March Heat Dome Shatters Records in the West, Strains Water Supplies and Sends Hundreds to Medics

On a Saturday in late March, crowds poured into the Luke Days airshow at Luke Air Force Base outside Phoenix in T-shirts and ballcaps, expecting spring sunshine and fighter jet flyovers. By midafternoon, paramedics were racing stretchers through the baking tarmac as temperatures surged past 100 degrees. More than 400 people were treated for heat-related illness over the weekend and about 25 were taken to hospitals, base officials said.

A few hundred miles to the northwest, ski patrollers in Colorado were roping off slushy runs and posting early closing dates. In the California desert, thermometers climbed to 112 degrees — the hottest March reading ever measured in the United States.

Over roughly a week in mid- to late March, a powerful “heat dome” parked over the western United States and pushed summerlike temperatures into what is still technically winter. The event shattered hundreds of daily records and more than 160 all-time March highs from California to the central Plains, toppled the national March temperature record by four degrees and triggered rapid snowmelt across a region that depends on mountain snow for its water supply.

Climate scientists say such an event would have been virtually impossible in a preindustrial climate, and that human-caused warming added several degrees to the extremes that baked the West.

A heatwave more typical of July than March

The heat built quickly after March 16 as an unusually strong, nearly stationary high-pressure ridge settled over the West. The system, sometimes called a heat dome, acted like a lid in the atmosphere, forcing air to sink, clear skies to persist and temperatures to climb 20 to 35 degrees above normal in some areas.

By March 18, downtown Los Angeles had hit 95 degrees, breaking its all-time March record. Las Vegas climbed to 94. Phoenix registered multiple days above 100, setting a new March record near 103 degrees at Sky Harbor International Airport and recording one of its earliest triple-digit streaks on record.

In the desert along the California-Arizona border, where March highs typically top out in the 80s or low 90s, temperatures surged into uncharted territory. On March 20, thermometers at Buttercup and Squaw Lake in southeastern California and at sites in the Yuma Desert in southwestern Arizona reached 112 degrees, according to federal climate data. Those readings surpassed the previous U.S. March temperature record of 108 degrees, set in South Texas in 1954 and tied in 2020.

“It’s extremely unusual to see this kind of widespread, record-breaking heat in March,” said Gregg Gallina, a meteorologist with the National Weather Service. “Basically the entire U.S. is going to be hot. The area of record temperatures is extremely large.”

The heat did not stay confined to the Southwest. As the ridge bulged eastward around March 20 to 24, temperatures in Denver reached 87 degrees and Grand Junction hit 88, both March records. Kansas City and North Platte, Nebraska, touched 92, also all-time March highs.

Snowpack melts weeks early

The timing of the heat proved as significant as the numbers on the thermometer. Western states enter spring heavily reliant on mountain snowpack, which normally builds through late winter and melts gradually into rivers and reservoirs from April through June.

That pattern had already been strained. The winter of 2025-26 was among the warmest on record across much of the West, and snow surveys in early March showed most basins running below normal. By March 9, roughly nine in 10 snow monitoring stations in the region were reporting snow water levels below the historical median.

When the heat dome arrived, it accelerated melt at all elevations.

In Colorado, the state’s climate office reported that snow was disappearing from high peaks and low hillsides alike, and warned that statewide snowpack was likely at or near the worst levels ever recorded for late March. Between March 18 and March 27, Colorado’s average snow water equivalent dropped from around 57% of normal to close to 30%, according to state and federal data.

Overnight freezes, which help lock snow in place, became weak or disappeared entirely at many elevations, the Colorado Avalanche Information Center said. That combination of warmth and unstable snowpack increased avalanche risk and shortened the window for safe backcountry travel.

On the ground, ski areas including Ski Cooper, Sunlight Mountain Resort and Howelsen Hill closed weeks earlier than planned, citing thin bases and the prolonged heat.

Farther west, researchers at the University of Nevada, Reno, said record March heat — including a 106-degree reading in Laughlin that set a new statewide March high — wiped out much of the lower-elevation snowpack in the eastern Sierra Nevada and Great Basin in a matter of days. They described one of the largest single-day melt events ever recorded in the eastern Sierra, second only to an episode associated with major flooding in 1997.

That water is now rushing into rivers and reservoirs such as Blue Mesa in Colorado and Lake Mead and Lake Powell on the Colorado River system. Many of those reservoirs remain well below capacity after years of drought and heavy use.

“Early and rapid snowmelt boosts streamflows in the short term but can worsen shortages later in the summer,” said Becky Bolinger, assistant state climatologist in Colorado. “We rely on having that slow-release reservoir of snow into June and July, when demand is highest.”

