US Records Hottest March Day Ever as Heat Dome Intensifies Southwest
Preliminary readings from monitoring sites in Arizona and southern California indicate that the United States has experienced its hottest March day on record. Large portions of the Southwest are currently trapped in a dangerous heatwave, exacerbated in some regions by a heat dome, with temperatures soaring to approximately 43°C (110°F) at testing locations. This unprecedented heatwave has shattered March temperature records across the Southwest, arriving months ahead of the typical seasonal schedule.
Climate Change in Real Time
"This is what climate change looks like in real time: extremes pushing beyond the bounds we once thought possible," stated Andrew Weaver, a climate scientist at the University of Victoria. According to a report released today by World Weather Attribution, an international group of scientists studying the causes of extreme weather events, March's extreme heat would have been virtually impossible without human-caused climate change.
Understanding the Heat Dome Phenomenon
A heat dome is loosely defined as an area of high pressure that remains stationary over a specific region for days or even weeks. Hot air becomes trapped underneath, similar to a lid on a saucepan, driving temperatures well above normal for the time of year. The heated air expands upward into the atmosphere, where high pressure from above acts as a lid, preventing escape and causing the air to subside or sink, creating a dome effect. As the warm air sinks, it compresses and heats further, trapping more heat underneath while clouds are pushed around it, intensifying the retention of heat.
Expanding Impact and Historical Context
The extreme conditions are expected to persist and expand eastward in the coming days. Across Southern California and the Desert Southwest, approximately 38 million people are currently under heat alerts. According to the National Oceanic and Atmospheric Administration's Climate Extremes Index, the area of the US affected by extreme weather in the past five years has doubled compared to two decades ago.
Record-Breaking Temperatures Across Cities
Phoenix recorded its earliest triple-digit day on Wednesday, with a high of 38.8°C (102°F). Temperatures in the city escalated to 40°C (104°F) on Thursday. "This is not only the first 100°F (37.8°C) 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 reported on social media. Phoenix is forecast to reach 41°C on Friday and Saturday, with an extreme heat warning in effect for the region.
Las Vegas in neighboring Nevada also set a new March record, with temperatures climbing to 35°C, and projections indicate they could reach 37.7°C today. Additional records may be set in Colorado as the heat dome continues to trap hot air over the Southwest, underscoring the severity and persistence of this weather event.
