March Heat Dome Shattered Records Across the West — and Scientists Say Climate Change Made It 800 Times More Likely

The bank thermometer outside a Phoenix strip mall flashed 101 degrees shortly after noon, its red digits shimmering in the glare. Parents hustled children from sun-baked parking lots into air-conditioned shops. A sign at the Camelback Mountain trailhead warned that popular routes were closed because of “extreme heat.”

It was March.

A summerlike heat wave in the heart of spring

From the deserts of Arizona and California to the farm fields of Nebraska and the Missouri River valley, a dome of high pressure parked over the western and central United States in late March, driving temperatures more typical of early summer than the tail end of winter. Hundreds of long-standing March records fell. Some places saw readings that rival typical June highs.

Within days, a team of international scientists delivered a stark assessment: This level of March heat over western North America would have been “virtually impossible” without human-caused climate change.

In a rapid analysis released March 20, researchers with the World Weather Attribution group concluded that the heat dome that settled over the region around March 18–22 was made roughly 800 times more likely by the warming caused by greenhouse gas emissions. They found that climate change added about 4.7°F (2.6°C) to the intensity of the event.

“This is what climate change looks like in real time: extremes pushing beyond the bounds we once thought possible,” said Andrew Weaver, a climate scientist at the University of Victoria who was not part of the attribution team but reviewed its findings.

From blizzard to heat dome

The heat arrived suddenly. One week earlier, a major blizzard known as Winter Storm Iona had buried parts of the Upper Midwest and High Plains in snow and snarled travel. As that storm pulled away, the jet stream kinked and stalled, allowing a strong, stationary ridge of high pressure—sometimes called a heat dome—to build over the Southwest.

By March 18, temperatures across large swaths of California, Nevada and Arizona were running 20 to 30 degrees above the 30-year average. Forecast offices of the National Weather Service began issuing heat advisories and, in some locations, excessive heat warnings—bulletins more commonly associated with July.

On March 19, a weather station near Martinez Lake, Arizona, recorded 110°F (43.3°C), eclipsing what meteorologists had cited as the previous U.S. March record of 108 degrees set in Rio Grande City, Texas, in 1954. The following day, four locations in Arizona and California reached 112°F (44.4°C), state and federal meteorologists reported, likely pushing the national March record several degrees higher, though some readings awaited final verification.

Phoenix hit 101°F that week, marking the city’s earliest triple-digit day on record. The previous mark was March 26, 1988. Forecasts called for multiple days near 106°F—far above the city’s old March record of 100 degrees.

“I’ve lived here 25 years and we always told people March was the safe month—warm, but not dangerous,” said a Phoenix event planner who moved several outdoor weddings under tents and into the evening hours. “Now even that feels like it’s gone.”

Hundreds of records fell across multiple regions

The heat wave was not confined to the Southwest. By March 21–23, the high-pressure ridge expanded eastward. Thermometers climbed into the 80s and 90s across the southern and central Plains, upper Midwest and portions of the Mississippi Valley.

The National Centers for Environmental Information counted at least 479 weather stations that broke all-time March records for high temperature between Wednesday and Saturday of that week, along with nearly 1,500 daily records.

New statewide March records were reported in at least 14 states, including California, Arizona, Nevada, New Mexico, Utah, Colorado, Kansas, Nebraska, South Dakota, Wyoming, Idaho, Missouri, Iowa and Minnesota.

In Palm Springs, the mercury surged to levels more typical of June. The city tied, then appeared to surpass, its previous hottest March days with readings in the 104–108°F range, according to preliminary data. Desert communities such as North Shore and Thermal matched or topped the old U.S. March benchmark of 108 degrees before the Arizona readings overtook them.

“It’s really hard to even keep up with how extreme our extremes are becoming,” said Bernadette Woods Placky, chief meteorologist at the nonprofit Climate Central. “We are pushing extremes to new levels across all different types of weather.”

The attribution findings: rarer, hotter—and strongly linked to emissions

The World Weather Attribution team defined the event not by a single afternoon’s spike, but by the hottest five-day stretch of March daily maximum temperatures across a region spanning roughly from 30 to 45 degrees north latitude, from the Pacific Coast to the Rocky Mountains.

