California fire
U.S. Army Soldiers from the California Army National Guard's Task Force Rattlesnake out of Redding, California, put out a fire Sept. 1, near Scott's Valley, California, during the CZU Lightning Complex Fire in Santa Cruz and San Mateo counties. (California National Guard / Flickr)

Temperatures reached ghastly levels in southern California and wildfire carved a path close to two of the state’s iconic national parks as a historic heat dome gripped the western United States during the traditional end-of-summer Labor Day weekend.

The heat had eased somewhat by Tuesday, September 8, but increasing winds were making the fire threat even worse across sun-baked landscapes from Washington to California.

“A potentially historic fire weather event is unfolding across the West, especially over the West Coast, during the next three days,” tweeted meteorologist Nick Nauslar (National Interagency Fire Center, or NIFC) on Monday.

Offshore wind season – the period in autumn when California’s most destructive fires tend to rage – is just getting under way. New research indicates that the state’s autumn fire season has gotten more dangerous in the past 30 years, and human-induced climate change may only accentuate this trend in decades to come.

Helicopter rescue tweet

As of Tuesday morning, California’s uncontained Creek Fire had torched more than 135,000 acres just northeast of Fresno, in between Yosemite and Kings Canyon national parks. More than 200 people were rescued by military helicopter from the fast-growing fire, which surrounded the Mammoth Pool Reservoir area late Saturday. At one point, people were advised to shelter in place and jump into the reservoir if necessary. Nearly 100 more people, mainly trapped hikers, were rescued by helicopter on Tuesday morning from the Lake Edison area.

The Creek Fire helped push 2020 ahead of 2018 for the most area burned by wildfire in modern California history, with roughly 2.1 million acres affected statewide as of Monday, according to Daniel Swain (UCLA/National Center for Atmospheric Research).

Parts of Southern California endured the hottest day in their history on Saturday. Temperatures hit 121°F at Woodland Hills – the first official reading of at least 120°F ever recorded in Los Angeles, Santa Barbara, Ventura, or San Luis Obispo counties. Likewise, a scorching 121°F at Chino was an all-time high for the vast Inland Empire region of San Bernardino and Riverside counties.

As noted by the New York Times, Southern California Edison reported that electricity use soared more than 8% above the previous daily record on both Saturday and Sunday.

Climate change is worsening California’s hellish wildfires

Well beyond California, extreme heat bathed much of the western U.S. underneath a powerful dome of high pressure that extended miles above the surface. A train of energetic impulses in the jet stream, boosted by powerful Typhoons Maysak and Haishen in the Northwest Pacific, helped pump up the western heat dome. As a whole, forecast models accurately predicted the dome’s intensification and the resulting extreme heat, although that was little comfort to those enduring the blast furnace.

One index of the heat’s intensity – the height of the 500-hectopascal surface, which is roughly the midpoint of the atmosphere and which rises as the lower atmosphere warms – set an all-time record in Medford, Oregon, on Sunday evening, reaching 6,030 meters, one of the highest such readings on record for the entire nation.

On the heat dome’s eastern fringe, the High Plains town of La Junta, Colorado, hit 108°F on Saturday, setting a state record high for any September. Denver reached 101°F, also a September record. About 60 miles northwest of Denver, the Cameron Peak Fire exploded to cover more than 102,000 acres by Tuesday morning, making it the state’s fifth-largest wildfire in modern records.

In some parts of the West, sun-blocking smoke provided an ironic trimming of the intensity of the record heat.

Blast of Canadian air a double-edged sword for western fires

By Tuesday morning, a shockingly strong cold front for early September was giving Colorado relief from the heat and parched conditions. Light snow was falling on Denver with a temperature of 33°F, less than a day after Monday’s high of 93°F – a case of severe weather whiplash.

The same front easing fire concerns in Colorado was aggravating them in the Pacific states. The upper-level impulse driving cold air across the Plains pushed strong, dry winds westward across the Rockies, generating gusts to 99 mph that knocked down trees in northern Utah. As the surge continues toward the Pacific coast from Washington to California through midweek, it will warm up and dry out – a classic recipe for autumn wildfire risk.

In central Washington, the Pearl Hill/Cold Springs fire complex tore more than 50 miles southward in less than 24 hours, by Monday night burning more than 180,000 acres. Meanwhile, some 80% of homes in the eastern Washington town of Malden were destroyed by the Babb Fire, according to the county sheriff.

Other fires erupted Monday night into Tuesday in and near the Cascades of western Washington and Oregon.

