There is a new article online about the special effects in Harry Potter.

Movie studios spend billions to morph strings of code into giant robots, flying superheroes, and apocalyptic mushroom clouds. Still, the toughest f/x challenge turns out to be the most elemental: re-creating Mother Nature. “There are not enough CPU cycles in the day to capture the complexity found in the environment,” says Industrial Light & Magic visual effects supervisor Tim Alexander. That hasn’t stopped him and his Oscar-winning team from trying. They crafted near-perfect CG waves for the Pirates of the Caribbean trilogy. But their assignment for Harry Potter and the Half-Blood Prince set the bar higher than ever: Mix fire with water. The clash of elements transpires when Harry Potter is rescued from sea-dwelling beasts by Dumbledore, who sets the ocean ablaze with a bolt of fire. Harry bobs to the surface only to find himself surrounded by a fiery tornado.