What does it take for fire season to start in NorCal?

So wildfire season is finally starting to take off in Northern California. Here is a thread on why it has taken this long, and what it takes for us to have large fires in California:

California has so many fire suppression resources it is hard for fires to escape initial attack unless at least one of these criteria is met:

  • Multiple starts across a wide area
  • Above average winds
  • Topographic alignment
  • Extreme temperatures
  • Poor visibility for aircraft

Massive airpower for firefighting in Ca. means an individual fire can have half a dozen air tankers on it within the first hour. There are heavy helicopters stationed all over the state, too, and these are extremely effective on initial attack if they can refill nearby.

The aerial response starts to break down once we have multiple ignitions, especially if some of them threaten areas with significant population. Urban areas are higher priority for drops. Heavy airtankers are national assets, and can be diverted to new starts in other states.

Winds, especially when coupled with rough topography, can help a fire which starts in the right place grow extremely quickly. This can be problematic, because at some point, there just aren’t enough resources to put out the amount of fire which is now on the ground.

If a fire runs 3-4,000 acres in the first afternoon, it might have over 10 miles of perimeter. If the land is inaccessible to bulldozers, you might need a dozen hand crews to cut line around the fire, which is growing by the hour.

Once all of the hand crews in your region are committed, or even if you just get half of the ones you order, your fire can start to outflank the limited number of firefighters you have at your disposal. Some fires are not directly fightable by ground crews.

In rugged terrain, fire engines have limited utility. They can support hose lays along firelines cut by hand crews, or support firing operations, but by themselves they rarely stop a fire on steep inaccessible ground. We have lots of engines. They are rarely the weak link.

Heat exhaustion is a real thing. Once the temperatures are over 100F, it is really difficult for ground firefighters to sustain intense physical activity for very long, and people start to go down. This can be a real issue in places where bulldozers can’t get access.

Aircraft are very effective on initial attack in fuels where long-range spotting is not an issue. When fires take off in timber and start casting embers long distances, aircraft lose utility. Without people on the ground to follow up, retardant just slows a fire’s spread.

If a fire is not controlled in the first day or so, we go into ‘extended attack’. Even on these fires, the number of hand crews and other resources available in Ca. means we can often wrap a fire which has made a rapid, terrain-driven run and stalled at the top of a ridge.

So we start to see bigger fires when we have: extended periods of high heat, multiple fires starting at the same time, winds which move fires faster than tankers and ground forces can keep up, or smokey skies which take away our access to aircraft.

Minimum nighttime temperatures are higher now than they were 30 years ago. In the past, it was more common for fires to ‘lay down’ at night, and much of the most effective firefighting took place then. Many fires burn hotter at night now, and they’re harder to catch.

We haven’t talked about dry lightning busts, yet. These can start thousands of fires, and within a day to two, they make enough smoke to shut down helicopters and fixed-wing firefighting. These fires get triaged, and the ones threatening towns get high priority.

Dry lightning busts happen at least once a decade in NorCal. Some busts are confined to a County or two. Others hit the whole Northstate. Significant lightning dates in my career have been 1999, 2008, 2014, and 2020. Many of the acres burned by these fires were low-severity.

So what puts out big fires?

  • Big firing operations
  • Winter
  • They run out of topography, hit the desert or ocean, or burn into another recent fire.

If a fire is 100,000 acres, still has fuel available and the weather stays dry, we almost never are going to be able to put it out.

I’m ramping up The Lookout for another season for reporting. We don’t spend much time on small fires, and focus more on large ones where we can dig deeper into the tactics and talk about what we think is interesting about them. Thanks for your support!

Taking advantage of a slow June fire season to prescribed burn in Chico, California.