Wildfire once burned an estimated 6 million to 13 million acres each year in California

https://www.wired.com/story/west-coast-california-wildfire-infernos/

"the inescapable fact that California is flammable. It is hard for us moderns to accept—conditioned, as we are, by Smokey Bear—but fire is every bit as natural and inevitable in the American West as flooding in the Mississippi River Basin and hurricanes in Florida. Fire is not only guaranteed by climate and ecology; it is vital to the health of many ecosystems."

"wildfire burned an estimated 6 million to 13 million acres each year in California, according to one study, far more than even the current record-­setting season."

"Most of those frequent fires past were different, though, in a critical way: Burning with a shallow flame front, like the early stages of the Carr Fire, they ripped through grass, pine duff, and fallen branches—so-called surface fuels—on the forest floor instead of torching whole trees and leaping crown-to-crown as our biggest fires do today. Those regular surface fires generally kept overall fuel loads so low that each subsequent fire could only do the same—scorch out the understory without harming mature trees."

NASA Fire map with a week of burn intensity history

https://firms2.modaps.eosdis.nasa.gov/map/#t:adv;d:2020-08-14..2020-08-20;l:nrt_viirs=[frp-0..200],firms_static_modis,protected_areas;@-121.5,37.8,9z

Bay Area air quality and smoke map

https://fire.airnow.gov/?lat=37.6907269&lng=-122.05836850000001&zoom=10

Where the wind is going to take the smoke

https://www.windy.com/-Fire-intensity-fires?fires,37.659,-120.336,8

Daily satellite imagery of where the smoke has been going

https://go.nasa.gov/3l4Pg1V

Record-setting high pressure ridge

https://www.washingtonpost.com/weather/2020/09/12/california-wildfires-smoke-plumes/

"Because the air is so warm, it expands, causing the atmosphere to grow in height vertically."

"On Sept. 5, a day after it was first ignited, its smoke plume soared to 55,000 feet. That’s taller than many of the tornadic thunderstorms that roll across Oklahoma and Kansas each spring."

"It’s about a solid 10,000 feet higher than we’re typically seeing with the highest of these plumes."

"we’re beneath a record-setting ridge,” said Lareau, describing the strong high-pressure system that brought the record warmth. Because the air is so warm, it expands, causing the atmosphere to grow in height vertically. “That’s going to have very high tropopause heights,”

Vapor-pressure deficit

https://www.theatlantic.com/science/archive/2020/09/most-important-number-for-the-wests-wildfires-california/616359/

"When the vapor-pressure deficit is high, it means the atmosphere has become an immense, six-mile-high sponge."

"In August, even before the state saw a searing Labor Day heat wave, the vapor-pressure deficit reached its all-time peak in California. "

"Thanks to VPD, every additional amount of warming leads to exponentially more fire than the year before it. This is because VPD measures the absolute saturation of the atmosphere, which increases even if the atmosphere stays just as humid."

Plume-driven Mass Fires

https://www.wired.com/story/west-coast-california-wildfire-infernos/

“These fires aren’t just big because of, say, climate change or some accident. They’re big because we have a landscape full of long-burning heavy fuels, just like cities.”

"the separate convective columns of all those many little fires begin to join into a single, giant plume. As the hot air in that plume rises, something has to replace the air at its base—more air," "pushing temperatures high enough to flip even heavy fuels (giant construction timbers, mature trees) into full-blown flaming combustion. Those heavy fuels then pump still more heat into the convective column, creating a feedback loop:"

"plume(s) reached 18,000 feet, high enough for water vapor, carried aloft, to condense into liquid cloud droplets, spawning a pyrocumulonimbus, or fire-generated rotating thundercloud. That process of condensing hot vapor or steam into liquid releases heat" "this condensation of water vapor into liquid cloud droplets delivers new heat to the plume itself, causing it to rise even faster and higher." "Back down at ground level, meanwhile, the rising plume pulled in new air"

"A classic surface-driven wildfire ignites only the immediate area crossed by the fire’s own shallow flame front; falling firebrands, by contrast, allow plume-driven fires to propagate miles from the core burn, as if launching incendiary bombs to ignite entirely new mass fires"