Satellite image of fires
As clouds and chilly air engulfed the central states, chimneys of smoke were being swept westward over the Pacific from wildfires in Oregon, Washington, and California at 1 p.m. EDT Tuesday, September 8. (Image credit: RAMMB/CIRA/Colorado State University)

Autumn fire risk is climbing as California warms

Although California’s average precipitation has held steady in recent decades, there’s trouble hidden in that reassuring-sounding statistic. The state famously lurches between wet and dry years, and temperatures are on the rise.

California has warmed close to 1 degree C (1.8°F) over the past 30 years, with most of that heating coming in late summer and early autumn. Even without any change in precipitation, long-term warming can increase fire risk by pulling more moisture out of parched landscapes. That’s especially true of California’s Mediterranean climate, where rains and mountain snows are concentrated from fall through spring and the summers are notoriously dry.

While many of the state’s largest fires occur in late summer, the deadliest and most destructive blazes tend to occur at the tail end of the dry season, from September to December. The most hazardous setups are when strong downslope/offshore winds (typically called Diablo winds in northern California and Santa Ana winds in southern California) arrive before the first heavy rains of autumn.

There’s now evidence that climate change is boosting the risk of extreme wildfire conditions in California autumns, according to an August study published in Environmental Research Letters and led by Michael Goss of Stanford University.

CA frequency of Autumn days
The average number of days each autumn in which the daily fire weather index exceeded the locally defined 95th percentile (i.e., the top 5% of days) more than doubled across California from 1979 to 2018. (Image credit: Fig. 3a, Goss et al., “Climate change is increasing the likelihood of extreme autumn wildfire conditions across California,” Environmental Research Letters 2020)

Examining weather data for the period from 1979 through 2018, Goss and colleagues found that the most extreme 5% of fire-weather days in autumn – as measured through an index based on temperature, humidity, winds, and precipitation – are now occurring more than twice as often as in the 1980s. In turn, these high-end days are closely associated with extreme autumn wildfires. The authors highlight two from November 2018: the Camp Fire, which decimated the town of Paradise in northern California, and the Woolsey Fire, which rampaged across parts of Los Angeles and Ventura counties.

When the authors carried out similar calculations for future climate, building on a much-used set of simulations called CMIP5, they found that extreme fire-weather days in autumn are likely to become more frequent as the century unfolds, and the most fire-prone autumns more often will tend to affect both northern and southern California at the same time. “Increased synchronicity of extreme fire danger between northern and southern California has the potential to hamper fire suppression and risk-reduction efforts, particularly as longer fire seasons increase fatigue among firefighters and evacuated residents alike,” the authors noted.

One semi-bright spot: if global greenhouse emissions peak by around 2040 (the RCP 4.5 scenario), the number of top-5% fire days will increase by only about half as much this century as would be the case in the high-end scenario (RCP 8.5), where emissions continue unabated through the century.

Other work suggests California will shift toward a wetter winter and drier shoulder seasons, including fall, although the crucial autumn timing – those periods when high winds strike before substantial moisture arrives – remains a topic of active research. Moreover, as the new study notes, fire is a natural part of the western landscape, and the explosion of wildfire in recent years is the result of a human-changed climate mingling with long-term patterns of land management, the flocking of people into the wildland-urban interface, and other trends.

In a tweet, Swain, a coauthor on the new paper, wrote “My approach is to be straightforward about effect of climate change (it’s making problem worse), while making clear that more fire on landscape is inevitable – it’s just a question of whether we manage it for good, or we alternate between ever greater suppression & firestorms.”

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Posted on September 8, 2020 (9:08pm EDT).

Bob Henson is a meteorologist and journalist based in Boulder, Colorado. He has written on weather and climate for the National Center for Atmospheric Research, Weather Underground, and many freelance...

43 replies on “Autumn could deliver the worst of California’s 2020 fire season”

  1. Funny thing happened on the way to the blog. In email just now I found a “Your comment has been approved!” message from about a post I made here yesterday about climate change discussion. (The text of the post was included in the email.) It posted right away. I did not know it had gone into an approval queque.

    I clicked the link in the email I received and arrived on this page to discover my comment has been removed!

    Too funny. The left hand doesn’t know what the right is doing? An old yet applicable saying. Sey Lah, people.

    (edited for clarity only)

  2. This came out twenty hours ago, updated this afternoon.
    Federal Report Warns of Financial Havoc From Climate ChangeA report commissioned by President Trump’s Commodity Futures Trading Commission issued dire warnings about climate change’s impact on financial markets.
    (More here:

    WASHINGTON — A report commissioned by federal regulators overseeing the nation’s commodities markets has concluded that climate change threatens U.S. financial markets, as the costs of wildfires, storms, droughts and floods spread through insurance and mortgage markets, pension funds and other financial institutions.

