What is a ‘heat dome’ and why is is it causing record-breaking temperatures in the US?

Western Canada and the US Pacific Northwest are suffering blistering heatwaves that have already caused dozens of deaths.

The provinces of British Columbia and Alberta are the worst affected areas in Canada, as well as parts of Saskatchewan, the Northwest Territories and the Yukon, all of which have been issued public health warnings.

The country recorded its all-time highest temperature for the third day in a row on Tuesday afternoon when the mercury hit a staggering 49C in Lytton, British Columbia, after previously reaching 47.5C on Monday and 46.6C on Sunday.