Historic, unforgiving Western heat wave is peaking and crushing records

WEATHER NEWS: Historic, unforgiving Western heat wave is peaking and crushing records


A historically severe September heat wave is baking the West, breaking hundreds of records, posing a danger to public health and pushing California’s power grid to the limit. Some records have been shattered by wide margins as the scorching air mass exacerbates the fire danger in the drought-stricken region.

California’s Independent System Operator (ISO) says the state’s electric grid is under heavy strain and warned consumers “to be prepared for possible outages” Tuesday evening.

“As the state faces the hottest day in this prolonged, record-breaking heat wave, grid conditions are expected to worsen,” the grid operator wrote in a news release. “If needed, ISO could order utilities to begin rotating power outages to maintain stability of the electric grid.”

The agency, which declared an energy emergency alert, is predicting an all-time historic high demand of 52,258 megawatts Tuesday afternoon, surpassing its previous record of 50,270 megawatts on July 24, 2004.

The ISO urged residents to “precool” their homes to 72 degrees Tuesday and Wednesday mornings, and then turning the thermostat to 78 degrees during peak demand hours between 5 and 9 p.m. It has called for such reductions on seven straight days.

During a news conference on the September heat wave, California Gov. Gavin Newsom (D) on Aug. 31 said “we’re living in an era of extremes.” (Video: The Washington Post)

The heat is historic for both its duration and intensity, evidenced by long-standing monthly and all-time records that continue to be toppled. San Jose, Calif. set an all-time high of 109 degrees Tuesday afternoon.

In Sacramento, the downtown district got to 113 degrees Monday, just a degree below an all-time record set on July 17, 1975, and four degrees hotter than the previous September record. Records there date back to 1877.

On Tuesday afternoon, Sacramento is expected to jump to 115 degrees, which would be both a monthly and all-time record as well as only the 11th time in the past 145 years that the city made it to 112 degrees or higher.

“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 Twitter Spaces discussion Tuesday. “By some metrics, it might be one of the worst heat waves on record period in any month, given its duration and its extreme magnitude, especially in Northern California and especially in the Sacramento region.”

A whopping 42 million Americans are under excessive heat warnings, including across most of California, northeast Arizona and adjacent southern Nevada. The Great Basin, southern Idaho and western Utah are under heat advisories.

“Extreme heat will significantly increase the potential for heat related illnesses, particularly for those working or participating in outdoor activities,” wrote the National Weather Service. “[There is a] very high risk of heat stress or illness for the entire population.”

The excessive heat is also fueling the risk for fast-moving fires.

Red flag warnings — connoting dangerous fire weather — encapsulate the entirety of Montana in addition to northern Idaho, much of Oregon and northern and eastern Washington.

California firefighters on Sept. 3 battled a fast-moving fire that erupted 230 miles north of Sacramento, injuring several people and prompting evacuation. (Video: Storyful)

A number of large wildfires have erupted over the last week in California, Oregon, Idaho and Montana. The fast-moving Mill Fire, which erupted Friday in Northern California, killed two people and injured three. On Monday, two people died and another was injured by the Fairview Fire, which started near the city of Hemet, which is about 75 miles southeast of Los Angeles in Riverside County.

Hottest weather yet possible for some on Tuesday

The heat will reach a blistering crescendo into Tuesday as a stagnant high pressure “heat dome” crests overhead. It’s been fending off clouds and rain and diverting the jet stream north into Canada. Beneath it, sinking air and unrelenting sunshine are delivering some of the hottest weather ever observed in the Golden State.

Outside of deserts, the worst of it has been focused in California’s Central Valley. The National Weather Service is explicitly forecasting Sacramento to reach an all-time record high of 115 degrees Tuesday. In addition to being an all-time record, that temperature would also obliterate what until Monday had been Sacramento’s monthly record for September of 109 degrees.

Some places in the Central Valley could approach 118 degrees.

“Still looking like the ongoing record-setting heat wave will peak today, but dangerous heat will likely persist through the end of the week,” wrote the Weather Service office in Sacramento on Tuesday.

