I’m sitting at home, working on a story relating to the conditions I’m experiencing outside my window. It’s just before noon and it is boiling hot. The fans are on in every room, but all this seems to be doing is pushing the hot air and barely cooling it.

This week marked another period of red flag warning weather for parts of Santa Barbara County. The period of “extreme heat” lasted several days.

You wouldn’t be wrong to worry about the next big wildfire occurring on days like this, but, surprisingly, hot summer days like this don’t necessarily produce the worst fire behavior or the biggest or most destructive of them.

Though some of the area’s worst wildfires have occurred in late June and early July — and even as early as the May 5 Jesusita Fire that terrorized Mission Canyon — many of them have occurred in the fall season when you’d expect things would be cooling down.

But the 1971 Romero Fire (October), the 1977 Tea Fire (November) and the 2017 Thomas Fire (December) are examples of how cruel and deadly fire season can be.

The Fire Triangle in Play

Firefighters look at the potential for fire to occur when three factors come into play: oxygen, heat and fuel — the classic fire triangle. Remove any one and you remove the potential for a wildfire to start or spread. But once started, it takes an even more important ingredient to spread, to become more intense and more destructive.

A week ago, a fire near Los Alamos, the Drum Fire, began in some of the most inhospitable conditions possible: steep topography, flashy fuels with the potential to spread up the hillsides rapidly, hot late afternoon temperatures like those we’re experiencing now, and months of time for the sun to bake things out.

Yet by the time I arrived on scene, it was basically close to being contained.

The difference: the lack of wind. Ironically, during the summer months when temperatures can be at their most intense, the winds often aren’t.

In 2007, when the Zaca Fire began in early July, much of its movement over the mountain ridge not too far from Zaca Lake and up Manzana Creek was driven by topography and fuel rather than wind. That remained the case through most of the next two months before it was contained in mid-September.

Heading into the Fall

But conditions that facilitate larger and more destructive fires may be coming as fall sundowner conditions begin to prevail.

We’re now in the beginning of the fall season. The chaparral vegetation and larger dead fuels have endured months of drying, fuel moistures are reaching its seasonal lows, and we’ve endured close to six months of negligible rainfall — the type of conditions that make ignition easier and fires more intense.

In ordinary conditions, living chaparral retains enough moisture to resist ignition. But after a long dry season, its dead twigs and litter become highly receptive to embers, while stressed live shrubs can burn with great intensity.

Invasive annual grasses can fill openings in chaparral. The annual grasses that have grown so quickly in the wetter months along the roadsides and the ground cover beneath the chaparral form the fine, continuous fuels that ignite readily and spread fire rapidly, increasing the chance that a roadside or human-caused ignition can become uncontrollable before the first engines are on scene, the water-dropping helicopters are there or the first retardant is dropped.

When the Wind Begins to Blow

As sundowner winds begin to develop again in the fall months, they add the final ingredient to what is now a fire-receptive environment, bringing warm, dry, gusty air down the Santa Ynez Mountains that serves as the accelerant for the short-lived, high-intensity wildfires that destroy homes and communities along the front country canyons.

What is Fire Weather?

Together, these conditions form what is called “fire weather” — a combination of weather and vegetation conditions that makes a wildfire easier to start, faster to spread, and harder for firefighters to control.

Not heat alone, or sundowner winds or the bone-dry vegetation, but the sum total of many factors, some of which are constants in the fall season, such as the low fuel moisture in much of the chaparral, the ready-to-burn non-native grasses and the higher temperatures. And some, like the sundowner winds, can turn any fall day into a nightmare.

One might think of fire weather as the combination of dry fuel + dry air + high temperatures + wind. One factor alone may not be severe, but together they can allow a small ignition to become a fast-moving wildfire.

Danger Doesn’t End with Summer

The lesson to be reminded is a simple one: Santa Barbara County fire season often extends well beyond summer.

The historical lesson is clear: the first widespread rains — not the end of summer — are often a more meaningful boundary marking the local fire-weather season, as we’ve learned from the 2017 Thomas Fire and 2018 Montecito Debris Flow. We are closer than ever to the time when fire season can be considered a year-long event.

The Final Determiner

Whether that will be the case or not, the conditions that create what we call “fire weather” may be the final determiner of whether fire season is truly year-long — at least for the near term — or may be so in years where there are extended droughts that reduce fuel moistures to the point that the vegetation can burn in the winter months.

Over time, it may be a changing climate that will be the final determiner. The simple message for now is that summer is almost over, but the fire season is not. In some ways the fall months are even more vulnerable to large, destructive wildfires.

Vigilance is always of utmost importance.