My group and scientists from the University of Albany are now studying the meteorology of the LA wildfires earlier this month and have significant early results. At the American Meteorological Society meeting last week, I attended many wildfire meteorology sessions and talked to several colleagues who have actively studied such events. The LA fires were a topic of considerable discussion.
We have a good idea of what happened: an extreme/unusual Santa Ana event associated with severe downslope winds. In this blog, I will show you some early simulations and explain why this event occurred.
I will also describe why climate change did not play a significant role.
As I will explain below, this is not only a Santa Ana event, but an unusual one, with extreme winds descending to lower elevations. Some lower-elevation stations, such as Burbank, experienced their strongest wind gusts on record. Model simulations suggest the development of what is known as a high-amplitude mountain wave leading to a downslope windstorm event.
Santa Ana 101
Santa Ana's are associated with strong northeasterly (from the north to east) winds over southern California. These strong winds are accompanied by very low relative humidity and are very favorable for southern CA wildfires.
The typical large-scale weather pattern associated with Santa Anas includes a large high-pressure area over the Great Basin, with the strongest events also having a low center to the southwest (see below). Such a pattern results in strong northeasterly winds approaching the mountains of southern CA.
The observed sea level pressure pattern at 4 PM January 7 (below) showed many of these elements, with the low to the south being particularly strong (warm colors indicate above-normal pressure, cool colors show below-normal pressures).
This pattern produced extreme, perhaps unprecedented, northeasterly winds approaching the region in the lower atmosphere. To illustrate, the color shading in the map below shows wind differences from normal at 925 hPa (about 2500 ft above sea level) at 10 PM Tuesday (January 7) evening. The light gray indicates very unusual winds (more than six standard deviations from normal). The wind direction and speed at some points are also shown.
This was not your normal Santa Ana.
High-Resolution Simulations
To understand what is going on, it is useful to plot vertical cross-sections through the fire areas to show the 3-D atmospheric structure. Below is a cross-section (at 8 PM Tuesday) through the Eaton fire; a section that crosses the San Gabriel Mountains. The shading shows sustained winds in knots, the x-axis is the horizontal distance and the y-axis is height in pressure (700 is about 10,000 ft)
.gif)
Another cross section, this time going through the Palisades fire at 10 AM on Wed. January 8, is shown below. Very strong winds to the lee (south) of both the interior mountains and Santa Monica mountains to the south (left side of the figure).
These and earlier simulations by the UW WRF model and NOAA/NWS models (such as the HRRR, High Resolution Rapid Refresh) consistently forecast the extreme downslope winds DAYS in advance.
For the Palisades inferno, it is either some smoldering embers from a New Year's Eve fireworks blaze or the failure of some aged powerlines found north of Skull Rock. Perhaps, arson is another possibility. Several fire experts I talked to at the AMS wildfire meeting thought the powerlines were the most probable cause, but a definitive evaluation is not yet available.
3. There are some outrageous claims that the LA fires are the result of increasing "weather whiplash" due to climate change. This "whiplash" theory is unsupported by observations, such as the plot shown above.
High-Resolution Simulations
To understand what happened, UW Research Scientist David Ovens, a member of my research group, ran a very high-resolution forecast/simulation of the event using the WRF model, with a grid spacing of 1.3 km (this is very high resolution).
Let me show you a surface wind gust forecast (32 hours into the prediction) for 12 AM on Wednesday, January 8. The areas of the Palisade and Eaton fires (the two biggest ones) are shown by red outlines.
Extreme winds (with gusts exceeding 70 knots, 81 mph) were forecast over and downwind of the San Gabriel Mountains. HUGE threat. Lesser, but still strong winds (50-60 mph gusts) are noted in the Palisades area extending to the west and south.
To understand what is going on, it is useful to plot vertical cross-sections through the fire areas to show the 3-D atmospheric structure. Below is a cross-section (at 8 PM Tuesday) through the Eaton fire; a section that crosses the San Gabriel Mountains. The shading shows sustained winds in knots, the x-axis is the horizontal distance and the y-axis is height in pressure (700 is about 10,000 ft)
Wow. Very strong acceleration of the air as it descends the southern slopes of the San Gabriels, with the strongest winds near Altadena, where the fire went crazy. This was a very powerful downslope windstorm with a highly amplified mountain wave pattern.