The heat traces the spine of California down to the Bay Area and Southern California too. The San Francisco airport is expected to hit 99 degrees Tuesday. Although that is staggeringly hot, Sept. 6, 2020, was hotter by three degrees. Regardless, it’s still two dozen degrees hotter than the average of 75.

Los Angeles will spend the next few days in the mid to upper 80s, but should peak around 90 on Friday. Keep in mind that’s at the airport though — just a few miles inland, highs will hover around 100 to 105 degrees.

Death Valley, Calif., has hit 124 degrees three times in the past five days. It could flirt with 126 on Tuesday, which would tie a world record for September.

The heat has been spilling east too, bringing toasty weather to Denver, with record highs in the upper 90s to near 100 projected through Thursday. Salt Lake City — which has set a September record of 104 on Monday — will continue to hover in the low 100s.

The heat will begin to gradually ease Thursday. Temperatures closer to average will return to much of California over the weekend, although temperatures will remain somewhat above normal over the Pacific Northwest and Northern Rockies.

Around that time, moisture from Hurricane Kay in the Pacific southwest of the Baja Peninsula could begin wafting northward, lowering temperatures and possibly bringing some beneficial rainfall to Southern California and even farther north. However, its specific effects on the region are highly uncertain and it could also increase the potential for dry lightning that could increase the fire risk.

Climate change connection

While extreme heat events are not caused by climate change, human influence on our atmosphere is making them more frequent, intense, prolonged and, in some cases, larger. It propels already high-end events into record territory.

Breaking records by large margins, the heat wave bears shades of the unprecedented events that torched the Pacific Northwest in June of 2021 and Britain in July, both of which scientists concluded would have been virtually impossible without human-caused climate change.

Stateside, over the past week, more than 1,141 warm weather records have been set in the United States compared to just 36 cold records. If climate change wasn’t a factor, these extremes would roughly balance out.

From California to Montana, hundreds of heat records have been set since Aug. 30, and dozens more are in jeopardy over the coming days.

In addition to calendar day records, multiple locations have set monthly records and even all-time records (the warmest temperature observed in any month). We highlight some of the of most significant here:

  • San Jose, Calif. set an all-time record of 109 degrees Tuesday.
  • Salt Lake City has broken its previous September record high four times over the past week. It hit 105 on Tuesday, 104 on Monday, 103 Saturday and 102 Thursday. The previous monthly record was 100. It has hit at least 100 six times this month. Before 2022, it had only done so three times during September dating to 1928.
  • Grand Junction, Colo. set a September record high of 101 Tuesday.
  • Downtown Sacramento set a September record high of 113 Monday, just one degree shy of its all-time high of 114 from July 17, 1925. Stockton (112), Vacaville (115) and Marysville (113) also set September record highs in California’s Central Valley.
  • Fairfield, Calif., about 40 miles northeast of San Francisco, set an all-time high of 117 degrees Monday — three degrees above the previous record. Livermore set an all-time high of 116.
  • Reno, Nev., set a September record high of 104 on Sunday, after tying the previous monthly record of 102 on Friday.
  • San Diego tied its all-time warmest low temperature on record Sunday, falling to just 78 degrees.
  • Burbank, Calif., matched its all-time warmest low temperature on Sunday, only dropping to 82 degrees. On Wednesday, it set an August record high temperature of 112.
  • Las Vegas set a September record high minimum temperature of 87 on Sunday.
  • Casper, Wyo., set a September record high of 100 Sunday.
  • On Saturday, the low temperature in Death Valley of 102 degrees tied the highest minimum temperature ever recorded worldwide during September. Death Valley has topped 120 degrees on seven straight days, setting calendar day records of 123 on Wednesday, 124 on Thursday, 124 on Friday, 122 on Saturday, and 124 on Sunday. It has established a new September record for most days reaching at least 120.
  • On Saturday, many locations in the Mountain West set September record highs, including Great Falls (102), Bozeman (10o) and Butte (96) in Montana and Pocatello (102) and Idaho Falls (99) in Idaho.
  • The heat even surged into western Canada on Friday, where the village of Lytton set a September record for British Columbia of 103.3 degrees (39.6 Celsius).
  • Fresno, Calif. tied its September record high Friday, climbing to 111 degrees.
  • Redmond, Ore., set a September record high of 106 on Friday.

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