Powerful offshore winds, approaching 55 mph in some areas, are predicted to spread from north to south. The threat is sufficiently acute that utilities are weighing whether to shut off power for up to 30 counties and 600,000 customers in northern and central California on Wednesday and Thursday because power lines and equipment can be ignition sources.
Meanwhile, the National Weather Service has issued Red Flag Warnings — the highest alert for weather conditions that can fuel a fast-moving fire — for the mountains and valleys surrounding the San Francisco Bay area beginning Wednesday morning, and for a large region in and around the Sacramento Valley and foothills.
Red Flag Warnings are also expected from Ventura to San Diego on Thursday and Friday.
Despite the accuracy of fire weather forecasts, the public can still be caught unaware and unprepared when there is an immediate threat, like a mandatory evacuation order or an approaching fire. Under the current system, it’s difficult to know when to act and what to do with the forecast lead time. Could that lead time somehow make a difference in escalating wildfire losses?
The National Weather Service is asking similar questions and has been reviewing Red Flag Warnings for a possible update.
Not a warning
An evaluation of the usefulness and efficacy of Red Flag Warnings has taken on a new urgency because they’ve been in place ahead of recent fires, which were nevertheless devastating.
In 2017, the Tubbs Fire swept into Santa Rosa with shocking speed, driven by extreme winds. The Camp Fire last year, California’s deadliest on record, did the same in the town of Paradise.
Both of these events exposed a key limitation of Red Flag Warnings: They do not alert the public when a fire is actually occurring or on the way.
These warnings are all about conditions that promote rapid fire spread, including high winds, very low relative humidity, dry vegetation and dry lightning.
If computer models detect a developing strong fire weather pattern, forecasters can issue a Fire Weather Watch up to four days in advance, and will upgrade to a Red Flag Warning if it looks like relative humidity and sustained wind speed and gusts will cross high-risk thresholds, known as “criteria.” These thresholds are different for each forecast office around the country and vary within the same forecast area across fire weather zones.
The notice then goes out after forecasters look at the dryness of the landscape, by consulting with vegetation experts at land management agencies like the U.S. Forest Service, for example.
A possible revamp
Officially meant for firefighting agencies, Red Flag Warnings have been important for firefighter safety and useful for positioning firefighting resources. But how should the public use them? That’s one of many points under discussion within the National Weather Service.
“Historically, the Red Flag Warning product was solely used by land management agencies,” Robyn Heffernan, the national fire weather science and dissemination meteorologist in Boise, Idaho, said in an email. “Today, media outlets broadcast these warnings and the public is looking for recommended actions.”
Heffernan is part of a national team of fire weather experts who are reviewing Red Flag Warnings and exploring a wide range of options, from new messaging to more sweeping changes, like an actionable weather warning for an existing fire. “It takes many years to reform and improve a warning product, as it has national significance, and is produced in partnership with many federal, state and local agencies,” she said.
Tamara Wall, deputy director of the Western Regional Climate Center, who is co-leading a study of Red Flag Warnings, sees a system ripe for reform and one that could include new products. “A refresh is needed,” she said.
The Red Flag Warning criteria, which evolved separately within each weather office, are designed around wind and humidity but don’t fully incorporate other factors — like vegetation — associated with extreme fires. In the last several years, new and more refined tools have emerged, along with a deeper knowledge of local climatology, that could help pinpoint the highest risk days and locations.
“We’re interested in doing a really rigorous assessment of the most extreme conditions,” Wall said. While the Red Flag product is generally liked by the firefighting and forecasting communities, “we have to reevaluate the conditions in which we use Red Flags so we can really catch people’s attention,” she said.
Even now, forecasters know some days are different, when fires can race into neighborhoods and leave people with little time to evacuate. Those days happen once or twice a year at a given location, sometimes three or four, said Chris Smallcomb, the warning coordination meteorologist at the National Weather Service in Reno. Much of his forecast area lies east of the Sierra’s leeward slopes, a windy and dry region that hits Red Flag criteria often.
“We need to address these particularly dangerous and volatile situations in a new way,” Smallcomb said. “That’s where things are moving.”
The Reno office has borrowed the “Particularly Dangerous Situation” language from the Storm Prediction Center’s tornado watches, reserved for days when the public needs to take notice and possibly take action. They issued one of these in September for expected wind gusts approaching 60 mph:
“Each office is experimenting with hitting the messaging of these really dangerous days,” Smallcomb said. These advances can come from field offices and then, if they work well, spread regionally or nationally.
As part of an incremental reform process, the national fire weather team also has updated messaging for 2019, including “call to action” statements like this one:
A very dangerous and potentially life-threatening fire weather situation exists. High winds, very low relative humidity, and recent record warm temperatures will create weather conditions favorable for a wildfire to spread rapidly.
What to do
What to do ahead of dangerous conditions — and whether there can be an agreed-upon list of actionable instructions — is another issue altogether. A 2017 social science study found that, when fire danger is very high, weather information should be broadcast with brief, consistent messages that focus on evacuation readiness and preparedness.
Here’s a recent example of this kind of messaging for the Red Flag Warning period, which fills the “Set” piece of fire departments’ Ready, Set, Go! protocol: 1) stay alert to weather and wildfire conditions and 2) be ready to leave with little notice.
Yana Valachovic, a forest adviser and county director with the UC Cooperative Extension, thinks specific actions taken in the hours and days before a wildfire could help prevent future disasters.
“We need to get more sophisticated in helping the public understand what the vulnerabilities are and how to prepare,” she said.
Her post-fire investigations of neighborhoods destroyed in California’s 2017 and 2018 firestorms reveal lessons about both wildfire evacuation and home wildfire protection. For example, knowing when to leave, even without an official evacuation order, is crucial during fast-spreading wildfires. That decision requires close monitoring of (and access to) weather and wildfire information. And for last-minute home preparation, if time allows, she said, residents should target the immediate zone around the home — zero to five feet from outside walls and decks— and clear any materials that could ignite in an ember storm.
“I think education is really important, and the alerts are a very good example of where that education needs to happen,” she said.