Weathercatch: When rivers in the sky turn from blessings into a curse

Atmospheric rivers. Perhaps you were introduced to that term just this month. After all, they’ve been making headlines since the start of 2023, hammering California with back-to-back storms resulting in torrential rains, widescale flooding and mudslides.

Last week, one of those atmospheric rivers veered north of the Golden State toward the Pacific Northwest, giving Western Washington a good soak before making its way across the Cascade Range and into Eastern Washington. Although the system weakened by the time it arrived here on Jan. 12, it unleashed as much as 1.24 inches of rain in Omak.

The system also delivered blustery conditions and above-average temperatures. The mercury spiked in the upper 40s in Pullman and close to 55 degrees in Lewiston. Almost overnight, winter became a shadow of its former cold and snowy self.

Because atmospheric rivers caused so much destruction in California this month, they might seem like a new meteorological event. And though the term was formally defined less than 15 years ago, the naturally occurring weather phenomenon is nothing new. It’s just that we know a lot more about them due to advancements in satellite imaging, scientific research and computer modeling.

In our part of the world, an atmospheric river is a narrow column of warm, moist air that typically originates in the tropical Pacific Ocean. Carried thousands of miles by strong wind currents, the system dumps rain or snow when it makes landfall on the West Coast.

As we’ve seen in California, these rivers in the sky can cause massive flooding, enormous property damage and even deaths. However, it’s important to note that most atmospheric rivers are weak and cause no damage. What’s more, they deliver a large percentage of annual rain and snowfall to the Western United States, filling reservoirs and bolstering snowpack. They are vital to the region’s water supply.

For a three-week stretch, atmospheric rivers streamed in from the Pacific Ocean at a relentless pace. Why did California bear the brunt of the storms and not Washington and Oregon?

A strong jet stream centered near California steered the parade of atmospheric rivers into that region. Fortunately, the parade ended this week. A final storm blew ashore on Monday and began to wane the next day.

The next time an atmospheric river forms in the tropical Pacific – which is likely to happen this winter or early spring – it could advance toward the Pacific Northwest. If so, keep in mind that these systems are more likely to bring good news than bad.

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.