Climate, Science

Wildfire Outlook Update

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Last week, the Bootleg Fire, a 400,000 acre conflagration that is still only 40% contained, made headlines when it tripped off a set of high-voltage transmission lines known as the California-Oregon Intertie that transmit electricity between the Pacific Northwest and California. At the time, California was experiencing an extreme heat wave and very high electricity usage, so the combination of above-average energy usage and the limited ability to import electricity from the Pacific Northwest meant that California had limited supply during a period of very high demand.

Credit: The Oregonian

The California Independent System Operator, which is responsible for operating California’s electric grid by doing things like balancing supply and demand, ensuring transmission availability, and economically dispatching electricity from power plants to member utilities’ balancing authority areas, issued several “Flex Alerts,” asking people to reduce power usage to reduce the risk of rolling blackouts.

The Bootleg Fire has seen extreme fire activity as strong winds push it through dry timber. It has even caused “pyrocumulonimbus” clouds, which are clouds that are created as the hot air from the fire rises and cools until it reaches saturation. Some of these clouds exceeded 44,000 feet and were associated with thunder and lightning.

View of the Bootleg Fire. Credit to the 141st Air Refueling Wing Washington Air National Guard. Note the cloud top flattening as it reaches the tropopause
Retrieved from InciWeb

But it’s not just the Bootleg Fire that is burning. As of 7/18, Northwest Interagency Coordination Center counts 16 “large fires” (>100 acres in timber or >300 in grass/brush). I thought my Twitter post labeling the fires visible from space would just take me a few minutes but it turned out to be a project in itself.

So far, the 2021 fire season has dwarfed the 2020 fire season year-to-date in terms of acres burnt over Washington and Oregon. And this has occurred without any major dry lightning outbreaks over Washington or Oregon. Fuels are just so dry right now that all it takes is a spark to begin a wildfire, and we’ve had persistent moderate-to-strong onshore flow over Central and Eastern Washington and Oregon that has helped these fires continue to grow.

With the extreme fire activity already witnessed east of the Cascades, the record-dry spring over much of Oregon and California and record drought over much of the Western US, and the cataclysmic 2020 fire season still very fresh in people’s minds, there is understandably a lot of anxiety as we approach the peak fire season west of the Cascades, which is approximately from mid-August through September but can extend into October, depending on when the first rains of autumn arrive.

I’ll start this blog off with an outlook for the rest of the 2021 Pacific Northwest fire season. The second part of this blog will review the two major fire weather events in 2020 – the mid-August California lightning fires and the catastrophic Labor Day windstorm/firestorm throughout Washington, Oregon, and California. I never really got a chance to blog about these last year since I was so busy with fires for work, but they definitely deserve a little discussion.

2021 Wildfire Season Forecast
I’m expecting well-above-average wildfire activity over Washington and Oregon for the remainder of the summer and autumn due to the ongoing drought across the Western US and well-below-average fuel (i.e. vegetation) moisture. This is particularly true for larger, thicker fuels due to our long-term drought, and these thick fuels are the biggest energy source for fires that burn through timber, particularly the dense timber that exists west of the Cascades.
Fuel moisture of “1000-hour fuels,” which are fuels that can take up to 1000 hours to react to moist conditions. This includes fuels 3″-8″ in diameter, such as trees or large brush piles.
Credit: Northwest Interagency Coordination Center
Additionally, the drought has worsened substantially over the Pacific Northwest over the past month due to the dry and record-hot weather we’ve seen. “Extreme” drought now extends through the Northern Willamette Valley, and an incredible 27% of Washington is now in “Exceptional Drought,” the highest on the US Drought Monitor scale. A month ago, none of Washington and only a small part of South/Central Oregon was experiencing Exceptional Drought. Not surprisingly, the Bootleg Fire is burning through this “Exceptional Drought” portion of South/Central Oregon.
And unfortunately, the forecast through early September calls for continued warmer and drier-than-average weather, with worsening drought conditions. I suspect the “Extreme Drought” currently over the Northern Willamette Valley will spread to Portland by the first or second week of August.
Credit: WeatherBell
Credit: WeatherBell
From now through September, the primary fire threat for areas east of the Cascade Crest is a dry lightning outbreak. With fuels as dry as they are, the probability of a lightning strike resulting in a successful fire start is well above-average, and a prodigious dry lightning outbreak would create an extreme amount of new fires. Lightning of any sort is not expected for the next 7 days, but it bears extremely close watching.
West of the Cascades, the primary wildfire threat is from strong, dry offshore winds. These winds are most common after mid-August, with September being the highest risk month. By October, fuels are generally too wet, but there have been Octobers with extreme fire danger west of the Cascades. October 1991 was one such month; the video below shows the 1991 Falls Fire racing through the Columbia River Gorge.

My single biggest worry from now through the end of fire season is an offshore wind event over critically dry fuels, particularly after mid/late-August. As I’ll explain in part two of this blog, the probability of us seeing a September 2020-style event is small due to the rarity of such an event. However, a “garden variety” east wind event, like the fire above or the Eagle Creek Fire from September 4-5, 2017, would still result in extraordinarily high fire danger. Click here to read the post I wrote back in 2017 on the Eagle Creek Fire.
I’ll end with this: it’s not a matter of if we will see offshore flow or dry thunderstorms for the remainder of the year, it’s a question of when and how strong. The below fire prevention tips are more important now than ever. Let’s hope for the best, prepare for the worst, and we’ll get through this together.

Part 2: 2020 Fires Review

The Mid-August 2020 California Lightning Fires

In mid-August 2020, California experienced an unusual pattern, with an extremely strong ridge of high pressure over the Western US and strong southerly flow along the West Coast that brought moisture from the remnants of Hurricane Elida and Tropical Storm Fausto northward.

