Temperatures surpassing 100 to 120 will be a daily occurrence over most of the state, while warm nighttime lows offer minimal relief. A powerful and abnormally persistent heat dome will kill off clouds and also keep cooler fog at bay. The heat will also fuel an escalating fire threat; already, the Thompson Fire in Northern California has grown to over 3,000 acres and destroyed structures.
The dangerous heat is projected as far into the future as reliable forecasts are available. All-time records approaching 120 may be threatened as far north as Redding, while Death Valley could approach 130 degrees, which is the highest temperature reliably measured on the planet.
The Weather Service has warned that “numerous heat related fatalities and rolling blackouts” are possible.
The heat wave comes amid the hottest year on record so far for the planet. The last 13 months, including June, have set record highs. According to the science communications firm Climate Central, human-caused climate change has made this week’s heat wave in California at least five times as probable.
The maps that follow help illustrate the seriousness of the heat that lies ahead.
Heat warnings cover 70 percent of the state
More than 70 percent of California is under an excessive-heat warning. Some of the heat alerts issued by the Weather Service extend seven days into the future, which is an unprecedented duration, according to the San Francisco Chronicle.
Cities under excessive-heat warnings include Redding, Sacramento, Fresno, Bakersfield, Santa Barbara, Burbank and Palm Springs.
Heat advisories — for slightly less extreme conditions — are in place for Los Angeles, Santa Maria, San Francisco and other near-coastal cities along with portions of the Sierra Nevada. A few spots right at the coast are not included in any alerts.
Temperatures could climb above 130 degrees
The numbers are startling: Large portions of California will experience highs above 110 degrees over the next week. Some areas will surpass 120. Only areas at the immediate coast and in the higher mountain peaks will escape the triple digits.
Death Valley, which holds the record for the hottest temperature ever measured on the planet, has forecast highs of 126, 128, 130, 131, 131 and 133 over the next six days. Its world-record high temperature of 134 was set in 1913, although there are questions about the reliability of that measurement. In 2020 and 2021, it reached 130 degrees, the highest reliably observed temperature in modern records. Last summer, it hit 129.
Heat dome to near historic intensity
The heat dome responsible for these extreme temperatures is forecast to climb to near record strength and remain parked over California and the southwestern United States for seven to 10 days.
“This is the hottest synoptic pattern that we see,” wrote the Weather Service office in Las Vegas, where all-time highs may be reached.
The heat will not be confined to California but will also affect much of the Southwest and at times swell into the Pacific Northwest as well.
Studies have found that heat domes such as this are becoming larger and more intense because of human-caused climate change.
A torrent of record highs and warm lows is projected by the Weather Service. Hundreds of records will probably fall before the heat wave ends.
Calendar-day records will be most common, but some monthly and even all-time marks may be threatened. The number of records set will increase through Thursday and become most numerous between Friday and early next week.
Some of the all-time records in jeopardy include 121 in Palm Springs on Saturday, 118 in Redding on Saturday and 118 in Las Vegas on Monday.
Extreme heat could persist for 7 days
The federal government’s 0 to 4 HeatRisk index is predicted to reach Levels 3 and 4 — considered major and extreme — every day for at least the next week in the Central Valley and deserts.
At these levels, the risk of heat-related illnesses increases substantially, particularly for vulnerable groups such as outdoor workers, the homeless and older adults.
While major coastal cities will be mostly spared, areas just inland will experience multiple days of dangerous heat.
Jason Samenow contributed to this report.
