California's October heat wave is finally easing

After nearly a week of record-breaking temperatures, Californians should feel some relief from the oppressive October heat wave that has ravaged inland areas — and even some coastal regions — across the state.

A cooling trend is forecast to begin Tuesday and continue through the rest of the week as the relentless ridge of high pressure that has formed over the southwestern U.S. begins to shift eastward.

“There is a light at the end of the tunnel,” the National Weather Service in the Bay Area wrote on X on Monday, with most heat warnings across the state set to expire Tuesday morning.

That doesn't mean temperatures will immediately drop to a fall-like chill, but thermometers across the state are expected to slowly fall from their unseasonable highs, which in many areas were 20 degrees above average for this time of year.

“We can expect the above-average temperatures to definitely continue for at least the next week, but not the record-breaking heat that we've seen,” said Kyle Wheeler, a meteorologist with the National Weather Service in San Diego. “By the end of the week and weekend it will definitely feel like fall – relatively speaking.”

Until this cooling trend begins, inland communities across the state will continue to experience significant heat through Monday night – with excessive heat warnings still warning of triple-digit highs – before gradual cooling begins. Wheeler said most areas are expected to fall closer to seasonal averages by the weekend.

The recent heat wave showed “a big divide” between coastal areas and inland valleys, deserts and mountains, particularly in Southern California, said Rose Schoenfeld, a meteorologist with the National Weather Service in Oxnard. Much of the Los Angeles, Orange and San Diego County coastlines did not experience the effects of this heat wave due to a heavy marine layer.

But it was definitely humid in inland California.

On Sunday, Indio set the state's highest temperature for the final calendar day at 116 degrees. According to the National Weather Service, this high, which was also reached in Ocotillo Wells, was the hottest temperature in the contiguous United States.

Throughout the hot weekend, temperature records were broken from Ukiah to Ramona and virtually everywhere in between, including the Antelope Valley, the Southeast Desert and the Bay Area. In the Central Valley, Fresno, Merced, Hanford and Madera all hit all-time highs for the month of October last week, reaching 105 or 106 degrees on Oct. 3.

Las Vegas has already reached 100 degrees or higher for six days in October – every day so far – which meteorologists say is a rare occurrence throughout the month.

The excessive heat that persisted for days was the result of what officials described as an unusual pattern of continuous high pressure – rare for this time of year, but not unheard of.

“These unusually strong ridge or trough patterns are going to form in different parts of the world and we happen to be right under them here,” Wheeler said.

Since there were no other systems to intervene, such as an incoming low-pressure system, Schoenfeld said the ridge of the high-pressure system was simply over the Southwest. High-pressure systems in the upper atmosphere typically drive all of California's major heat waves, forming a lid over an area where the air is sinking – a phenomenon sometimes called a heat dome – that prevents hot air from rising and leaving it in the Essentially captures. High pressure systems also suppress cloud formation, allowing more direct sunlight.

“There was just nothing significant to bring it down,” she said.

But even as the most extreme temperatures drop, Schoenfeld said California will remain in a “stagnantly warm weather pattern.” The Climate Predication Center shows a high probability that the Golden State — and the entire western U.S. — will experience above-average temperatures through the end of October.