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News — What's the difference between sleet and freezing rain? What's a snow squall? And does the term “polar vortex” mean we’re in for a really deep freeze all season? Paul Roebber, one of the  in the United States and the world, can help explain weather terms more commonly heard in wintertime. Roebber is a and founder of the Innovative Weather forecasting service at the University of Wisconsin-Milwaukee. He can discuss subjects like the true effects of the polar vortex, a pattern of high-level winds that circles the North Pole year-round, even on the hottest summer day. Roebber  has improved over the past couple of decades as computer modeling has improved both in speed and accuracy. He’s a leader in bringing new approaches to meteorology, and his research has changed how experts around the world forecast weather.