Heat wave in western US could trigger sweltering summer

A major early-season heat wave heading toward western North America threatens to produce sweltering temperatures that could break records. Here, a jet plane flies over Phoenix during extreme heat in July 2023.

(Matt York/Associated Press)

A major early-season heat wave heading toward western North America threatens to produce sweltering temperatures that could break records, prime the landscape for wildfires and spark a scorching summer.

A powerful ridge of high pressure, or thermal dome, will bring unusually warm temperatures to the Golden State by the middle of this week before spreading to the Pacific Northwest and southwest Canada, according to Daniel Swain, climatologist at UCLA. Temperatures could remain well above normal across much of the region for 10 to 14 days.

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The hottest areas of California will not be the inland desert regions that typically see high temperatures, but rather parts of Northern California and the Sierra Nevada foothills, Swain said during a press briefing Friday. The Sacramento Valley could see widespread triple-digit temperatures, including over 110 degrees in the central and northern valley by Wednesday and Thursday, up to 20 degrees above normal.

“This will be another event in which a good portion of California’s population – residents near the coasts of the Bay Area and Southern California – are unlikely to experience extreme heat,” Swain said. “But you may not have to go that far inland to see significantly higher temperatures, and if you go far inland enough, you might even see record heat .”

Far Northern California will likely experience its first 100-degree day of the year by Wednesday, according to the National Weather Service. The Central Valley is under an excessive heat watch, with a risk of soaring up to 110 degrees in the San Joaquin Valley.

The event bears some similarity to a record heat dome that smothered the Pacific Northwest for 27 days in June and July 2021, although it will be smaller in magnitude, Swain said. This event resulted in numerous studies and research papers and was associated with hundreds of deaths, massive die-offs of marine life, crop losses and damage to infrastructure.

The 2021 heat dome also intensified the 2021 fire season – a pattern that could repeat itself this year.

Although California has experienced two relatively quiet fire seasons thanks to back-to-back wet winters, it has seen an explosion of new vegetation that can be healed by incoming heat, creating fuel for future flames. The state has already seen several small fires, including a 1,300-acre fire in Santa Barbara County.

“There is no real indication of extreme fire risk with this pattern, but it will pave the way for vegetation to dry out more quickly in June after a few wet winters, and could potentially accelerate fire conditions forest later in the season,” Swain said.

Incoming warmth could also spell doom for the rest of the state’s snowpack, which is down to about 44% of normal for this time of year after peaking in April. The melt won’t trigger flooding, but could cause high, cold river flows — a potential danger for swimmers seeking relief from high temperatures, according to the weather service.

Although the worst effects of the heat wave could dissipate by mid-June, it could also mark the start of a long, hot summer, forecasters say.

The latest seasonal temperature forecasts from the National Oceanic and Atmospheric Administration indicate that June, July and August will bring above-normal temperatures to almost all of the United States, with the highest likelihood of warmer-than-usual conditions in the four corners region of Arizona. , New Mexico, Colorado and Utah.

NOAA’s latest seasonal forecast indicates a high chance of warmer-than-normal temperatures across most of the United States in June, July and August.

(The National Oceanic and Atmospheric Administration)

In California, the odds favor above-normal temperatures across the state, with a higher probability further inland.

Last year, Arizona made headlines when Phoenix suffered a record 31-day streak of temperatures of 110 degrees or higher. In Death Valley, the mercury soared to 128 degrees, an all-time world record.

Dan Collins, a meteorologist at NOAA’s Climate Prediction Center and author of the latest seasonal forecast, said the simmering summer will be heavily influenced by changes in the El Niño-La Niña cycle, as well as climate change.

“This seasonal outlook depends largely on these two factors,” he said.

El Niño, a tropical Pacific weather phenomenon, has been responsible for record temperatures around the world since its arrival last year. April marked the 11th consecutive month of record global temperatures, and 2023 was the hottest year on record on the planet.

Even though El Niño has weakened, it still influenced boiling tropical ocean temperatures that drive atmospheric circulation patterns, including the coming heat wave, Collins said.

But part of the reason the West is expected to experience an abnormally warm season is climate change, which has driven an overall warming trend in the region in recent decades.

“El Niño may have contributed to warming global temperatures, but of course there was also a long-term temperature trend,” Collins said.

The upcoming heat wave won’t be the first notable heat event this year either. Several Florida cities have broken daily records in recent weeks, including 97 degrees in Tampa and Orlando, and 96 degrees in Miami and West Palm Beach. Heat indices – measures including temperature and humidity – were several degrees higher.

Heat also sweltered parts of the Caribbean, Central America and Mexico, where temperatures in Oaxaca reached a record 118.4 degrees on May 26. Parts of Mexico are also experiencing extreme drought, with authorities warning that Mexico City will soon run out of water.

Extreme heat is one of the deadliest effects of climate change, and heat in Mexico has already been linked to more than 60 deaths this year. Last year’s Phoenix heat wave killed at least 645 people, while the 2021 Pacific Northwest heat wave is estimated to have contributed to at least 600 deaths, many of them in households without air conditioning.

Collins said the impending heat wave has the potential to not only produce record daytime temperatures, but also record nighttime temperatures.

“It’s not just summer that’s coming as expected,” he said. “This is an extreme event that is predicted.”

Swain, of UCLA, said there is still uncertainty about the heat wave’s impact on the western United States, in part because it could persist until mid- June. But what is clear is that it is going to be particularly hot for millions of people.

“These are pretty darn hot temperatures,” he said. “These are significant numbers.”