Weathercatch: Four years ago, a rare and intense thunderstorm jarred the Inland Northwest
A series of isolated thunderstorms that blew through the Inland Northwest early last week sparked some excitement, even though they weren’t severe. We don’t experience many thunderous booms with downpours and lightning flashes in our region, so they tend to be exhilarating when they show up.
Where some parts of the country get a thunderstorm almost every day during summer, the Spokane area gets an average of 11 all season long. Most are short-lived and cause little or no damage. But every now and then we experience an intense outburst. Take, for instance, the unusual storm system that swept through Eastern Washington and North Idaho four years ago this week.
On the evening of July 23, 2019, a line of thunderstorms rattled the region with strong winds, heavy rains and lightning strikes that lit up the skies, split trees in half, struck power lines and ignited fires. The National Weather Service reported 3,499 lightning strikes that hit the ground. One Spokane resident saw two different trees get struck by lightning in his neighborhood. “It was like, Boom! Boom!” he told The Spokesman Review.
By midnight, lightning strikes were blamed for starting 20 fires in Spokane County, including brush and structure fires. Wind gusts of 60 mph snapped tree branches that took down power lines, contributing to outages among nearly 30,000 customers in the Inland Northwest. West of Spokane. Heavy downpours caused flash flooding and debris flows in the towns of Grand Coulee and Chelan, along with mudslides along US-2 near Waterville.
Needless to say, it was a busy night for firefighters, police, power crews and road workers.
The cause of this wild show was the convergence of abundant moisture, atmospheric instability and a lifting mechanism to force the unstable air upwards. The combination frequently occurs in the Southeast and the Great Plains, but not here in the Inland Northwest. Why is that?
We’re missing a key ingredient here – humidity, or a sizable amount of water vapor in the lower level of the atmosphere. Unlike the warm Gulf of Mexico, the air blowing off the Pacific Ocean into Washington state is cool. Cooler air near the ground is less likely to lift upward to produce thunderclouds. Furthermore, because cooler air holds less moisture than warm air, there’s less fuel in our atmosphere to activate storms.
But on the evening of July 23, 2019, the right conditions aligned to produce a powerful storm system. Hot temperatures at ground level collided with a trough, or upper-level low, that caused much cooler air aloft. This hot-cool temperature juxtaposition created an unstable air mass that was forced upward to cloud level. At the same time, a hefty shot of moist air flowed in from the south. And finally, an abnormally strong jet stream approached the region, carrying more energy with it.
The resulting storm system was dazzling and destructive. In our corner of the world, it was also rare. Lucky for us.
Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek.