Weathercatch: Eastern Washington’s tall, withering grasses pose a risk with lightning strikes and human-caused sparks

Remember the thunderous booms that bolted many of us from bed in the middle of the night last Wednesday?

We were lucky.

On July 13, the thunderstorms that began rolling through parts of Eastern Washington and North Idaho about 10 p.m. and intensified between 1 a.m. and 3 a.m. produced a barrage of cloud-to-ground lightning strikes. More than 600 such strikes were detected across the region during the five-hour period, according to the National Weather Service Spokane.

This easily could have ignited large swaths of drying field grasses and weeds, resulting in the first wildfires of the season here in the Inland Northwest. Fortunately, that didn’t happen.

Although it’s easy to think that having a wet spring means we’re at a decreased risk of wildfires this summer, the rains actually heightened the risk in some locations.

For many people, the term “wildfire” spurs images of flaming forests, but east of the Cascades we’ve got lots of grasslands and grass fields. And thanks to the infusion of rain, particularly during early June, the grasses and weeds proliferated.

Then, as July’s temperatures rose, the heat caused them to dry out. Cheatgrass, in particular, grew tall and widespread, and turned quickly from blankets of green into gold-colored tinder. Cheatgrass ignites easier than other vegetation and also burns more intensely.

Why didn’t that happen during last Wednesday’s lightning strikes? After all, not only was there plenty of fuel and multiple opportunities for ignition, but there was wind, which aids combustion by increasing the supply of oxygen.

First, the late-night storm system produced rainfall, as opposed to a dry thunderstorm where the rain evaporates before hitting the ground.

Granted, it wasn’t loads of rain (0.04 inches in Spokane, a trace in Pullman and 0.03 inches in Bonners Ferry), but it was enough to dampen the vegetation. Also, relative humidity, or the amount of water vapor in the air, helps provide a moisture barrier against fire. During those nighttime hours, it measured at values of around 60% .

Had the thunderstorm arrived during the day when temperatures are hotter, the relative humidity level would have been lower and provided less protection.

Keep in mind that as we move deeper into summer, the atmosphere will become drier, as will the abundant grasses and weeds. The season’s first red flag warnings were issued last week in Yakima and the Tri-Cities areas due to high fire danger, and we should expect more warnings in our region.

Whether it’s an ignition spark from a lightning bolt, an ember from a tossed cigarette, a firecracker or an abandoned campfire, given all the fuel that’s blanketing parts of the Inland Northwest, the wildfire risk will go up. Temperatures are expected to soar Tuesday through Thursday of next week. Although we can’t control lightning strikes, we can control human-caused ignitions. Please use caution.

Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek. Contact: ldweiford@gmail.com.