Part 1 of the documentary I cut for Channel 4 about the tornado that hit Oklahoma in 2013. On 20 May 2013, a monster tornado swept through the US state of Oklahoma, killing more than 20 people, injuring hundreds more and flattening entire neighbourhoods. In the aftermath, this documentary investigates the terrifying power of the storms that produce the fastest and most destructive winds on Earth. British weather expert Alex Beresford travels through the devastation of the city where a number of people, including nine children in a school, died in a storm now rated as an EF5 tornado, the most dangerous of all of nature's furies. Alex interviews survivors, rescuers and the tornado scientists struggling to understand and predict how future storms may strike.