.gif)
Another cross section, this time going through the Palisades fire at 10 AM on Wed. January 8, is shown below. Very strong winds to the lee (south) of both the interior mountains and Santa Monica mountains to the south (left side of the figure).
These and earlier simulations by the UW WRF model and NOAA/NWS models (such as the HRRR, High Resolution Rapid Refresh) consistently forecast the extreme downslope winds DAYS in advance.
It was also clear that there were unusually large amounts of dried "fuels" ready to burn. The fuel load was particularly high after TWO unusually wet winters (2022-2023, 2023-2024). A dry start of winter ensured massive amounts of fuels were ready to burn.
This was clearly a situation of extraordinary extreme wildfire danger. That is why I blogged a strong warning the day before. Why the National Weather Service did the same. LA officials should have know a severe threat was in place.
All that was needed was an ignition source. For the deadly and large Eaton Fire near Pasadena, it appears that a problematic electrical transmission tower was the origin of the fire.
For the Palisades inferno, it is either some smoldering embers from a New Year's Eve fireworks blaze or the failure of some aged powerlines found north of Skull Rock. Perhaps, arson is another possibility. Several fire experts I talked to at the AMS wildfire meeting thought the powerlines were the most probable cause, but a definitive evaluation is not yet available.
What is clear is that LA did not shut off the power to the region even AFTER the fire was initiated and that only limited fire-fighting resources were in place before the fires began. Not good.
Bottom Line: A very skillfully predicted Santa Ana event with record-breaking winds hit LA earlier this month. Two wet winters resulted in unusually high levels of dried fuels. Human ignitions initiated the fires.
Influence of Global Warming
There are several media outlets and climate activists that are suggesting that LA fires were the result of global warming or significantly enhanced by human-caused warming.
These claims are contrary to the best science, which indicates minimal impacts of human-caused warming.
Such claims undermine the importance of key societal failures, from not shutting off power and fire-hardening homes to not having sufficient fire-fighting capabilities or adequate warnings and evacuation protocols.
Key reasons why global warming is not an important factor include:
Key reasons why global warming is not an important factor include:
1. There is no evidence that global warming increases Santa Ana winds. In fact, there are strong physical reasons (with supporting scientific literature) that global warming WEAKENS Santa Ana winds.
2. The available fuels were unusually abundant because the two previous years have been much wetter than normal. There is no evidence this is caused by global warming. And there is no long-term trend for wetter winters, which would be evident if this was a climate issue.
3. The immediately prior months were drier than normal. This is not predicted by global warming projections and there is no historical trend to drier early winters which would occur if climate was a cause (see plot below of Los Angeles precipitation for Oct. 1-January 6 ).
3. There are some outrageous claims that the LA fires are the result of increasing "weather whiplash" due to climate change. This "whiplash" theory is unsupported by observations, such as the plot shown above.
I am particularly troubled by the media pushing weather/climate theories that are untrue. A prime example is the unsupported claim that the Lahaina fire was associated with the passage of a hurricane to the south. This was proven to be false.
You said a couple of weeks ago that the jet stream shift to the south could bring precipitation to Southern California. Didn't happen. Do you see any precipitation for that region in the near future?
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteThanks....as you note, SL pressure gradients are better for gaps in mountain ranges than when mountain waves are critical (as in this event)..cliff
Delete"There are some outrageous claims that the LA fires are the result of increasing "weather whiplash" due to climate change. This "whiplash" theory is unsupported by observations, such as the plot shown above."
ReplyDeleteActually the trendline of year-to-year changes in precipitation from that plot is increasing, and 4 of the top 5 year-to-year changes have been in the last 20 years (the graph is ~75 years worth of data).
ChrisC....you are not correct. I also plotted the year to year changes. No increasing trend. There is no increasing "weather whiplash". In a future blog I will discuss this..cliff
DeleteNeeded to correct a few of my mistakes on my original post.
