A true pineapple express for the Pacific Northwest beginning Sunday

The next Pacific Northwest atmospheric river is forecast to impact the region from Sunday through Tuesday, coming in at a category 3 on the atmospheric river scale. This will be a true pineapple express event with the moisture plume originating from Hawaii.

The moisture content isn’t particularly impressive but with this event is forecast to last just short of three days. Snow levels will rise significantly and this combined with moderate rainfall will lead to widespread snowmelt in the Cascades and a possible flood risk, though the flooding won’t reach the level we saw earlier in the season.

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The pineapple express will be driven by a mixture of low pressure in the Gulf of Alaska, high pressure off the California coast, and cold fronts stuck in the middle. Low pressure systems drag cold fronts behind them but the strength of the high pressure to our south will keep them from progressing onward.

The halted progression is what channels the atmospheric river over the Pacific Northwest for several days at a time. Right now modeling suggests the moisture plume will be aimed near Seattle with consistent rain extending to the north of Vancouver and as far south as Salem.

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Moisture will be coming into the Pacific Northwest from due west and the Cascades will stop most of it from reaching into the Columbia Basin. High clouds can be expected for places like the Tri-Cities and Yakima. Temperatures will warm up but precipitation will be minimal.

The B.C. Interior and Coast Range lie to the north of the pineapple express so temperatures won’t be as warm there. That said, with the active storm track in the Gulf of Alaska there will be plenty of precipitation in that region.

Precipitation will likely fall primarily as rain in interior communities like Kamloops and Prince George but the mountains will probably still see a good amount of snowfall. The last couple of weeks have helped to clear the snow deficit in most of British Columbia.

The same can also be said of Northern Washington (including the Okanogan) but this three days of rain is going to wash all of that away. Snowpack remains below average in Washington south of Stevens Pass and critically below average in Oregon.

As noted, the flood threat is not as severe as December 2025 but some moderate flooding can be expected north of White Pass along rivers draining the Cascades, B.C. Coast Range, and Vancouver Island mountains. As of publish time, no flood alerts had been posted in Washington, Oregon, or British Columbia but I expect these will come out over the next day or two.

Beyond Tuesday the California high expands northward, sending the storm track more toward Prince Rupert and Ketchikan and keeping the bulk of the Pacific Northwest dry. More mid-elevation snowmelt can be expected during the second half of next week as temperatures remain warm.

Temperature inversions are common under strong high pressure this time of year and next week will be no different. Despite sunny and relatively warm weather in the mountains, the Columbia Basin will likely see a long-duration inversion develop with low clouds, fog, and steady temperatures in the 30s (around 2ºC).

It remains to be seen just how deep this inversion will get. Some models are hinting at it continuing into the week of the 19th and if that’s the case we’ll probably see it extend to Spokane and Kelowna.

Some inversion activity may also be noted in the Lower Mainland, Puget Sound Region, and Portland metro but this is usually slower to form because of the proximity to the ocean (rather than being completely surrounded by mountains like the Columbia Basin is).

I feel confident in saying that Medford and Eugene will be socked in with inversion clouds during this period. There is less confidence for the larger metro areas west of the Cascades.

The featured image is ECMWF modeled total precipitable water for midday Monday. (WeatherBell)

#BCstorm #orwx #PineappleExpress #wawx #Weather

Since ~4PM today, the #PDX Big Pipe has been at full capacity, dumping raw sewer waste into the Willamette River.

The #PineappleExpress is dumping water on the city.

😳 It's so quiet out...

#CalmBeforeTheStorm
#WAwx #PineappleExpress
🍍🚂

Got wind gusts now and it's... 60° ???

Heard a tree fall a few minutes ago. 😳

🍍🚂 #PineappleExpress
#WAwx

Stay Safe out there! 🫶

Unfortunately my rain gauge seems to be on the fritz... however, reports from weather friends in #PortAlberni are that they are nearing 110mm over the past 24 hours. The Airport measured 42mm for the 14th. I would expect more than that today.

And oh ya, get out the T-Shirts, it's 15ºC! :+)

#BCStorm #AtmospericRiver #PineappleExpress

Yesterday was sunny here but people shouldn't get lax. The ground is so saturated.

LAST NIGHT:

MORE #evacuations in #Auburn & #Kent.

This video was posted 10 hours ago, so around midnight.

#WAwx #PineappleExpress

https://www.instagram.com/reel/DSPI6BnDr0Y/?igsh=ZnJpMWt0cjZxaDE3