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.
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.
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.