ReplyDeleteCurtKapJanuary 19, 2025 at 8:57 PM
One other tool used to get an idea of the strength of offshore winds, are by looking at designated surface pressure gradients. LAX-DAG gradient is a good indicator of NE-SW direction. (Typical Santa Ana wind direction). During the initial afternoon through evening on Jan 7th. The LAX-DAG gradient was not very strong, In fact the LAX-BFL gradient (N-S direction) was a few mb stronger. The placement of the upper low over Baja/ AZ had a lot to do with energizing this damaging Santa Ana with cold upper level flow moving in a parallel direction with the cold denser air wanting to subside. If there is an inversion near the mountain tops around 700 mb, mountain waves are able to crash down on the leeward side of the foothills, valleys and coastal areas. Cliff mentioned all of the reasons and showed the graphs to back it up. My 2 cents:Typical LAX-BFL gradient winds ( not including strong upper support) affects the I-5 corridor including Castaic below the Tejon Pass, Santa Clarita, Central and eastern San Fernando Valley including Sylmar, Burbank. Van Nuys, and through the Sepulveda Pass and Hollywood Hills to Santa Monica and Pacific Palisades. The LAX-DAG gradient typical NE-SW direction (more typical Santa Ana wind direction) generally affects the mountains of LA and Ventura Counties into The Hwy 14 corridor including Acton, Canyon Country and Santa Clarita, then western San FernandoValley, much of Ventura County to the coastal plain. Also the Santa Monica Mtns usually Malibu and areas west. (Lighter breezes for Pacific Palisades). Also the passes and canyons in the San Gabriel Valley including Eaton Cyn. If upper support is strong. Then mountain wave activity can bring surfacing damaging winds across the 210 and 118 corridors. I've worked many of these strong Santa Ana and I-5 corridor events. Relatively cold winds drive stronger and more widespread stronger events. The addition of
mountain wave activity can bring more damaging winds to areas not usually affected. Nice write up Cliff!
"The immediately prior months were drier than normal. This is not predicted by global warming projections..." That is not correct, Cliff. Drier than normal conditions are predicted by global warming projections. For example, according to the Fifth National Climate Assessment, Section 28 (Southwest): "Higher temperatures have intensified drought and will lead to a more arid future (very likely, high confidence); without adaptation, these changes will exacerbate existing water supply–demand imbalances (likely, high confidence)."
ReplyDeleteNo, Jerry... the model projections agree with my statement. Precipitation will increase in coastal SW CA under global warming. Temperature will increase, but so will precipitation.
DeleteIn your earlier blog on the LA fires you state that drought was not a factor for this fire, due to grass and fine fuels having a short drying period, and you show a graph of water season precipitation amounts back to the early 1950s. In December of 2011 Los Angeles experienced a very strong Santa Ana wind episode with winds also over 100 mph and much tree and power line blowdown. Yet, fire was not a significant factor during the 2011 episode. A likely factor was that precipitation during that 2011 period, according to your graph, was near the greatest for this period, only one other year showing a little higher amount, while 2024 had the least amount during this period. You have stated in blogs on grass fires in the Pacific Northwest that drought is not a factor. Most of the grass fires that I am familiar with in Eastern Washington have occurred during and following significant dry periods such as the 2014 Carlton fire in the Okanogan and the 2023 Gray fire near Spokane, both of which also had significant warm weather associated, and both of which destroyed many structures. While grasses and light fuels can dry out quickly, I believe that historically, most of our large grass fires had associated drought conditions.
ReplyDeletewxman.... This event was stronger than the 2011 event. There was considerable more fire equipment available during that event. It was not preceded by two years of heavy winter precip..which led to abundant growth this time around. There was less development up in terrain. And the power infrastructure was 15 years younger....cliff
DeleteWxman, Carlton and Okanogan Complex fire both were multiple lightning strike fires and burned for days before the major growth, merging and destruction events. For years, the story was smoke jumpers wanted to jump on the fires that started the Carlton complex, but were turned away by the state who had jurisdiction. If these fires were fought aggressively during their initial starts the destruction may have been avoided. Cliff can attest, but generally we on Eastside see "drought" every year according to their drought monitors. We have a dry season, months without rain or very little. But those two fires had days of burning and fuels drying to get a running start. They weren't started by dry lightning either. They smoldered in heavy fuels with little growth the first few days. Further they were in mixed fuels of heavy this trees, downed tree, underbrush, and grass before coming to the the grass shrub of the valley.
