Oklahoma tornado: how did it form and why was it so deadly?

Briefing Tue 21 May, AT 16:07

Twister was a category four storm that struck the suburb of Moore with just five minutes' warning

Oklahoma tornado: storm chasers' video

Video Tue 21 May, AT 10:03

Clip captures the violent storm as it rips through a residential neighbourhood of Oklahoma City

Oklahoma tornado disaster: five questions answered

Summary Tue 21 May, AT 08:32

'Twister' with winds of 200mph flattens schools, houses and churches, leaving at least 90 dead