December 05, 2017

Another Highly Predictable Windstorm/Wildfire Event: Ventura and Los Angeles Counties

It has happened again:  a major wildfire event initiated by strong offshore winds.  Again, the winds were caused by cool, high pressure moving into the intermountain west.  And again, the forecasts were stunningly good.  And I
suspect, again, problematic power lines will be involved in starting the fires.

Wildfires are burning right now in Ventura and Los Angeles counties, with the largest fire (the Thomas fire impacting Ventura, CA) starting in the hills and then descending down to town (just like the Tubbs fire that hit Santa Rosa on October 8-9).

As I write this, the Thomas Fire is out of control, having consumed more than 50,000 acres, with other fires on the southern slopes of the terrain surrounding the LA Basin (see map of its current extent).  

Over 200 buildings have lost, and more will soon join them.  The fires started abruptly as winds picked up late in the afternoon on Monday.  We went from nothing to tens of thousands of burnt acres in a few hours.   The NASA MODIS satellite tells a stunning story, with no smoke or fires yesterday and multiple large fires around noon today (see below).

The fires began around dinner-time Monday as strong, dry Santa Anna winds revved up.  Here are the maximum wind gusts for the 24h ending 7 PM Tuesday. A number of locations got about 60 mph (purple color), with several getting up into the upper 70s.  Huge variability in the winds, depending location and exposure.  These strong winds were from the northeast.

Over 200,000 customers were out of power by late Monday.  

Let me show you a sample of the wind evolution at a mountain site, Chilao, CA, located at 5490 ft in the hills north of Los Angeles.  Winds increased rapidly yesterday and around 72 mph starting around 4 PM Monday.  Now dropping but still strong.

Interestingly, temperature COOLED as the winds increased from around 50F to the lower 30sF as the winds increased.  This event is not about heat, it is about dry air and wind.

 The whole event was caused by cool, high pressure moving into the Northwest (yes, us!) and then southward into Idaho and Nevada (see map for 1 AM today, showing the pressure analysis).

 This pattern produced an offshore pressure gradient (higher inland, lower along the shore), which in turn produced offshore (easterly and northeasterly) winds over southern CA.  These winds were strengthened by their interactions with the substantial terrain of the region, producing what is known as Santa Anna winds.

 Numerical weather prediction models run by the National Weather Service and others skillfully forecast this event days before, with the predictions the day before being dead on.   For example, the Desert Research Institute (DRI) WRF model prediction initialized at 4 AM Monday showed huge sustained winds over the region later that day (forecast for 10 PM Monday is shown).

The forecast made two days before for the same time was essentially the same...and very threatening (see below).   So this event was highly predictable.

The National Weather Service High Resolution Rapid Refresh (HRRR) model initialized at 4 AM Monday predicted strong winds in the area later that day.  I could show you more forecasts, but the message is clear:  my profession has now gained the ability to skillfully forecast such downslope wind events days before.

 And the National Weather Service forecasters were providing excellent guidance, pushing the severe threat in their communications on Monday, before the fires started (see below).  Excellent messaging.

Could this have all been avoided?

Let me ask the same question I offered in my blogs on the Wine Country fires.

We had nearly perfect weather forecasts that called for very strong winds over and downwind of the regional terrain.  The fuels (grasses, bushes) were very dry. Their was a strong probability that power would be lost in large areas and that power lines could start fires, which would explosively develop.

So why not preemptively shut off the power, to all the power lines that ran in the vegetated hills?   Could we have stopped this growing disaster from ever happening?

Power companies and those in responsible positions need to rethink about how they respond to these predictable wind events.  We can radically reduce the damage toll and loss of life by taking more active measures, informed by excellent weather forecasts.


  1. Cliff,

    As always, a well-reasoned article. Of course, the issue is that too many people wish to bury their heads in the sand when presented with a forecast (meteorological, stock market crash, etc.) of some adverse condition. Here we have people who don't even put their most precious belongings in their cars when one of these forecasts is issued.

    We also have to weigh the damage (not the deaths) against the loss to the economy of California when the power is out for days (as it would be in this case).

    Tough problem.


  2. Underground power lines would be even better.

    I believe a strong low pressure system can also cause a Santa Ana because it pushes all the dry air to the southwest. Thus we get northeast winds.

  3. Shutting off power is ultimately a political question, I don't think a power company would be allowed to make the decision. Could courts hold power companies responsible? It could happen but would be a bad decision and bad politics. I imagine that these questions are being discussed in the industry and with government.

    And the second question is how much are power customers willing to pay? Given the current power distribution system turning off power during peak winds is reasonable, but is it politically possible?