This combination of very strong ridging and tropical moisture resulted in two things. The first was a record-breaking heatwave with unseasonably humid conditions, resulting in extraordinary heat indices and very little overnight relief in temperatures, as water vapor is a strong greenhouse gas and helps prevent heat loss at night. Demand skyrocketed during the heatwave, and California had to implement rolling blackouts for the first time since the California Electricity Crisis from 2000-2001. But unlike the 2000-2001 energy crisis, which was due to energy traders artificially reducing supply and taking advantage of the increased prices, the 2020 energy crisis was due primarily to extreme temperatures. A fun fact about the 2000-2001 energy crisis: it greatly (and undeservedly) harmed then-Governor Gray Davis’ standing, and a certain Austrian bodybuilder won in a 2003 recall election.

Yup, the Governator’s successful gubernatorial bid was primarily due to an energy crisis! If you are interested in a great documentary on Enron & the California Energy Crisis, I recommend watching “The Smartest Guys in the Room.”
Credit: Dale Frost

The other main impact of this ridge/tropical moisture combo was unusually strong thunderstorms over the San Francisco Bay area with gusty winds, extremely frequent lightning, and little precipitation. This resulted in numerous fire starts over the Bay Area.

Several of these fires eventually became California’s largest wildfires on record. Five of California’s largest wildfires in history occurred in 2020, and four of these (all except the Creek Fire) occurred in August. By the time it was fully contained on November 12. the August Complex alone had scorched 1,032,648 acres, nearly 3.5 times the area of all of Multnomah County.

Here’s a picture of the Doe Fire on August 17, the largest of all of the individual fires within the August Complex.

Doe Fire. The fire was experiencing strong growth at this time, but fire activity was not as extreme as it typically is during the warm and very windy/dry Diablo winds that North/Central California frequently experiences in the autumn. Picture taken at 3:21 pm 8/17/2020.
Credit: US Forest Service

Thunderstorms and extreme heat also made it into the Pacific NW. Dry lightning on 8/16 ignited numerous fires across the Oregon Cascades, including the Beachie Creek and Lionshead fires, both of which would grow dramatically during the Labor Day firestorm. Seattle reached a high of 98 degrees on the 17th, while Portland “only” made it to the mid 90s due to smoke from the California fires reducing high temperatures. I was fishing up at Sekiu during that time and escaped the extreme heat, but I was treated to a spectacular nocturnal lightning show that I blogged about here.

The Labor Day 2020 Fires

While the August 2020 fires were caused by lightning, the Labor Day firestorm was due to extraordinarily strong and dry offshore flow that caused new or existing fires to quickly burn out of control. I still get chills looking at the satellite imagery below.

I wasn’t in Portland at the time of the Labor Day fires; I was staying up on Whidbey Island near Puget Sound with my folks. But I still remember how gusty the east winds were on Labor Day and seeing the whitecaps on Puget Sound, which I’d never seen before during easterly winds. And although the smoke was nowhere near as bad over Whidbey as it was over Portland and the Willamette Valley, it was still extraordinarily thick. The persistent smoke created a temperature inversion at the surface, resulting in a thick, damp smog that stuck around for the better half of a week.

From the relatively little historical analysis I’ve done, it appears to be the most severe event since the 1902 Yacolt Burn, and perhaps even exceeding that. With widespread 40-60 mph wind gusts in the lowlands and ~100 mph gusts at Mt Hood (more specifically, the top of Magic Mile chair at Timberline) for approximately 12 straight hours, the wind speeds in the September 2020 event were far stronger than any other August/September offshore flow event I’m familiar with. The wind alone had a substantial impact to the power grid, with nearly 200,000 PGE customers (approximately 22% of the customer base) out of power during the peak of the storm and approximately 241,000 customer outages in total. The combination of these damaging winds with record-dry fuels, relative humidities in the single digits, and the existing fires from the August 16 dry lightning event (specifically, the Beachie Creek and Lionshead fires) resulted in an event that will hopefully not soon be surpassed. All of the other major fires labeled below were first observed during the Labor Day event.
 
Visible Satellite on 9/28/2020 showing burn scars from the 2020 Labor Day Fires
Credit: CIRA/RAMMB
One of my favorite charts I’ve seen that illustrates how unusually strong the offshore winds were for the Labor Day fires is the scatterplot below showing all recorded speeds/directions at the 925 hPa pressure level (approximately 2,500 feet) in August/September as measured by the weather balloon launched twice daily (00Z and 12Z) at Salem, OR. The measured wind speeds on 12Z (5am PDT) Tuesday 9/8 were about 30% higher than any other “offshore” (i.e. with an easterly component) winds from 1956-2020. It’s one thing to set a record for the strongest offshore winds at a location during peak fire season, and it’s another thing to completely obliterate it. 
The direction and strength of all August-September winds at 925 hPa from 1956 – 2020. Observations were recorded via the weather balloon launches at Salem Int’l Airport. Note how the 12Z 9/8/2020 value is by FAR the strongest offshore wind ever recorded at Salem.
Image created by University of Washington research meteorologist Dave Ovens. Check out his awesome page on the September 2020 wildfires for additional analyses, observations, and archived model runs.

In conclusion, a repeat of September 2020 is highly unlikely but not outside the realm of possibilities, and I’m very concerned about the upcoming offshore flow season (mid/late August until the first wetting rains) for fire danger west of the Cascades due to how dry fuels are, as even a light/moderate event would result in critical fire danger. Practice those wildfire prevention tips and let’s do what we can to reduce the chance of human-caused ignitions.

Charlie

Featured image: Bootleg Fire on 7/14/2021. Credit: Inciweb

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