The US is bracing itself for a potentially deadly heatwave as temperatures soar ahead of Independence Day celebrations. The prolonged heatwave, fuelled by a 'heat dome' phenomenon, threatens to scorch over 120 million people in its path, with forecasters warning that the extreme conditions will coincide with America's Fourth of July holiday weekend.
The heatwave is expected to intensify in the Midwest and Mississippi Valley through Thursday before shifting eastward towards the Ohio Valley and the East Coast. Temperatures are set to reach as high as 40.6C, while the 'heat index' – a measure of how hot it feels to the human body – could soar to between 38C and 46C. Daily temperature records are forecast to be broken on Thursday and Friday, with potential for some monthly and even all-time records to fall.
In response to the severe conditions, officials across affected regions are issuing strong warnings, advising residents to limit time spent outdoors, stay hydrated, and access air conditioning or cooling centres where possible. In New York City, Mayor Zohran Mamdani has activated a heat emergency plan, opening hundreds of cooling centres from Wednesday onwards. Similarly, Detroit is providing public access to air-conditioned recreation centres as temperatures are expected to reach 38C.
The extreme weather could also impact major events, including World Cup football matches in the US. The global players' union, Fifpro, has established thresholds for heat index values deemed unsafe for play. While stadiums in cities like Houston and Arlington offer air-conditioned comfort, fans travelling to and from venues or attending outdoor fan festivals will face significant heat exposure. In Philadelphia, parts of the Fifa World Cup Fan Festival are being moved into cooled tents on Thursday and Friday.
Canada is also experiencing its own heatwave, which began on Tuesday. Temperatures in Ontario are forecast to reach 37C this week, with Toronto hosting a World Cup game on Thursday when temperatures are predicted to hit 35C. Orange heat warnings have been issued for Ontario, while central and eastern parts of the province, including Montreal, are under yellow heat warnings.