  4. Cliff,
    You are making the assumption that these fires were caused by power lines down. They may have been but some of the biggest fire in SoCal History have been caused by arson (Station Fire 2009) or stupidness (Ceder Fire 2003, which I fought). You can predict when the Santa Ana wind blows that the fire bugs will come out and you will be without sleep until the winds die down.

  5. Josh,
    Of course I can not exclude arsonists, but the simultaneous initiation of fires just as the winds surge are suggestive of powerline initiation. This happened with the wine country fires and apparently with this round of fires. The issue about good warnings of extreme danger is the removal of vulnerable folks from dangerous locations and preparations for evacuation in such areas. But in any case, why take the chance with electrical fires? ...cliff

    1. What happens, though, if you turn off the power and people are unable to get communications (tv, radio, internet) - and then a fire starts anyway, from another source, and no one can be warned. Couldn't that be a much more deadly event?

  6. I agree with Carol that burying power lines in high risk areas is the best solution. When one considers the costs of maintaining above ground lines and the fire risk, it makes sense. But there are a lot of other causes of brush fires, not the least of which is off road vehicles. Also large trucks dragging their chains and the old standby - people throwing cigarette butts out their car windows.

  7. Keep in mind that the power cannot be turned on when the winds die down. Instead, all the damaged lines/transformers need to be repaired first -- a lengthy process. In cases where this prevents a massive fire, that might be a good trade-off. However, when there are 'false-alarms' that wouldn't have produced a massive fire, the social cost of an extended power outage would be prohibitive. I'm going to assume that only a small percentage of damaged lines/transformers actually start substantial fires, so false alarms would regularly occur. Burying the lines is a great idea, but probably cost prohibitive. Power companies do spend a lot on line maintenance like trimming back trees, etc... Perhaps they should put more effort into reasonably "wind proofing" their lines.

  8. For those asking for the installation of underground power lines, while that would help alleviate much of the current fire hazards going on in CA, it's also quite expensive. I grew up in a high wind, rural area that had so many power lines going down yearly that it made sense to bury the lines, but it came at an high cost - to the consumers. Additionally, when the lines inevitably broke it was expensive to dig them up and repair them. So it's a worthwhile suggestion of course, but will the consumers pay for it?

  9. Of course not Eric and thanks for the perfect metaphor for the risk of climate change!

    So long as the abstract notion of a huge fire burning your entire town remains way off in the warm and fuzzy future, this months cheque book balance rules all decision making, especially if the long awaited holiday in Mexico is at risk.

    Then comes the day when action is too late.

    This is called "loss aversion" which is another term for "risk incompetence".

  10. The primitive nature of our electrical distribution system is a huge part of the problem.

    The technology easily exists to sense what is going on with power lines and towers/poles and to locally cut power when they exceed certain parameters. The motion of lines and insulators and poles/towers can be instrumented, and localized switches can be installed to respond to excess motions or current shunting, etc. without intervention, and then notify repair and emergency people.

    Not a technology issue at all, and it would likely be a lot cheaper than burying lines. But still costly compared to doing nothing (at least for the electrical utility).

    But Bruce Kay's "loss aversion/risk incompetence" points are well taken. The legal, insurance, governmental and social systems of the country have always tolerated losses due to "Acts of God/Nature", or even crime (arson) as long as things are built and managed to reasonable (meaning traditional) standards.

    There are several ways to break out from this, but I suppose until we humans are controlled by a benign but authoritative Artifical Intelligence (which always makes the most rational, long-term decisions), then we're stuck with making short-term decisions.

    Which in the case of most of the people who lose their houses in fire means to rebuild in the same place, using materials that are more or less as flammable as the ones that burned.

    (Making houses from materials that won't burn and establishing defensible fire breaks is another available technology, but it costs more than nailing extremely flammable sticks of wood fuel together).

  11. Bruce Kay - excellent post, had me chuckling and nodding my head. Individual wealth and short-term comfort always has and always will drive the decision making, at least up until we evolve into something beyond glorified chimps.

    Yes there is global warming, but there are also Mai Tais waiting for me down at the air conditioned bar. Decisions decisions..

  12. Shutting off the power, on the face of it, sounds like a great idea. However, as William and Rose George alluded to, doing so has potentially life-threatening consequences. Not just in the realm of communication, but also in the arena of people at home (and even in facilities) hooked to life-saving equipment.

    I think burial, while expensive, is a good solution. As better means for energy storage becomes available, it might also be possible one day to shut off those transmission lines in a situation like this, but that's a ways off.

  13. It is clear to me now. California needs to revise its building codes so that houses and other buildings are made highly fire-resistant. Brick or stucco walls, tile or metal roofs, even ready-to-deploy fire-shields. And developers ought to be planting plants of low flammability. Deciduous trees but not conifers, cacti not bushes, stone gardens around the house itself.

    If the ecosystem is a tinderbox, you have no business with a wood structure.


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