‘Fire hose of moisture’ brings rain, winds and threat of floods to Pacific Northwest

A powerful atmospheric river is bearing down on the Pacific Northwest with back-to-back storms, bringing rain, gusty winds and unseasonably warm temperatures until Thursday morning.

Fueling the storm system’s intensity is “a monster moisture plume,” atmospheric scientist Cliff Mass of the University of Washington wrote on his weather blog.

“Very concerning,” he added.

The atmospheric river’s energy barreled across the Cascade Range and into Eastern Washington and the Idaho Panhandle on Monday evening. The National Weather Service Spokane advised residents to brace for gusty winds through the night and into early Tuesday morning. Countless outdoor Christmas decorations were tossed about or blown into neighbors’ yards.

Atmospheric rivers – long plumes of water vapor in the sky – are fairly common along the West Coast during winter months. But this one is notable due to “its long duration and high intensity” of water vapor and the winds moving with it, according to research meteorologist Samuel Bartlett of the Center for Western Weather and Water Extremes at the University of California San Diego.

“The fire hose of moisture is aimed directly at the Pacific Northwest,” said Bartlett, who helps track approaching atmospheric rivers and forecasts their intensity.

The long-duration meteorological event was expected to bring flooding, and perhaps downed trees and power outages as a month’s worth of precipitation gets squeezed into just a few days. Parts of coastal Washington and Oregon are already bearing the brunt of the storm system, and hardest-hit locations around mountain passes may get 10 inches of rain by the end of the week, according to the Weather Service. Several rivers are predicted to hit major flood stage, including the Cowlitz, Snoqualmie, Puyallup and Skagit.

The wind surge that was expected to arrive Monday night was part of the storm system’s first wave. The second wave is expected to move into the Inland Northwest Tuesday night, mostly in the form of rain, rain and more rain.

“In this case, with a very strong atmospheric river, there will likely be more precipitation than normal on the east side of the mountains, farther inland over the Pacific Northwest,” Bartlett explained.

Flood watches are in effect for parts of central and southcentral Washington, including the communities of Wenatchee, Leavenworth, Yakima and Ellensburg. In Latah County, Moscow’s Paradise Creek may experience minor flooding “across many streets and impact homes in the flood plain,” according to the NOAA’s National Water Prediction Service, adding that the flood zone includes portions of the University of Idaho campus. (See: water.noaa.gov/gauges/paci1). The creek is expected to reach its highest level on Wednesday, the agency said.

The Center for Western Weather and Water Extreme developed a classification scale for atmospheric rivers in 2017. The current storm system is classified as Category 4, with 5 being the highest. The more robust the system, the more likely it is to barge up and over the mountains and into our region, Bartlett explained, just like what’s occurring this week.

The moisture and wind-packed storm system developed over the Pacific Ocean to the west of Hawaii and traveled upwards of 3,000 miles before making landfall in the Pacific Northwest, he said.

And though it’s intense, many are not.

“Not all atmospheric rivers cause damage,” the NOAA said on its website. “Most are weak systems that often provide beneficial rain or snow that is crucial to the water supply” by filling reservoirs and bolstering the snowpack.

Speaking of snow, the skiing will be great – but only if you’re up high enough. With the atmospheric river funneling warm, tropically based weather into the region (50 degrees is expected in Spokane on Wednesday and 60 degrees in Yakima), snow levels are predicted to fluctuate at 5,000 to 6,000 feet.

“Given the mild temperatures, all but the highest elevations should see mainly rainfall and not snowfall,” said meteorologist Nic Loyd of Yakima. You can stay updated on National Weather Service watches and warnings at weather.gov.