September's heat wave in the West is the most severe on record

July 2024 · 6 minute read

The heat wave that’s been gripping California and other parts of the West for 10 days and counting is the most severe ever recorded in September, weather experts have said — confirming what California’s governor is calling the “hottest and longest on record” for the month.

The data supporting the assertion is overwhelming. Records began falling on Aug. 30 when Seattle and Portland set calendar day records of 90 and 100. And it’s not yet over — while the region’s heat wave peaked on Tuesday, it’s expected to continue until Saturday, ending after a total of 12 days.

In just the past week, nearly 1,000 heat records have been broken, including more than 270 monthly records. Some places, like Salt Lake City, Sacramento and Reno, Nev., have broken their September records multiple times and by large margins.

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Sacramento and San Jose, where it reached 116 and 109 degrees on Tuesday, clinched all-time records — meaning their temperatures exceeded levels observed on any previous day or month.

It’s the “greatest September heat wave ever west of the Rockies hands down,” tweeted weather historian Maximiliano Herrera on Wednesday.

Driest, wettest, hottest: Sacramento’s troubling trifecta of extremes

In addition to its magnitude and duration, the heat wave has also been exceptional for its scope. Record-shattering temperatures have stretched from Arizona to Washington state and as far east as North Dakota.

At least two states have posted their highest temperatures ever observed during September:

When Death Valley soared to 125 degrees Tuesday, it fell just one degree shy of the September California and world records.

As northern California experiences one of its longest and hottest heat wave to date, residents struggle to stay cool amidst record-breaking temperatures. (Video: Alice Li/The Washington Post)

Of all the states, California has seen the most extreme temperatures for the longest period of time. Sacramento, Death Valley, Stockton and Fresno all saw their warmest 7-day periods in September “by far” according to an analysis by weather enthusiast Don Sutherland.

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At the heat wave’s peak on Tuesday, California Gov. Gavin Newsom (D) called it “unprecedented,” tweeting that it “will be the hottest and longest on record for September.”

Experts concurred.

“This will be essentially the worst September heat wave on record, certainly in Northern California and arguably for the state overall,” said Daniel Swain, a climate scientist at UCLA, in a live discussion on Twitter.

Christopher Burt, author of a book on weather extremes, called Tuesday “one of the, if not the, hottest single day in California’s observed weather history.” That day, California’s power demand spiked to an all-time high.

California scrambles to avoid blackouts as it pursues a green energy future

Although the heat wave is slowly easing, it is still setting records. The National Weather Service projects about a dozen more will be broken or tied through Saturday. Excessive heat warnings and heat advisories are still in place for about 30 million people in California.

This is exactly the kind of heat wave that is expected to become more common because of human-caused climate change, which has already made such events more intense, frequent and prolonged.

Rundown of key records

Below we list some of the most significant heat records set since the heat wave began:

Unprecedented September heat shattered daily records in Reno, NV this week. Tuesday, Sept 2, 2022 observed a high of 106°F, breaking the previous daily record by 10 degrees and becoming the 2nd highest temperature ever recorded at KRNO. #nvwx pic.twitter.com/1WxAXvNPT9

— NWS Reno (@NWSReno) September 8, 2022

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