Preliminary readings of sites in Arizona and southern California indicate that the US has suffered its hottest March day on record.
Large parts of the southwest of the United States are trapped in a dangerous heatwave, made worse in some places by a heat dome, with temperatures reaching around 43C (110F) at testing sites.
The heatwave has shattered March temperature records all over the southwest of the country, with hot weather arriving months ahead of schedule.
"This is what climate change looks like in real time: extremes pushing beyond the bounds we once thought possible," said University of Victoria climate scientist Andrew Weaver.
March's heat would have been virtually impossible without human-caused climate change, according to a report released today by World Weather Attribution, an international group of scientists who study the causes of extreme weather events.
The area of the US being hit by extreme weather in the past five years has doubled compared with 20 years ago, according to the National Oceanic and Atmospheric Administration's Climate Extremes Index.
The extreme conditions are expected to persist and expand east in the coming days.
Across Southern California and the Desert Southwest, around 38 million people are under heat alerts.
Phoenix recorded its earliest triple-digit day on Wednesday, with a high of 38.8C (102F).
Temperatures in the city reached 40C (104F) on Thursday.
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"This is not only the first 100F (37.8C) day of 2026, but it is also the earliest occurrence of 100° in Phoenix (which last occurred on 26 March 1988)," the local office of the National Weather Service wrote on X.
Phoenix is forecast to hit 41C on Friday and Saturday, with an extreme heat warning in effect for the region.
Las Vegas in neighbouring Nevada also saw a new March record, with temperatures reaching 35C.
Temperatures could reach 37.7C there today.
Records could also be set in Colorado, as this week's heat dome continues to trap hot air over the southwest of the country.
(c) Sky News 2026: US suffers hottest March day ever recorded as heat dome drives up temperatures
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