The city of Berkeley and the Berkeley Fire Department are taking a new and aggressive step in addressing fire season, and residents of the Berkeley hills — and by extension, the Oakland hills — are being told they should preemptively evacuate under certain circumstances.

Berkeley is preparing its hillside residents for the reality that fire is going to present an imminent threat for a few days out of every year from now on. And rather than see a repeat of the disastrous 1991 Oakland hills firestorm in which killed 25 people and destroyed 1,300 homes, officials are hoping to reduce the loss of life if a similar wind-driven fire were to happen again.

“During 'Extreme Fire Weather' — rare periods of extremely low humidity and high winds defined by Berkeley Fire Department — residents living in hillside fire zones are advised to make plans to stay elsewhere," the city said in a statement issued to residents Tuesday.

The fire department also put out a chart and the YouTube video seen below explaining how Extreme Fire Weather occurs potentially during Red Flag Warnings, but not all Red Flag periods constitute the extremes they're talking about.

The department has defined three fire zones in the city: Zone 1, the flatlands, has some fire risk from wind-driven fires, but is the least at risk; Zones 2 and 3 in the hills, are at highest risk, with Zone 3 being a small area of especially high risk around the Fire Trails, east of Piedmont Avenue just above the Cal campus.

"Fire Zones 2 and 3 in the Berkeley hills are at the greatest risk, given the mountain topography, dense vegetation, and narrow, winding roads," says Berkeley Fire Department Special Operations Chief Keith May in the video. "All of these are challenges for fire response apparatus to navigate in the best of times. When these roadways are packed with cars and people trying to escape a fire, it will be really difficult for us to get responders up into the hills to fight the fire."

May goes on to explain the phenomenon of the Diablo Winds, and what triggers Red Flag Warnings, and says that Berkeley is taking things a step further and identifying the days of most intense wind and low humidity that it is deeming "Extreme Fire Weather." There were two such "extreme" days in 2020, and the chart they've created shows how all of the worst and deadliest wildfires in our region in recent years happened on these days.

The Oakland hills firestorm and the 2018 Tubbs Fire, for instance, began on days when relative humidity was between 2% and 7%, with sustained winds over 40 miles per hour.

"This illustrates why we want you to leave the Berkeley hills during Extreme Fire Weather," May says.

The city is now, for the first time, advising residents to leave there homes and stay somewhere else when these conditions occur — and not to wait until a fire is present to evacuate. The advisory crystallizes some long-held anxiety about these winding-road neighborhoods where the likelihood of people becoming trapped — like in Paradise — during a swiftly moving fire is high.

Residents of the adjacent Oakland hills neighborhoods should probably heed the warning too, even though Oakland's fire department may not issue the same dire message. Those roads aren't any better.