Reviewing Those California Wildfires

I know I’m pretty darn late to this blog – these wildfires have occurred two weeks ago. But I would be remiss if I did not at least write a little something about the devastating fires that have caused so much destruction over California. Two fires in particular – the Woolsey Fire near Los Angeles in Southern California and the Camp Fire in Butte County in Northern California – have collectively scorched 250,000 acres, incinerated over 20,000 buildings, and caused billions of dollars in damage. With 84 confirmed fatalities, the Camp Fire is the deadliest fire since the Cloquet Fire in Northern Minnesota of October 1918, and with 475 (as of 11/24) people still missing, the final death toll could be higher.

The Meteorological Setup:

The Woolsey Fire was fanned by the “Santa Ana” winds that are notorious for bringing abnormally warm temperatures, very low dewpoints, and very high fire danger to Southern California. The Camp Fire was spread by the lesser-known “Diablo Wind” that flows down the slopes of the Sierra Nevada into the Sacramento Valley and San Francisco Bay Area. The image below, which is the 10-meter wind speed forecast from NOAA’s HRRR (High Resolution Rapid Refresh) model, shows the strong Santa Ana and Diablo winds over their respective parts of California as they were predicted to be at 12 pm on Thursday 11/8/2018.

Both the Santa Ana and Diablo Winds are specific examples of “foehn winds” – strong, warm, dry downslope winds on the lee side of a mountain range. The term originates from the warm, dry wind in the leeside of the Alps that warmed Central Europe while the windward sides of the Alps experienced the brunt of powerful extratropical cyclones coming off the Atlantic into the region.

Santa Ana and Diablo winds are much more common in the autumn than the summer. This is because you need high pressure over the Great Basin to drive these offshore winds, and the summertime heat over the Great Basin and Desert SW tends to create a thermally-induced area of low pressure. The ideal pattern for Santa Ana and Diablo winds is to have a deep upper-level-trough push southward from Canada into the Intermountain West, cooling temperatures there and increasing the surface pressure. Additionally, this trough displaces the pre-existing, mild airmass over the region and pushes it west off the Californian coast, creating a thermal trough off the coast and very strong offshore pressure gradients.

As the surface and upper-level charts below show, this was a classic foehn wind event for Califonia. A large trough plunged southward from Canada, increasing surface pressure over the Great Basin and displacing a ridge of high pressure/thermal trough to the west in the process. This created strong offshore gradients and powerful Santa Ana and Diablo winds.

Evolution of the Fires

The Camp Fire was first reported at 6:33 am PST on November 8 when a transmission line owned by Pacific Gas & Electric (PG&E), a California Utility, collapsed in the strong winds. The fire grew to a staggering 18,000 acres by the evening as strong, dry, northeasterly Diablo winds fanned flames and carried embers downwind, starting new blazes. It wiped out the town of Paradise and the unincorporated community of Concow the very same day.

The fire continued to grow explosively through 11/9 as Diablo winds approaching 50 mph persisted, and by the morning of November 10, the fire had grown to 100,000 acres. Wildfires are not my area of expertise, but you don’t need a degree in meteorology to know that a fire that grows to 100,000 acres in two days is a force to be reckoned with.

Another Hazard: Air Quality

The fire grew at a lesser rate after the 10th as the ridge of high pressure offshore moved over the area, substantially weakening the offshore gradients and Diablo winds. But the light offshore winds blew the Camp Fire smoke plume into highly-populated San Francisco Bay area, and the long-lived ridge of high pressure over the region ensured that extremely poor air quality persisted for days.

The picture below offers a comparison between 11/16/2018 (left) and 10/14/2018 (right) of the view from the Oakland-San Francisco Bay Bridge. It’s not like 10/14 was a stunningly clear day either!

Air quality finally improved earlier this week as increasing onshore flow pushed this smoke out of the area, and heavy rain on Thanksgiving and Black Friday over Northern California helped firefighters make significant progress containing the fire. As of Saturday 11/24, it is 95% contained, and full containment is expected by 11/30.

The Woolsey Fire began later Thursday afternoon, and like the Camp Fire, it grew incredibly quickly under strong Santa Ana winds. Southern California also saw several days of “Very Unhealthy” air quality as smoke remained over the region. The cause of the Woolsey Fire is currently unknown, but a class-action lawsuit has been filed against Southern California Edison, who the plaintiffs claim is responsible for the fire based on the fact that the fire began near poorly-maintained Southern California Edison electrical equipment.

As you would expect, PG&E has received a ton of criticism for their failure to de-energize their transmission lines in the face of extreme fire danger. Their stock plummeted 63% from 11/8 to 11/15 before rebounding 38% on 11/16 when the California Public Utilities Commission (CPUC) reported that they will take into consideration the utility’s financial health when weighing a request to cover costs associated with wildfires. Southern California Edison is a much smaller company and did not see as drastic of a drop in their stock price as PG&E, but the stock still lost a quarter of its value between 11/8 and 11/15 before making up some of those gains on the 16th.

Hindsight is 20-20 of course, but given the critical fire danger, PG&E should have de-energized these lines.

How Can We Prevent This From Happening Again?

Well, I’ll start off with the obligatory disclaimer that I know relatively little about wildfires and even less about precautionary measures that can be taken to reduce the risk of these blazes from occurring. But one thing I have noticed with respect to any natural disaster is that our poor preparation for these disasters costs us far more than adequate preparation would. Postponing routine maintenance, or just “hoping” that a worst-case scenario does not come to fruition, is not only irresponsible – it is uneconomic. One of the best examples of this is the threat of a Cascadia Earthquake in the Pacific Northwest. Earthquakes can be predicted with certainty due to the gradual buildup of stress along a fault line compared to the chaotic nature of individual storms, so the fact that we are not pouring in tons of money into retrofitting or destroying buildings not capable of surviving these earthquakes shows our favoritism for short-term economic growth over long-term safety and sustainability.

Just some food for thought, in case you haven’t had enough food this weekend!
Charlie