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Q&A: How lightning from dry thunderstorms can spark wildfires

Scott Rowe explains how lightning from dry thunderstorms can spark wildfires.
AP Photo
Scott Rowe explains how lightning from dry thunderstorms can spark wildfires.

Isolated mountain thunderstorms aren’t uncommon in the North State this time of year. When they do occur, they can produce hazardous dry lightning that can spark fires. In fact, lightning has caused several massive fires in the region including California’s largest wildfire, the August Complex, which burned more than a million acres across seven northern California counties starting in August 2020. That same month, lightning also sparked the Bear Fire — later known as the North Complex. Three weeks later, the Bear Fire moved through the communities of Berry Creek and Feather Falls, killing 16 people.

To learn more about dry lightning, and its hazards, NSPR’s Ken Devol recently spoke to Scott Rowe, lead meteorologist with the National Weather Service in Sacramento.

This interview has been edited for brevity and clarity.

"About two years ago, we had that large lightning outbreak that did occur in August that caused millions of acres of land to be burned essentially well north of 10,000 cloud-to-ground lightning strikes with that event and sparked upwards of, I believe 100 wildfires."
— Scott Rowe, Lead Meteorologist with the National Weather Service in Sacramento

On how dry lighting differs from other lightning

Dry lightning, or a dry thunderstorm, is essentially a thunderstorm that develops that does not have precipitation making it down to the surface. That's caused by several factors. Most often — at least in California — the cloud base is just so high in the atmosphere, [it] might be 7,000 to 8,000 feet above the surface. And as that precipitation is trying to fall, it just evaporates. There's too much dry air at the low levels in the mid-levels of the atmosphere. So it tries to rain on out, but we just don't see it at the surface. However, the lightning will still make it to the surface. Lightning does not care if it's dry, if it's moist, that will still continue to make it down to the surface. That's why dry lightning is such a big threat to wildfire starts in California.

On the potential for lightning strikes during summer and fall months in the North State 

This time of the year, typically, we would see some afternoon thunderstorms in the mountains. It isn't out of the question that we see these thunderstorms come in late July and early August. As we get deeper into the fall season and we transition from more summer to fall-like weather, we become concerned about offshore winds in Northern California. Those ferocious northerly winds, those northeast winds, we don't really see as much activity in terms of thunderstorms. But they still can happen through about early November.

On what’s considered peak fire season for the National Weather Service 

Fire season in California goes on until we get the first rains of the season. Climatologically, we tend to see some of the biggest fires and most impactful fires in California during the October and November timeframe. But thinking about two years ago, we had that large lightning outbreak that did occur in August that caused millions of acres of land to be burned essentially well north of 10,000 cloud-to-ground lightning strikes with that event and sparked upwards of, I believe, 100 wildfires. Some of them combined to become a massive wildfire complex. So any time between now and until it rains is essentially peak fire season for us.

"If lightning strikes in a forest that is extremely dry, it might be a lot faster to grow, especially if you have wind. If there's no wind, you can have a fire smolder for several days up to a week before it's even detected."
— Scott Rowe, Lead Meteorologist with the National Weather Service in Sacramento

On the time it takes a lightning strike to possibly develop into a fire 

It really just depends on where the lightning strikes are, how receptive those fuels are. If lightning strikes in a forest that is extremely dry, it might be a lot faster to grow, especially if you have wind. If there's no wind, you can have a fire smolder for several days up to a week before it's even detected, especially in some of the backcountry areas.

On the importance of checking the weather for possible lightning events before going outdoors 

The biggest safety tip for folks is if they do have outdoor plans any time of the year — especially in the summer months — to check the weather before going out and about. It's very difficult to get good shelter out in the backcountry or just out hiking. Because really the best place to be is indoors. And if you're outdoors in the middle of nowhere, that may be very difficult to find shelter.

Ken came to NSPR through the back door as a volunteer, doing all the things that volunteers do. Almost nothing – nothing -- in his previous work experience suggests that he would ever be on public radio.