Weathercatch: Why our region’s unusual breed of thunderstorms is dangerous this time of year

Storm chasers don’t come to the Inland Northwest for action. Tornadoes are rare, and the region averages only a dozen or so thunderstorms each summer, most of which are benign. How is it, then, that lightning strikes cause many of our wildfires?

Because these aren’t your run-of-the-mill thunderstorms shooting lightning bolts from the sky. Called dry thunderstorms, they produce lightning and thunder but little or no rain. Any precipitation that falls evaporates before hitting the ground.

Dry thunderstorms occur in locations where the weather has been hot and dry – like this summer in the Inland Northwest. If a tendril of electricity sparks a flame on parched vegetation, there’s no rainfall to extinguish it. On top of that, localized downdrafts can produce “splashes” of wind gusts capable of fanning the flames and scattering embers to create additional fires.

The majority of Washington’s wildfires are ignited by humans, and the remainder by lightning strikes, according to the state Department of Natural Resources. The state’s most destructive fire seasons occurred in 2015, 2020 and 2021, the agency reported, with 2015 being the region’s worst fire season in recorded history. While human activity triggered many of the blazes, so did lightning strikes produced by dry thunderstorms during periods of prolonged hot, dry weather.

You’ll rarely witness this kind of weather phenomenon east of the Rocky Mountains, where lightning is often accompanied by downpours. Mention dry thunderstorms to someone in Minneapolis and you’ll probably get a blank stare. Besides getting more summertime rain, that portion of the country also has higher humidity. Not surprisingly, their wildfires aren’t nearly as large or widespread as they are in the West.

Now that we’re entering the driest time of year, you’re probably feeling the parch. Washington state and North Idaho are on alert for high fire risk all through August and into early fall, according to the National Interagency Fire Center in Boise. Continued heat, low humidity and arid vegetation, combined with human ignitions or dry thunderstorms, elevate the threat. Add wind gusts like those that kicked up on Monday, and the fire threat becomes dangerously high.

Dry thunderstorms pose another hazard besides fires. The lightning they produce can strike people. So keep in mind that no rain falling from an angry storm cloud doesn’t mean an all-clear for being outdoors.

Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek.