February 04, 2015

Triple Atmospheric River Event to Hit the West Coast

Probably the most significant West Coast heavy rain event of the winter will occur during the next few days, with Northern California being the hardest hit.  Three "atmospheric rivers" will strike the coast between now and Sunday, with the middle one possibly being the strongest in years.

A microwave satellite image taken around noon today shows the first (and weakest) atmospheric river of the three.  This graphic shows the total amount of water vapor in the column, or more exactly what depth of precipitation it could form.  Atmospheric rivers are narrow but long currents of moisture and warmth, with roots in the tropics and subtropics.

The forecast for 1 AM tonight shows this moisture plume reaching the Northwest coast.

The second, and far stronger atmospheric river, is apparent on Friday at 10 AM. The blue values are very large.  This system will bring very heavy rain to northern California.  Why does the moisture plume end quickly at the coast?   Because much of the moisture is forced to condense out by regional mountains.

And then a third atmospheric river, and a very broad one at that, is seen early Sunday.

The model forecasts are quite stable for the heavy rain;  here is the WRF forecast the next 72 hours.   Amazing totals over California, reaching over 10 inches. The Washington mountains get nearly as much!

But the rain does not stop there.  Below is the next 72 hour. A bit less, still heavy 
over Northern California.  This is enough water to bring flooding, and the CA/Nevada river forecast center  is going for significant flooding (see graph, red dots indicate flooding conditions)

The Pacific Northwest Weather Workshop

Interested in attending the big local weather workshop of the region?  The Pacific Northwest Weather Workshop will be held in Seattle at the NOAA facility on February 27-28th.   Everyone is invited and the majority of talks are accessible to laypeople.  To attend you have to register or they won't let you in the gate.  There will be a major session on the Oso landslide.  There is a registration fee that covers refreshments and food, and special student pricing.  If interested, check out this website.

Climate Change and the Pacific Northwest

I will be giving a provocative talk on this subject on March 11th at 7:30 PM Kane Hall on the UW campus in Seattle.  Sponsored by local public radio station KPLU, tickets for this event can be secured at this web site.


  1. Cliff - what is stopping the mass of frigid cold air north of the BC, Fraser River sinking down into Washington to turn this winters precipitation from rain into snow?

  2. This is falling as Rain in Washingtons mountains

    this is not good


  3. Wow ... nice weather blog. I'm in NorCal ... looks like we're going to get some much-needed moisture.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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