By Andrew Freedman, CNN
(CNN) — Meteorologists are reaching for superlatives to describe an oncoming heat wave so intense and rare for this time of year that it could leave some locations shattering their all-time temperature records for April before that month has even begun.
This extreme event, made far worse by human-caused climate change, will bring summerlike temperatures during March to locations from California to Texas, northward all the way to Montana. Extreme heat warnings and other heat alerts are in effect for millions from San Francisco to Phoenix and are likely to expand with time.
The event is just getting underway. Before it ends later next week, it will have scorched nearly the entire Western part of the country and parts of the Plains states, toppling dozens of daily and monthly temperature records by unusually large margins.
In Phoenix, for example, the all-time March high temperature record is 100 degrees, but during this heat wave the temperature is forecast to climb to at least 106 degrees and remain above the century mark for multiple days.
“Many locations are likely to set both all-time high temperatures for the month of March and their earliest 100-degree temperature on record,” the National Weather Service stated, predicting high temperatures of up to 30 degrees above average for this time of year.
This extreme heat event may be comparable in its intensity and rarity to the 2021 Pacific Northwest heat wave, which killed hundreds and sent temperatures soaring into the 120s Fahrenheit in Oregon and Washington State during June. Temperatures won’t be nearly that hot over the next two weeks (it is still March, after all) but both events stemmed from the same place: record-strong heat domes parked over a particular region of the country for extended periods of time — plus a healthy dose of climate change.
A heat dome is a sprawling and strong area of high pressure extending thousands of feet into the atmosphere. That pressure pushes down on the air underneath it, compressing and heating it. This also squelches any storm activity, and heat domes can act like detour signs in the atmosphere, rerouting storms around them. This one is likely to set records for its strength relative to the time of year and could even rival or beat previous intense heat domes that existed during the summer months, such as the 2021 event.
Its intensity is important because meteorologists use such measurements, in addition to surface temperatures, to compare heat waves throughout history and conduct studies of climate change’s influence.
Studies showed that 2021 heat wave would have been virtually impossible in the absence of climate change from the burning of fossil fuels. As the planet warms, studies have repeatedly shown that heat waves are becoming more likely, longer lasting and more severe. Since that earlier extreme heat event, multiple heat waves elsewhere in the world have been found to be possible only with the human contribution of planet-warming pollution.
Russ Schumacher, a meteorologist and Colorado’s state climatologist, called the heat dome “astonishing” for its intensity in March. Other meteorologists have described the strength of the heat dome as “genuinely startling” and “mind-boggling” via social media.
“With warming, you expect the warm conditions to be more likely and happen more frequently,” Schumacher said. “When you get a heat wave, you expect it to be warmer or lasting longer.”
“But it also just takes a really unusual weather pattern to set something like this up, and that’s what we’re going to be seeing this week, as well,” he said.
The heat wave also constitutes a significant public health threat.
Extreme heat is typically the number one weather-related killer in the US each year, and an early season heat wave poses especially acute public health dangers since western residents won’t yet be accustomed to temperatures in the upper 80s to low 100s, depending on the location. Compounding the threat is the lack of air conditioning in parts of the affected regions.
The health threat is multifaceted, too. During the summer months, people can escape to rivers and lakes for relief, but because it is only March, hypothermia is a serious risk for anyone venturing into the water to try to cool down.
The early heat could reverberate for months and have other deadly consequences, including causing the region’s already low snowpack to melt out at least a month ahead of schedule. This raises water supply concerns and wildfire worries for the upcoming dry season.
The West entered this heat wave on the heels of its hottest winter on record. Colorado had its thinnest snowpack since 1981, according to Schumacher. “March is when typically we would be seeing more snow storms and continuing to build up that snowpack in the mountains,” he said. “And it looks like we’re going to be going in completely the opposite direction this week.”
In California’s Sierra Nevada Mountains, where snowfall was closer to average this winter, the heat wave will cause the remaining snowpack to rapidly vanish, perhaps completely, about five weeks earlier than normal.
Schumacher said understanding why this winter was so warm in the West, as well as studying the heat wave, is crucial to better anticipating what’s ahead in the West. “These kinds of warm months and seasons are probably going to become more likely with future warming,” he said.
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