Extreme heat has gripped the US West over four of the past five weeks

Western states faced a fourth extreme temperature event in five weeks, with temperature records broken

An intense heatwave gripped the United States over the past weekend, in what was billed as the fourth extreme heat event in five weeks for the region.

On Friday, a ridge of high pressure built over Utah, Colorado, New Mexico and Nevada, forming a high-pressure heat dome that forecasts thought would break records for its size, according to The Washington Post.

In what was described a rare heat dome event, the phenomena was forecast to reach 600 dekameters, or about 20,000 feet, in size before heading northwest before Monday.

It was also expected to be two American football fields bigger than an average heat dome event.

Heat domes form when a mass of hot air expands up into the atmosphere forming a “dome” that diverts other weather systems around it, and also creates its own heat, in what is a recurring cycle of heat.

The high pressure was expected to bring temperatures 20 to 30 degrees above July averages for swathes of the western US on Saturday, where abnormally high temperatures have already been seen in recent weeks, and where wildfires are being fuelled by the rising warmth.

The heatwave was also expected to reach parts of British Columbia and Alberta, as well as Saskatchewan and Manitoba, at the weekend. A similar event in late June killed around 500 people in Canada, and 200 in the northwestern US.

Warnings for extreme heat were widespread toward the end of last week, with the US National Weather Service in Great Falls, which covers north central and southwest Montana, warning of temperatures in the region of “105 and 110 in a few locations, so extreme heat remains possible”.

On Saturday, 104 F (37.7 C) was recorded in Mizpah, Minnesota, with the heatwave stretching into Monday, when a high of 110 F was recorded in the state’s Glasgow-Valley County. On Tuesday, officials said thunderstorms were expected.

Among the extreme temperatures recorded in the last month are 117 F (42.2 C) in Las Vegas, Nevada, which was its highest ever temperature. And in Salt Lake City, Utah, thermometers have so far topped 100 F 15 times this year.

If governments around the world, as well as in the US, fail to stop a further rise in average temperatures – which are already 34 F (1.2 C) higher than at the beginning of the industrial era – then extreme weather events such as this weekend’s heatwave are set to become more frequent.