BBC Four HD Thursday

Dr Helen Czerski finds out how advances in technology are giving new insights into tornados - the fastest winds on the planet

Singer Kelly Clarkson explores her mother's side of the family, uncovering the story of her great-great-great-grandfather, who fought against slavery during the American Civil War

The people and animals who inhabit Iceland, including an Arctic fox family eking out a clifftop living and Viking horsemen taking to the saddle for the autumn round-up

Two New York cops use unorthodox methods to break a drug ring smuggling heroin into the US from France. Oscar-winning fact-based thriller, with Gene Hackman and Roy Scheider

An obsessive electronic surveillance expert makes the unprofessional mistake of getting personally involved in a dangerous case. Thriller, starring Gene Hackman and John Cazale

Critic Mark Kermode examines the making of classic thriller The French Connection, beginning with the history behind the 1960s drug bust that inspired the film

Film-maker Karl Taylor and his team investigate what happened to the German submarine UC18 and Royal Navy Q-Ship the Lady Olive

British grandmasters Dan King and Ray Keene offer tips on playing chess, taking viewers through a special demonstration game from opening gambit to checkmate

Singer Kelly Clarkson explores her mother's side of the family, uncovering the story of her great-great-great-grandfather, who fought against slavery during the American Civil War