The Pacific Northwest got drenched and wind-whipped recently, courtesy of the first atmospheric river to hit the region this decade.
And what a doozy it was. This so-called river in the sky was strong enough to earn a rating of 4 out of 5 as it approached the Washington coast. The five-category scale, similar to scales that gauge hurricanes and tornadoes, has been in effect for less than a year.
Washington state and southwest British Columbia bore the brunt of the massive plume of moisture that originated near Hawaii and traveled over the Pacific Ocean until encountering land a thousand miles away. Not only did the atmospheric river funnel pounding rain and strong winds, but it also delivered warmer-than-average temperatures.
Most impacted was Western Washington, where downpours turned parks into ponds and triggered moderate to major river flooding in Puget Sound. Water over roadways led to numerous road closures and a landslide closed the northbound lanes of I-5 near Bellingham for eight hours.
As the system tracked eastward over the Cascade Range, it lost some of its intensity, but still packed a punch. Rain moved in Jan. 29, however, most notable were the strong winds that whipped across the Inland Northwest on Saturday, snapping trees and downing power lines across the Spokane area and North Idaho. In Spokane, sustained winds peaked at 41 mph, with gusts up to 52 mph. Though only a trace of rain fell on the Lilac City that day, short-lived downpours pelted other communities, including Moscow-Pullman, Colfax and Walla Walla.
The atmospheric river also revved up temperatures to about 15 degrees above normal in our region, reaching a high of 54 degrees at Spokane International Airport on Friday.
This fire hose of moist airflow that barreled its way from the tropical Pacific to Washington’s coast was rated 4 on a scale of 5 as it made landfall at Grays Harbor.
In the past decade, scientists learned enough about atmospheric rivers to develop this five category scale to classify each one’s strength and potential impact as it heads toward land. Most of these systems are weak to moderate and produce beneficial rain that helps keep our water reserves full. Others – similar to the one we just experienced – are more powerful, causing intense rainfall, floods, mudslides and wind.
A level 1 is categorized as weak and primarily beneficial. On the opposite end is level 5, rated as exceptional and hazardous.
Our recently departed level 4? Extreme, according to the Center for Western Weather and Water Extremes, which developed the 5-point scale that officially went into use almost a year ago.
This means the first atmospheric river to hit Washington state in the new decade was mostly hazardous, but fortunately, it was also beneficial.
Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek. Contact: firstname.lastname@example.org.
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