US scorches through hottest March day as heat dome traps Southwest

The United States has endured what may be the hottest March day ever recorded, as a brutal heatwave grips the southwest and pushes temperatures into midsummer territory months early.

Preliminary readings from monitoring sites across Arizona and southern California show temperatures reaching around 43°C (110°F). Officials warn the extreme heat — driven partly by a powerful atmospheric heat dome — could intensify and spread east in the coming days.

Heat Dome Locks the Southwest in an Early Season Furnace

Large parts of the desert southwest are now locked under a dangerous high-pressure system trapping hot air close to the ground.

Cities across Arizona, Nevada and California have smashed longstanding March records. Around 38 million people are under heat alerts as authorities warn residents to limit outdoor activity and prepare for conditions more typical of July than early spring.

In Phoenix, the heat arrived with unprecedented speed.

Phoenix Breaks a 38-Year Temperature Record

The city logged its earliest ever triple-digit day this week.

Temperatures hit 38.8°C (102°F) on Wednesday and climbed to 40°C (104°F) on Thursday, according to the local office of the National Weather Service. That beats the previous earliest 100°F reading, recorded on 26 March 1988.

Forecasts show the mercury rising further, with Phoenix expected to reach 41°C and remain under an extreme heat warning through the weekend.

Records Collapse Across the Desert West

The heatwave is not confined to Arizona.

In Nevada, Las Vegas surged to 35°C, setting a new March temperature record, with forecasts suggesting 37.7°C could follow. Meteorologists warn additional records may fall across Colorado and neighbouring states as the stagnant heat dome continues to trap scorching air across the region.

The scale of the event has alarmed climate scientists.

Scientists Warn: Extremes Are Accelerating

Researchers say the scale and timing of the heat would have been “virtually impossible” without human-driven climate change, according to a new analysis by World Weather Attribution.

Climate scientist Andrew Weaver of the University of Victoria said the surge shows how rapidly extremes are shifting. Data from the National Oceanic and Atmospheric Administration indicates the share of the US experiencing extreme climate events has doubled in the past two decades.

With the heat expected to push further east, forecasters warn the record-breaking temperatures may only be the beginning.

US suffers hottest March day ever recorded