Pineapple Express heads toward the Pacific Northwest next week
A fresh atmospheric river, classified as AR-4, is forecast to drop another 5 to 10 inches of rain across western Washington starting Monday. After a brief lull this weekend, the region will once again face a powerful storm system. The Pineapple Express—a moisture plume that originates near Hawaii—is expected to arrive Monday and could push rivers that are still high back toward flood stage.
“By Sunday and especially Monday, we’ll see rain coverage ramp up again,” said Max Tsaparis, a NewsNation meteorologist, during Seattle’s Morning News on KIRO Newsradio Friday morning. “We’re returning to an atmospheric river level-four scenario for much of coastal Washington through Monday and Tuesday.”
This incoming event carries the same AR-4 rating as the river that broke flood records this week. The Skagit River near Mount Vernon reached 41.54 feet early Friday, surpassing the old record of 41.18 feet set in November 1990. The Snohomish River topped out at 34.1 feet on Thursday, exceeding its 1990 record of 33.5 feet.
What exactly is a Pineapple Express?
You’ve likely heard the terms atmospheric river and Pineapple Express used interchangeably this week. Here’s the distinction: an atmospheric river is a long, narrow stream of moisture flowing through the atmosphere, often stretching thousands of miles from tropical regions toward the Pacific Northwest. A Pineapple Express is a specific type of atmospheric river that originates near Hawaii.
“Atmospheric river and Pineapple Express are essentially the same thing; it’s just about where the moisture starts,” Tsaparis explained. “But tropical moisture into the Pacific Northwest is essentially a recipe for trouble, as we’re witnessing.”
This week’s storm drew moisture from well beyond Hawaii, reaching toward Asia. The upcoming system will align with the classic Pineapple Express pattern, bringing warm, moist air directly from the Hawaiian islands.
Next week’s storm may be less destructive than this week’s event, but river flooding remains a possibility
The hopeful news: next week’s Pineapple Express is not expected to cause the same level of damage as this week. The main difference is duration.
“It won’t be as extreme because, unlike this week when rain persisted on and off since Sunday, next week’s rainfall should be concentrated over just a couple of days,” Tsaparis noted.
Forecasted rainfall totals in the hardest-hit zones are around 5 to 10 inches, compared with the 15 to 20 inches that drenched parts of the Olympic and Cascade ranges this week. Even so, that amount is more than enough to challenge rivers that have only recently started to fall.
“The takeaway is that rivers could rise again,” Tsaparis said. “If you live in a flood-prone area, heed evacuation orders when they’re issued, and even as a precaution, consider leaving before orders go out.”
Warm temperatures amplify the flood risk
A contributing factor is the unusually warm weather. Widespread warm conditions across the western United States have caused precipitation to fall as rain rather than snow, even at higher elevations.
“If it were colder, we’d be talking about more snow in the foothills and higher elevations, which would act like a sponge, holding water until spring,” Tsaparis explained. “But with the warmth, that snowpack is melting away, and the moisture goes straight into rivers.”
Beyond the far peaks where snow still falls, the rest of the region is dealing with rapid runoff, turning most precipitation into liquid floodwaters rather than stored snow.
Understanding the atmospheric river scale
The AR scale ranks atmospheric rivers from 1 to 5 based on intensity and potential impact. This framework is relatively new, used mainly in the last couple of years to help the public gauge risk in a hurricane-like framework.
“Level 4 out of 5 is quite intense,” Tsaparis remarked.
The rating combines moisture content, wind, and duration over a given area. This week’s AR-4 lingered over parts of the region long enough to cause severe flooding. The upcoming AR-4 is expected to move through more quickly, even though it remains highly potent on paper.
What to anticipate this weekend and beyond
Saturday should be mostly dry for western Washington, giving rivers a chance to fall and giving residents a moment to assess damages. Clouds will return Sunday with scattered showers, followed by heavy rain Monday and Tuesday.
After this Pineapple Express moves through, the system is expected to shift south, becoming more of a regional Oregon/Northern California concern as Christmas approaches.
But a prolonged dry spell for western Washington remains unlikely.
“This atmospheric river setup isn’t going away,” Tsaparis said. “The question is who bears the brunt of the next heavy rainfall.”
For more updates, follow Charlie Harger on Seattle’s Morning News on KIRO Newsradio, and check the latest reports and commentaries. You can find more of his work and contact details at the provided links.
