'Exceptionally dangerous' heat wave could broil California for several days

Excessive Heat Warnings so far cover 15 million in California with Excessive Heat Watches posted in western Oregon and western Nevada with widespread areas of major to extreme heat risk.

SACRAMENTO, Calif. — An intense and potentially record-setting ridge of high pressure is building across California and the West, threatening days and perhaps more than a week of a dangerous, life-threatening heat wave.

The worst of the heat will be centered in California’s Central Valley, where as many as 10 days or more of 110-degree heat looms. But just about all of California, stretching into western Oregon and western Nevada, will swelter for an extended period.

So far, Excessive Heat Warnings cover 33 million in California into western Oregon, western Nevada and Arizona. There are widespread areas of major to extreme heat risk.


But it’s not just the near or record-breaking readings on the thermometer that have forecasters worried, but their duration, as the hot pattern remains stuck in place.

"The record-breaking heat isn’t going anywhere," forecasters with the National Weather Service in San Francisco wrote in their forecast discussion Tuesday morning. "The high-pressure dome will linger over California for at least a week, with more long-range guidance suggesting that timeline may even be optimistic."

The San Francisco Bay Area has the possibility of recording its all-time hottest temperature at 5,000 feet this week (currently 88 degrees) among their twice-daily weather balloon launches, and is likely to remain in the 98th percentile for heat for at least six days, and possibly as long as 12 days, NWS forecasters said.

"While we have all seen temperatures like this before, this event may end up approaching the upper end of what we’ve seen historically, in terms of longevity," NWS San Francisco said.

In their Excessive Heat Warning, they were even more dire.

"Several days of temperatures well above normal will lead to compounding effects among people and infrastructure, with the possibility of numerous heat related fatalities. It cannot be stressed enough that while one day at these temperatures may be manageable for some, an event of this scale, magnitude, and longevity will likely rival anything we've seen in the last 18 years. Heat is the number one weather related killer in the United States. By this weekend, it is VERY LIKELY that we add to that statistic if preparations are not taken seriously."

Similar warnings were shared by forecasters across the region.


"This is a severe heat event," said NWS forecasters in the San Joaquin Valley.  "The heat risk index is in the major to extreme category through the end of the forecast period. There is not a reason to disbelieve the guidance."

"Widespread Major to Extreme Heat Risk will last at least into the weekend," echoed the NWS in Sacramento.

"For Hoopa in particular, this could easily approach the all-time high temperature record of 111," said the NWS in Eureka. "All indicator(s) point to strongly above average temperatures being here to stay for the foreseeable future."

Medford, Oregon, could challenge or exceed its record of 10 consecutive days over 100 degrees with the potential of reaching 110 degrees over the weekend.


Even Death Valley could reach well into the mid-upper 120s. If temperatures warm to near 130, they would be among the hottest temperatures ever reliably recorded on Earth.

Even more concerning is the lack of cooling overnight, with many areas only dropping into the 70s to low 80s, allowing minimal heat recovery time.

As mentioned, the long-range forecasts do not give a clear indication of when the heat wave will end. Even if temperatures come off their peaks next week, long-range indications are highly confident that above-average temperatures will remain in the West.