Using a combination of observations and climate models, the scientists estimated that in today’s warmed climate—about 2.3°F (1.3°C) hotter globally than in the late 1800s—an event of this intensity in March has about a 1-in-500-year chance of occurring in a given year.

To be conservative, the group adopted a 1-in-100-year framing in its public communications. But they stressed that in a world without human-driven warming, their statistical analysis suggests such an event would essentially not occur.

“Our best estimate is that climate change has increased the likelihood of this event by a factor of around 800 and made it about 2.6 degrees Celsius hotter,” said Clair Barnes, a statistician at Imperial College London and a co-author of the study. “Even though models tend to underestimate the observed trend in extreme heat, they still show a very strong influence of greenhouse gases.”

The group’s analysis also found that hot extremes in March across western North America have warmed faster than those in many summer months. In some parts of the region, the hottest March events today are up to 11°F (6°C) warmer than in a cooler baseline climate.

Impacts: closures, schedule changes, snowmelt and fire risk

That rapid shift is already changing how communities experience—and are forced to plan for—the transition from winter to summer.

In Phoenix, city officials activated heat protocols typically reserved for later in the year. Popular hiking routes on Camelback Mountain and other desert preserves were shut during the heat of the day when the Weather Service issued excessive heat warnings. Medics and park rangers reported multiple heat-related rescues.

The Cactus League, Major League Baseball’s spring training circuit in Arizona, shifted at least 11 games to later start times to avoid the hottest hours. Teams added extra hydration breaks and shade structures where possible.

Farther north, in the Rocky Mountains and Sierra Nevada, the early-season heat accelerated snowmelt. Hydrologists warned that an already meager snowpack in Colorado—the lowest since at least 1981—would shrink faster, potentially tightening summer water supplies and drying out forests sooner, heightening wildfire risk.

In the High Plains and parts of Texas, forecasters flagged “critical” fire weather conditions as high temperatures, low humidity and gusty winds coincided.

A public-health threat that arrives earlier

Heat waves are historically the deadliest form of weather disaster in the United States, surpassing floods, hurricanes and tornadoes. Public health researchers note that early-season heat events can be especially dangerous because people are not yet acclimated and may not be running air conditioners consistently.

“Your body expects a gradual ramp-up from winter to summer,” said a physician at a Phoenix hospital emergency department. “When you go from 70s one week to over 100 the next, that’s when we see people get into trouble.”

Comprehensive national figures for heat-related illnesses and deaths from the March event are not yet available. But longer-term data from federal agencies show a broader pattern: heat-related mortality has been rising fastest in the Southwest and Southeast, even as some cities and states expand cooling centers and outreach.

The March heat dome also fits into a wider trend of increasingly costly weather extremes. Federal data show the number and average cost of U.S. weather and climate disasters causing at least $1 billion in damage have roughly doubled in recent decades.

Craig Fugate, who led the Federal Emergency Management Agency from 2009 to 2017, said the country’s basic approach to risk may no longer be adequate.

“We built communities on about 100 years of past weather and assumed that was a good guide going forward,” Fugate said. “That assumption is starting to break. We were operating outside the historical playbook more and more. Flood maps, surge models, heat records—events kept showing up outside the envelope we built systems around.”

What comes next: adaptation and emissions cuts

Scientists involved in the attribution study say events like this underscore two parallel imperatives: cutting the greenhouse gas emissions that drive long-term warming and adapting more quickly to the extremes that are already locked in.

That includes developing and funding heat action plans that trigger early warnings, opening cooling centers when thresholds are crossed, reaching out to isolated residents, and updating labor rules to better protect outdoor and non-air-conditioned indoor workers. Urban planners and city officials are also examining measures such as expanding tree canopy, using more reflective building materials and rethinking building codes and land use in chronically hot neighborhoods.

The March heat dome, experts say, offers a preview of the kind of conditions that will become more common if global temperatures continue to rise.

As the sun dipped behind Phoenix’s skyline that week, evening temperatures still hovered in the 90s. Fans streamed into a rescheduled night baseball game, clutching cold drinks. A few blocks away, trailheads that typically would have been busy on a mild spring afternoon sat quiet behind barricades.

For many, the memory of blizzard headlines from just days earlier already felt distant. The calendar still said March, but the air outside suggested a different season—one that scientists say will reach deeper into the year as the climate warms.