Extraordinary October heat wave scorches the west through the weekend

Heat warnings have been extended into the weekend around San Francisco and early next week for parts of Los Angeles southward to the east of San Diego.

It comes after hundreds of records fell again Thursday, with similar expected each day through the weekend.

During this heat wave, many locations in the Bay Area have witnessed their hottest days of the summer season. San Francisco reached 94, while Oakland made it to 97 and Napa hit 106. Thursday featured extensive all-time highs for October in the Central Valley.

Phoenix set yet another record high Thursday, moving to 10 daily record highs in a row. It is an unprecedented run of heat records for the city and is approaching a record for any American city.

Exacerbated fire risks are also ongoing — new starts were reported in Southern California Thursday. Red-flag warnings for the greatest fire danger cover a large swath, generally on the north end of the hottest weather at present, running from northern California through the north-central Rockies and out to the Plains of Wyoming and South Dakota.

Hundreds of high temperature and warm low temperature records have been set daily to start October — a continuation of a trend that started the last week of September. Around 2,000 daily warmth records have been set over the past 10 days in the western United States.

Among the daily records, at least 230 October records for highs have been set in the opening days of the month. Numerous are at stations with about, or more than, 100 years of data.

Among the longest-term stations, all-time October highs include:

• 117 in Palm Springs — tied all-time U.S. high for October
• 114 in Death Valley
• 113 in Phoenix
• 112 in Needles, Calif.
• 107 in Los Angeles’s Van Nuys neighborhood
• 106 in San Jose
• 105 in Tucson
• 104 in Modesto, Calif.
• 103 in Sacramento
• 89 in Grand Junction, Colo.
• 85 in Cheyenne, Wyo.

Additional warmth records will come in buckets through the weekend before easing to start next week.

That has been the story of 2024 in the region, and, in many cases, 2023. Human-caused climate change and remnant effects from last winter’s El Niño climate pattern are primarily to blame for the persistently toasty temperatures.

Record highs of 100 to 110 are anticipated daily in interior central and Southern California, southern Nevada and Arizona into at least Monday. Desert areas see it the worst and for the longest, but records may extent into the central United States at times, where readings will rise to the 80s and 90s many spots.

“Temperatures reaching 110 this late in the year is pretty unfathomable at this point, given the lowering sun angle, length of day, and considering the previous latest 110+ on record for Phoenix was Sep 19, 2 weeks ago,” the Weather Service office there wrote.

The lengthiest streak of record highs in the United States as of last year was in Burlington, Iowa, during the 1930s, where 14 record highs in a row were observed, according to Alaska climatologist Brian Brettschneider.

Including Friday, Phoenix is forecast to pick up between four and six more record highs in a row, which would put this run at 14 to 16 straight days.

Temperatures fall off to around 5 to 10 degrees above average in about a week for most of the scorched region, which is substantially down from the widespread 15 to 20 above through the weekend. Even cooler along the coast, where a marine air mass will influence temperatures.

At 131 days 100 or above this year in Phoenix, cooler hopes may be building. Temperatures dipping to the 90s could cap the annual total around 140 or just shy of the record 145 for a year. The final 100-degree day there averages during the first week of October, per the last 30 years of climate data.

While it may not stay absurdly hot, it will remain above average through at least mid-month in most of the western United States. With time, the highest temperatures relative to normal may continue to shift eastward across the country.