirty-two (meteorologists, computer scientists, techies, and sales staff) work in San Francisco, where the other two working founders, Chris Schwerzler and CEO Alan Steremberg, moved in the mid-1990s. “At the time, the Bay Area was the only viable place to have a data center for an Internet start-up company,” explains Masters. “Bandwidth was too expensive anywhere else.”

Until this past year, the company had never spent any money advertising its website. Growth came by word of mouth, aided greatly by the millions of weather “stickers” the company has given away to any site that wants one (including the Observer’s site, arborweb.com). They update the local temperature hourly, and when clicked on take you to wunderground.com

The company grew out of weather-education efforts by U-M meteorology prof Perry Samson. Though he’s not an employee, Samson still sometimes works on special projects—he created the site’s interactive tornado map, which lets viewers see reports, radar tracks, and even photos of recent twisters.

The company’s whimsical name doesn’t even register as a pun today with most visitors. But one day in 1997, “when the website was in its infancy, I got a call from one of the original members of the Weather Underground,” laughs Masters. “I remember being a little nervous, since they were pretty radical, but she assured me she thought the website was great.”