A twelfth of early and especially intense heat
This week, a vast high-pressure system is settling in permanently over the American West, forming a true “heat dome”. This mechanism acts as a lid in the atmosphere, trapping warm air and fostering its accumulation day after day under maximum sunshine. This atmospheric blocking, linked to a marked undulation in the jet stream, concerns a large territory ranging from California to Arizona, 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 shattered on Wednesday with 41°C in Palm Springs (California) and 38°C in Phoenix where the earliest 100°Fahrenheit was recorded. 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 and move 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 close to 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 worrying situation due to its speed and impacts
While heatwaves are common in summer in this region, their occurrence as early as March is highly unusual. American meteorological agencies already anticipate significant health consequences, due to bodies that are still poorly acclimated to the heat at this time of year. This early heat could accelerate the melting of the snowpack in the Rockies, exacerbating water scarcity issues and increasing the risks of drought and wildfires in the months to come.
Due to its early occurrence, intensity, and extent, this episode is already shaping up to be one of the most significant ever seen so early in the season in the western United States, once again highlighting the increasing power of extreme weather events.
