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Tuesday, October 27, 2020  Spokane, Washington  Est. May 19, 1883
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Weathercatch: Potent upper-level low system erupts over region with uproar

Ominous storm clouds over Colfax, Wash., Sunday afternoon, May 17, 2020, portend a series of thunderstorms unleashed over the Inland Northwest by a dynamic upper-level low pressure system. (Linda Weiford / Courtesy)
Ominous storm clouds over Colfax, Wash., Sunday afternoon, May 17, 2020, portend a series of thunderstorms unleashed over the Inland Northwest by a dynamic upper-level low pressure system. (Linda Weiford / Courtesy)
By Nic Loyd and Linda Weiford For The Spokesman-Review

Unless you were following the National Weather Service-Spokane’s Special Weather Briefings last weekend, it would have seemed unlikely that the Inland Northwest would be slingshot by a powerful storm system Sunday afternoon. At 1:30 p.m., we enjoyed partly sunny skies, temperatures in the mid-60s to low 70s and a light breeze, all accompanied by a chorus of bird songs.

By 2:30 p.m., ominous clouds rolling toward our region made it clear that we were in the path of a potent weather disturbance. Called an upper-level low, it’s a low-pressure weather pattern formed high in the atmosphere – generally between 10,000 and 30,000 feet – filled with a pool of cold air.

Packed with a lot of energy, upper-level lows can generate downpours and thunderstorms, strong winds, temperature drops and even isolated tornadoes. In satellite images, they often appear as pinwheels, similar to hurricanes. But where hurricanes are warm-core systems, upper-level lows are cold-core.

Sunday’s upper-level low approached the Inland Northwest from the southwest, unleashing a series of thunderstorms between 3:30 and 5:30 p.m. Overall, the region saw cooler temperatures, heavy rain, high winds, lightning and thunder. How intense conditions got depended on your location when each storm took a dive.

Spokane, Moscow-Pullman, Colfax and other Eastern Washington and North Idaho towns were in the system’s bull’s-eye. During a mere hour, the temperature in Spokane nosedived from 66 degrees to 54. Sustained winds blew at 29 mph, with gusts at 33 mph. What’s more, a quarter-inch of rain fell during a relatively brief period – needless to say, we got drenched. So much so, that the sudden onslaught of water raised river levels and even triggered a mudslide on U.S. Highway 95 south of Moscow. Also, a lightning bolt struck a locust tree on the playground of a Moscow school.

Most common in springtime, upper-level lows are notorious for taking their sweet time moving on. They can meander, inch along in baby steps, or flat-out stall overhead. Sunday’s system didn’t stall, but it certainly dawdled. The next day, Monday, two “cold air funnel” clouds over the Palouse were reported and photographed by multiple witnesses, according to the NWS-Spokane on Facebook. In addition, cool, wet weather associated with the pressure system persisted well into the week.

If the upper-level low behaves as predicted, it will vanish by this weekend. Afterward, late May warmth and dryness will return.

And may you have a well-deserved, relaxing Memorial Day.

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.

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