DeleteAll that to say again, those fires had days of drying after they started and the fine fuels dried quickly helping carry the fire quickly. So cliffs observations still hold.
DeleteAccording to the downtown Los Angeles reporting station, the two years prior to the December 2011 event, were also wetter than normal, although not as wet as the two prior to this recent event. However, December of 2010 saw over 10 inches of rain, the second wettest December of their long term record (which goes back to 1877). Also the months of October and November of 2011 had twice the normal rainfall at this station so I would think that the more abundant moisture prior to the 2011 wind event was likely a factor in the absence of fire.
DeleteClearly, heavy rain at or immediately prior to a strong Santa Ana events reduces fire intensity. There is no argument with that. Remember the 2011 fire occurred in very early December and late Novemember
DeleteSo now we have weather whiplash, heat domes, and bomb cyclones? You know if we just did away with public access to the internet, most of our "problems" would magically vanish.
ReplyDeleteCliff, your analysis absolutely "nailed it". This was most definitely NOT an ordinary Santa Ana event, but one with high winds aloft driven by "a high amplitude mountain wave leading to a downslope windstorm event" as you said. I am a retired NWS aviation (CWSU) forecaster with over 55 years experience in this region. As a glider pilot and soaring forecaster... we are all very well aware of these mountain waves and their impact on aviation besides the high wind erratic gusts that can trigger these events. Air Force One chose not to fly on Wednesday Jan 8th due to the severe turbulence. Communication of the forecasts seems to be the problem. NOAA/NWS Oxnard warned of this at least 5 days out. I know that NWS reached out to the decision makers and others as best they could. But, somehow, the gravity of these extreme events isn't getting through...
ReplyDeleteCliff, your analysis absolutely "nailed it". This was most definitely NOT an ordinary Santa Ana event, but one with high winds aloft driven by "a high amplitude mountain wave leading to a downslope windstorm event" as you said. I am a retired NWS aviation (CWSU) forecaster with over 55 years experience in this region. As a glider pilot and soaring forecaster... we are all very well aware of these mountain waves and their impact on aviation besides the high wind erratic gusts that can trigger these events. Air Force One chose not to fly on Wednesday Jan 8th due to the severe turbulence. Communication of the forecasts seems to be the problem. NOAA/NWS Oxnard warned of this at least 5 days out. I know that NWS reached out to the decision makers and others as best they could. But, somehow, the gravity of these extreme events isn't getting through...
ReplyDeleteImmediately prior to the LA wildfires, ample warnings were voiced from those professionally qualified to do so, and those with an assigned responsibility to do so, that a loaded cannon was pointed directly at people and at property, and that the danger was both extremely acute and extremely serious.
DeleteLack of effective communication was not the problem. Not at all. In the days immediately preceding the wildfire event, timely warnings came from those whose job it was to issue those warnings. The warnings could not have been any more clear or any more timely than they were.
What happened is that those timely warnings were consciously and deliberately ignored by Los Angeles city officials, by LA County officials, and by California state authorities as well. My further commentary on that score is here:
Beta Blocker's WUWT Comment on the LA Wildfires, 01/15/2025
"What happened is that those timely warnings were consciously and deliberately ignored by ...." is simply your political right leaning decision, Mr Betah Blocher. It has no credibility on this forum.
DeleteFrom Hydroclimate volatility on a warming Earth, Nature Reviews Earth & Environment 1/9/25
ReplyDeleteDaniel Swain et al, NCAR
"Using a metric of ‘hydroclimate whiplash’ based on the Standardized Precipitation Evapotranspiration Index, global-averaged subseasonal (3-month) and interannual (12-month) whiplash have increased by 31–66% and 8–31%, respectively, since the mid-twentieth century. Further increases are anticipated with ongoing warming, including subseasonal increases of 113% and interannual increases of 52% over land areas with 3 °C of warming; "
This paper is deeply flawed. I will discuss it in a future blog...cliff
DeleteNot sure what to root for: Wet winter where plants have increased growth which leads to more fuel? Dry winter where plants dry out and ignite easier? What is the Goldilocks scenario? Not that my rooting can change things, though.
ReplyDelete