Historic Heat in the United States: Records Shattered, Up to 43°C in March in California and Arizona

One fifth of the intense early heat dome This week, a vast anticyclone settles in the western United States, forming a true “heat dome”. This mechanism acts as a lid in the atmosphere, trapping warm air and promoting its accumulation day after day under maximum sunshine. This atmospheric blockage, linked to a marked undulation of the jet stream, affects a large area ranging from California to Arizona, passing through Nevada and New Mexico, with an extension towards the Rockies. Result: temperatures soar dramatically, with anomalies reaching +15°C compared to seasonal norms. This situation is all the more remarkable as it occurs just as winter is coming to an end.

Summer temperatures in the middle of March In the most exposed areas of southern California and Arizona, temperatures exceed 40°C, with peaks expected to reach 43°C. The first heat records were broken on Wednesday with 41°C in Palm Spring, California, and 38°C in Phoenix, where the earliest recorded 100°F temperatures were observed. Many heat records will be broken by the weekend, with even April heat records likely to fall.

Heat records in the USA © Meteo Consult / La Chaine Météo

The intense heat will quickly spread to the great plains of the American Midwest, moving further north: temperatures of up to 30 to 33°C are expected in regions located at latitudes comparable to those of Western Europe, where seasonal norms are around 10 to 15°C. According to several forecasts, nearly three quarters of the country could experience significantly higher temperatures in the coming days, highlighting the exceptional extent of this episode.

A concerning situation due to its precocity and impacts While heatwaves are common in summer in this region, their occurrence as early as March is very unusual. American meteorological organizations already mention significant health consequences, due to organisms still not acclimated to the heat at this time of year. This early heat could accelerate the melting of the snowpack in the Rockies, worsening water shortages and increasing the risks of droughts and fires in the coming months. Due to its precocity, intensity, and extent, this episode is already shaping up to be one of the most significant seen in the summer season in the western United States, once again illustrating the increasing power of extreme weather events.