    “A world wracked by frequent and devastating shocks from climate change cannot sustain the fundamental conditions supporting our financial system,” concluded the report, “Managing Climate Risk in the Financial System,” which was requested last year by the Commodity Futures Trading Commission and set for release on Wednesday morning.

  3. All my years of following fires and their behavior, the changes and all..this has been over stimulating or overwhelming. We got a taste of this with the last round of fires in Australia, saw what was coming. To see towns lost thru friends…them thinking not everyone could have got out in time. Not even sure how many towns. It’s hard to keep up with the events, there are so many. They rescued another 150 by helicopter out of forests. 3 firefighters were hospitalized. One critical. A dozen firefighters deployed and took to a shelter of last resort…and it’s only the start of the winds and fall fire season. This is what climate change looks like.

  4. The fire and snow over the western US are just mind boggling, especially for how quickly the temperatures dropped from hot to cold preceding the snowfall in Wyoming and Colorado yesterday. Sure have interesting and challenging weather (especially with the fires) over the western US in addition to the tropics.

    Link to my latest birdseye view chart and discussion on Paulette, Rene, 94L, and the tropical waves rolling off of Africa here. In summary, thinking Paulette will approach Bermuda by early next week, possibly as a hurricane should the shearing upper vorticity break up. Rene probably will hang out east of Paulette for a few days, thinking it still can pull off become a strong hurricane in the next 3 days before upper level winds become less favorable for it. Also I think 94L is most likely to not develop before reaching the Carolina coast, never thought much of it as it only had a narrow window of favorable upper winds.

  5. Smoke column has risen so much there it’s cast a shadow on the other smoke. Close up of that. Lacks a time stamp..09092020 1640z. Click to make big.

  6. Thank You Mr. Henson for this Post on California and the heat/fire issue……This is becoming horribly tragic every year/fire season there and they are presently, and literally, caught in the “perfect” firestorm situation between the dryness/heat issues, exacerbated by global warming issues. Would note that we have also seen some very prevalent warm oceanic SST anomalies in recent years off the NW US Coast below Alaska. Don’t know to what degree degree oceanic warm flow contributes to the heat in California (with the cooler Pacific waters on the coast as compared to other parts of the US) but some of our most prevalent warm air temps/heat anomalies in the US also occur in the coastal cities along the Gulf Coast, around Florida, and back up the Eastern Seaboard all the way up to the NE adjacent to the warming Gulf and Atlantic waters.

  7. I am curious. While I am in complete and total agreement on the climate change impact and concern, some historical analyses have also shown that the recent couple of centuries in which we have populated California and other western states have actually been wetter than normal. As humans – we take such short-term views of nature, and are frustrated by the droughts and quick to blame global warming or deny it – depending on your view 🙁 – but could at least some of the impact to California may simply be the climate returning to its more historical reality?

    1. … and certainly not the speed of change.
      Last month, California set a new record for their monthly average temperature. The monthly average was 5.0 °F (2.8 °C) higher than the 1951-1980 average for August, and 1.2 °F (0.7 °C) higher than the previous record.

      1. “… and certainly not the speed of change.”

        When people say climate changes, I mention the changes we are seeing took millennia to occur.

        However, we are seeing changes on the order of decades, 2 orders of magnitude quicker.

    2. “As humans – we take such short-term views of nature, and are frustrated by the droughts and quick to blame global warming or deny it  . . . “

      Scientists are humans who in the main are professionally trained to look at all the data, not merely the short-term. When they tell us that we are seeing evidence of climate change, it’s not the same as an average human saying so or denying it.

      1. Ikr.
        When enough people scream “Stop it; we’re killing plants and animals — and about to kill most life on the planet!”
        Then the not-just-stalling discussion begins — maybe in time to save some life.

        Thanks for your post.

      2. It’s called an inverted hierarchy. Hierarchies are dysfunctional just by their nature; but when they get inverted, which they can, they can be disasters.

        Imagine if the mechanic, before turning one single wrench repairing you’re car, needed to wait for every other man, woman, and child … all over the world … to also know every detail about fixing a car engine before he could even put it up on the hoist.

        It would be ridiculous to have an inverted hierarchy like that. They wouldn’t even believe a mechanic COULD fix a car … until they understood every detail, exactly, about car motors themselves too.

        That would be stupid. That’s what we have right now. Inverted hierarchy, in our heads. It’s … almost hopeless. Until the last, dumbest man on earth understands every detail of the physics … we’re not even going to make one move. Lovely. (/s)

      3. Oh, hey, all my thoughtful insights about sociology under this comment just got removed by a mod.

        Well, there’s no point for me in embracing the new facebook mentality, so I’m just assuming from here on out that intelligent discourse about actual real climate issues is just not going to be a thing here. But I saw that anyway.

