© 2009, 1998 WGBH Educational Foundation. All Rights Reserved.

Adapted from NOVA: "Warnings from the Ice". A NOVA Production by Gardner Films, Inc. for WGBH/Boston in association with Sveriges Television. Third party materials courtesy of Atmospherics, Inc., Mark Twickler, NOAA National Severe Storms Lab, and Peace River Films, Inc. Animation courtesy of Schwartz/Giunta Production Company.