December 07, 2025

A Monster Moisture Plume is About to Hit the Pacific Northwest

 The latest satellite imagery is stunning....and concerning.  A huge plume of water vapor, extending thousands of miles to the southwest, is about to hit our region, resulting in massive rainfall and localized flooding.  

Consider the water vapor imagery late this afternoon (below). Green and yellow are the highest values,


Look at a wider view, and you can see this atmospheric river of moisture extends many thousands of miles to the southwest.


We are now close enough in time to the event, and forecast models are similar enough, that we can have great confidence in the forecasts.  

The forecast totals through Wednesday morning are stunning, with over ten inches over the Cascades and coastal mountains. Some locations in SW Washington and NW Oregon will receive 15 inches.

Very concerning.


But it doesn't end there.  The next 24 hours will bring even more, particularly over the southern Cascades.  Major rivers in SW Washington (e.g., the Cowlitz) are going to flood.

Don't take my word for it:  here are the latest predictions from the NOAA NW River Forecast Center:

TEN Rivers are predicted to go into major flood, up from two predicted a few days ago.



Some rivers, like the Collitz, are predicted to approach all-time record levels (black line below).

Stunning.

I am more than surprised that the National Weather Service does not have flood warnings out for drainages in the central and southern Cascades (see below).  They should.





11 comments:

  1. I am shocked as well that the national weather service hasn't issued these warnings as well. Especially with the models pretty much all supporting a major flood event for many of those areas. Thank you Cliff for all that you do.

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    1. Being professional meteorologists, most likely they just forgot.

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    2. The forecast discussions are also not conveying any real sense of urgency or making it explicit that lives and property could be at risk here. I think that should be one of the major sources of value in the discussions during an event like this (along with surfacing issues with forecast confidence, if necessary). Instead, all one really gets is the feeling that the forecaster was loathe to put down their sandwich so they could type with both hands.

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  2. I don’t understand how the backup pages from the river prediction center can be so diff from the main page- example the Collitz one you show will beak at 13+ feet while the backup suggests it’s 10 feet - that is the page showing forecast uncertainty

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  3. Any news on the potential for flooding on the Chehalis River? I haven't seen much of anything about it. As this River has cut I5 more than once in floods that plenty still remember, it seems relevant to any residents wanting to drive to and from Oregon.

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  4. Should we trust their river predictions- the details they provide suggest the probabilities of hitting the predicted crests are lower than what they hoist up as the predicted crest

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  5. Cliff, I live in Randle and have businesses in Packwood. I saw in my forecast up to 12” of rain in 3 days… Packwood is on track for its second highest water mark in its history.

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  6. We have this rain shadow in whatcom County from Vancouver Island. I wonder if the temperature increase of daytime will contribute to some form of rise in the jetstream, right now we're being sheltered.

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  7. Gotta love Western Washington microclimates. Its the same weather system but its either the end of the world or a complete Nothing Burger.

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  8. But why no convergence zone over South Snohomish county (the usual place)?

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