        Get it together, this is appalling moderation here. Appalling. You’re killing it, for sure.

      4. Personal disputes aren’t allowed here. Bring the sort of posts you want to see. Don’t complain about others. Would really like to see you post something about climate change instead of just about other people.

        So Tim..what part of intelligent discourse is helping us with climate change? Do find it to be a real solution? I could argue my garden is removing more CO2 than your complaints..

      5. I think ten years ago we were having serious discussions about serious issues surrounding the climate debacle. Now, we have facebook fluff.

        Waiting to see if this site was going to produce the quality and depth and nuance of the community at, say, even a site like R. Scribblers site used to years ago, has not born out. I’m not wasting my time with the ancient battle over is it really happening, or is it not even really happening. That’s all cat 6 ever got stuck on. Ya, stuck, while the rest of the not so American part of the discussion from all over the rest of the world just moved on.

        You’re not going to help anything. The debate you’re still having ended decades ago, if you’re intelligent. The other things you need to move onto talking about, never ever get discussed here. Even if someone brings them up.

        This is a travesty. I just no longer think people in this community actually get much.

      6. Yeah the debate has been over forever for many. The climate is changing. For a few that discussion still needs to happen & it’s allowed if it’s legit. If they keep asking the same questions, a bot, just here to derail or post false opinions as fact or just lies then it’s not.

        What do you think about the Federal report out about the financial chaos coming from Climate change? When climate hits the wallet it starts getting real for a lot of deniers that denied so they could keep getting fat wallet off water, air, resources we all share..

      7. Again personal disputes aren’t allowed here even ones from 10 yrs ago. Feel free to discuss weather or climate.

        The link for the report I included to Tim’s comment was wrong. That was the 2008 crisis. Having a hard time finding a link to the report or info on it that isn’t from a subscription.. From Reuters..

        The panel’s 35 members, including representatives of Goldman Sachs Group Inc (GS.N) , BP Plc (BP.L), the Dairy Farmers of America, and The Nature Conservancy among others, approved the report on Tuesday.

        “The physical impacts of climate change are already affecting the United States, and … the transition to net-zero emissions may also impact many segments of the economy,” the 196-page report said.

        “Both physical and transition risks could give rise to systemic and sub-systemic financial shocks, potentially causing unprecedented disruption in the proper functioning of financial markets and institutions.”

        A sudden shift in perceptions of the risks from frequent wildfires and intense hurricanes could bring a sudden drop in asset prices, for instance, that cascades through a community and spill more broadly into markets, the report said.

        Goes on about after this corona shock to budgets..expect even worse.

  8. Hurricane Season may get the most headlines; but this Fire Season is a mega disaster ongoing right now. In a season where firelines have never been stretched thinner, the heat and lack of rain threaten to displace a lot of people for a long time.

  9. Thanks, Bob Henson.
    Climate change is our second, world-wide greatest sin. Analogies with slavery: Arrogance and greed caused it and the repercussions reverberate and amplify with denial.

    1. If memory serves me well you are in or from Australia.
      You comment got me thinking (hard to do) so off to google I went. I had no idea that Australia was once very into slavery and worse.

      This is from wikipedia so…..not always the best source.

      Kinda long ago but……

      Many of the convicts transported to the Australian penal colonies were treated as slave labour. William Hill, an officer aboard the Second Fleet, wrote that “the slave traffic is merciful compared with what I have seen in this fleet […] the more they can withhold from the unhappy wretches, the more provisions they have to dispose of at a foreign market, and the earlier in the voyage they die, the longer they can draw the deceased’s allowance to themselves”. Once the convicts arrived in Australia they were subjected to the system of “assigned service”, whereby they were leased out to private citizens and placed entirely under their control, often forced to work in chain gangs. The unwillingness of wealthy landowners to give up this cheap source of labour was a key factor in why penal transportation persisted for so long, especially in Van Diemen’s Land where “assigned service” continued to be widespread until the 1850s

  10. Cheyenne Wyoming had a high of 32°F on Tuesday, September 8. This is the earliest in the fall a daily high has been at or below freezing. The previous record earlest date in the fall with a daily high at or below freezing was September 17, 1965.

    Santa Fe NM and Dalhart TX are observing their earliest snowfall observations on record on September 9..

  11. Love ya Bob. Own your book(s) and have given and recommended them.

    Keep writing, as there’s a lot more to ferret out here.

  12. Thanks Mr Henson.

    Here’s a link to a site where you can actually spot the fires easily from a satellite loop:

  13. Thanks Mr. Henson, fascinating And terrifying read. I fear for all of us and only hope we can adapt fast enough to survive these extremes.

  14. I wonder if California will have 3 million acres burned this year. Shattering their record like Australia did.

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