The Colorado River, which supplies water to about 40 million people and millions of acres of farmland in seven U.S. states and Mexico, is at the center of ongoing negotiations over long-term cuts in use. Water managers say this year’s heat-driven melt reinforces concerns about how a warming climate is changing the basic assumptions behind Western water law and planning.

Fire season and fields pushed ahead

Even with snow still on some peaks, conditions at lower elevations resembled late spring.

The National Weather Service issued Red Flag Warnings and fire weather watches across parts of Texas, New Mexico, Oklahoma, Colorado and Nebraska as hot, dry air and gusty winds swept across cured grasses and rangelands. In Nebraska, the heat arrived on the heels of large grass fires — including the Morrill and Cottonwood fires — that had already burned more than 1,200 square miles, according to state officials.

In the central Plains, the record March warmth sped up budding in trees and emerging crops. Farmers and nursery operators around Kansas City and eastern Kansas expressed concern that any return to freezing temperatures, which are still common in early April, could severely damage fruit trees, winter wheat and ornamentals that broke dormancy early.

Many of those same areas remain in drought. Federal drought monitors in late March showed more than half of major U.S. winter wheat and sorghum acreage experiencing some level of dryness, meaning the heat compounded existing soil-moisture deficits.

Health systems respond to “off-season” heat

Public health agencies in the Southwest say the March heatwave underscored how extreme heat is no longer confined to July and August.

At Luke Air Force Base in Glendale, near Phoenix, officials said most of the people treated for heat-related illness during the Luke Days airshow were children under 12 and adults over 60. Many had pre-existing medical conditions such as heart problems. Organizers ended up closing the gates early on Sunday because of the heat.

The American Red Cross issued national guidance on staying safe in hot weather as records spread into the Plains and toward the East Coast. In Maricopa County, which includes Phoenix and has recorded some of the nation’s highest heat-related death tolls in recent years, health officials rolled out their 2026 heat response plan the same week the heat dome peaked.

The plan calls for expanded cooling and respite centers, outreach to unsheltered residents and enforcement of local rules that require landlords to keep indoor temperatures below certain thresholds. Phoenix requires air-conditioned rental units to be capable of maintaining 82 degrees or lower.

Health data from recent summers in the county show older adults, people with chronic illnesses, low-income renters without reliable cooling and people experiencing homelessness are disproportionately likely to die during extreme heat.

“An event like this in March catches people off guard,” said Nick Staub, who coordinates heat programs for Maricopa County’s public health department. “Events, schools, outdoor work — they’re often not planning for triple digits this early in the year.”

A clear climate signal

Within days of the heatwave, an international group of scientists with the World Weather Attribution initiative released a rapid analysis of the event. Using weather observations and climate models, they compared the likelihood and intensity of such a heatwave in today’s climate with a world that had not warmed due to human greenhouse gas emissions.

Their conclusion: record-shattering March temperatures across western North America would have been “virtually impossible” without climate change. The team estimated that in the current climate, with global temperatures about 1.3 degrees Celsius above preindustrial levels, a March heatwave of this magnitude has a statistical return period on the order of 500 years — still rare, but now within the realm of possibility.

The researchers also found that human-caused warming added roughly 2.6 to 4 degrees Celsius — 4.7 to 7.2 degrees Fahrenheit — to the peak temperatures during the event.

A separate analysis by the nonprofit research group Climate Central used its Climate Shift Index to quantify the influence of climate change on the daily temperatures experienced during the heatwave. Many locations across the West registered CSI values of 3 to 5, meaning climate change made those particular hot days three to five times more likely or more.

Scientists who study extreme events say the March heat dome fits into a broader pattern: more frequent and intense heatwaves, including outside the traditional summer season, and changes in the behavior of high-pressure ridges and atmospheric “blocking” systems that can lock in long-lived extremes.

Seasons under pressure

For residents of the West, those changes are beginning to show up in everyday decisions — from when to schedule an airshow or a marathon to how long a ski season can be expected to last.

City officials in Phoenix and other Sun Belt metros are considering whether to move up the formal start of “heat season” for emergency planning. Fire managers are weighing how to staff earlier in the year as grasses cure faster and snow retreats from higher elevations. Water negotiators along the Colorado River are confronting what early, repeated heatwaves mean for long-term reservoir operations.

The March 2026 heat dome arrived just as winter was ending. It set a new national record for March, stripped snow from mountains weeks ahead of schedule and sent hundreds of people to medical tents who thought they were spending a mild spring day outdoors.

At roughly 1.3 degrees of global warming, scientists say, such extremes remain unusual. But as the world continues to warm, they expect events like this one to become less like anomalies — and more like previews of the conditions communities will need to plan for, even before summer officially begins.