December 28, 2015

El Nino: A Weather Force Awakens

El Nino's impact on the West Coast will soon awaken.  And like the Dark Side of the Force, it has planted the seeds of its own demise and a new order will arise next winter.

This year one of the strongest El Nino's of the past 50 years has developed.  A number of studies have shown that the major impacts of strong El Nino are typically not felt over the West Coast until after approximately January 1.  These impacts include wetter than normal conditions over California, a bit drier than normal over the Northwest, reduced snowpack accumulation over the NW mountains, and less chance of lowland snow.

After January 1, El Ninos tend to produce an offshore trough of low pressure (heights) over the NE Pacific and relatively higher pressure (heights) over NE Canada.  The composite below 500 hPa heights (around 18,000 ft) shows the general pattern.  This flow pattern tends to cause the Pacific jet stream to split, with flow going into California (black arrow).

The latest forecast models suggest that exactly this kind of transition is about to occur, with a major circulation shift that will dry out the NW and increase precipitation over California.

Take a look at the flow pattern anomaly (difference from normal) for 500 hPa for 4 PM Sunday (yesterday).  Higher heights than normal over the NE US,  lower heights than normal over the West Coast and higher height over the NE Pacific.  Not very El Nino like.

But here are the forecasts for 5 and 10 days out.  Huge change with low pressure developing over the Pacific.  Shades of El Nino.  A huge ridge over us on Friday in the first map...absolutely dry

Take a look at the total precipitation predicted over the next 2 weeks by the National Weather Service GFS mode.  Substantial precipitation over southern  and northern CA (red colors), but much less  over Washington State and BC.  Very much an El Nino pattern..

The latest Weather Channel ten day forecast for Seattle shows NO PRECIPITATION for over a week.

 And the latest Climate Prediction Center 8-10 day forecast predicts the classic  strong El Nino pattern: dry over the northern tier of states (including the Northwest) and wet over California.

The El Nino force is strong with this one.

But the dynamics of a strong El Nino puts in motion changes that eventually destroys this feature.    The latest central Pacific tropical sea surface temperature index (Nino 3.4) shows that this powerful El Nino has peaked and slowly declining.

And seasonal climate models (like the NOAA/NWS CFSv) indicates a rapid weakening of El Nino during the spring, with substantial confidence.

 But El Nino will remain strong enough the second half of the winter for powerful effects.   Next year will probably be a neutral or La Nina year, but it is too early to tell.

The bottom line:  enjoy your skiing NOW.    You should not expect the second half of the winter to bring bountiful snow like the first.  Our reservoirs are in great shape with huge amounts of December water.  Water managers need to be conservative from now on, saving as much water as possible.  Our huge snow pack (compared to the wimpy one of last year) should ensure that next summer is no repeat of last summer.

2016 Northwest Weather Workshop On March 4-5, 2016

The Northwest Weather Workshop, the big regional meeting on Northwest weather will take place in Seattle on March 4-5, 2016.   At this meeting we talk about the latest advances in understanding our local weather.  It is open to all.   For more information go here.  

If you want to give a presentation, abstracts are due on February 1.


  1. Sounds like I should start planning a February ski trip to Tahoe instead of Whistler.

  2. Dr. Mass, your are very quick to point out that weeks of anomalously high temperatures, strong storms, or acidic waters are well within the range of natural variability and cannot currently be attributed to global warming. Likewise, almost every winter we encounter long stretches of sunny weather and inversions in the mountains, just like is predicted for the next week or so. How can you be so certain that this now can be attributed to the El Nino. and is not just natural variability?

  3. Unknown,
    I can not be absolutely sure, but there is a deep literature and substantial climatological evidence for a major shift around new year for El Nino years and particularly strong El Nino years like this one. The persistence of the changed pattern is further evidence as are the components...the development of the trough/low in exactly the correct place...cliff

  4. We can't know for certain if this upcoming stretch of weather is due to El Nino, but it will be a good example of what the El Nino will look like when it does get here ; ).

  5. Cliff,
    In a future blogpost can you describe in more detail how the El Niño sows the seeds of it's own destruction?
    Thank You,
    Noah Landau

  6. Well here's hoping it's a whopper of a neutral or la Nina next fall/winter. I'm really missing big lowland snow and wind events. Yes, we had some wind this fall, but nothing out of the ordinary.

  7. Ski resorts probably understand that the prolonged dry clear weather is (especially overnight and early morning) is ideal for snow-making. So that's one way the quality of the pistes can be maintained thru this period.

  8. So enjoy skiing now because rain will come in? Or why else would the amount of snow that's already fallen not last through Spring if it's simply going to be dry without much more snow between now and Spring?

  9. Oh, yeah. Dry, sunny and COLD. No one seems to mention those overnight lows and wimpy daytime highs. I'll take a warm rain, any day, over that. Lew

  10. Guess I should forget a late March visit to Whistler...

  11. Is the milder air associated with El Nino ever going to make an appearance? With temperatures like these, the
    bountiful mountain snow won't go anywhere for months. Although you recommend going skiing now, there's no mention of any temperature moderation above. That would be a key factor; is there any expectation of some milder temperatures?

  12. Memories are fickle things, but - I remember winters up here in western Washington during the late 60s and early seventies. It seemed like we could count on a significant snowfall coming at some point during the winter. I also remember giant icicles hanging down from our gutters, and how much it hurt if you broke one and the base came down on your head!

    The working, commuting adult in me doesn't miss that at all... but the kid inside me sure does.

  13. You have to remember, El Niño years setup perfect conditions for inversion layers. Cold at sea level where the weak rays of the sun cannot warm the trapped lower level of the atmosphere and radiational cooling at night lets out what warmth, and then some, during the long nights, but you might find 60 degrees or more at Paradise on Mt. Rainier in the warmer air aloft Some of my best mountain ascents have been in El Niño years needing only t-shirts at 6000'. The snow hardens up, avalanche risks diminish, and there are no bugs.

  14. Cliff, I still remember back when I'd just turned 40, I spent a very sunny January weekend at the Mount Baker ski area (about 5000 feet). There was excellent recently fallen snow and the thermometer was stuck at 7 degrees F. day and night! No inversion. What set of conditions will allow the mountains to be sunny and very cold as opposed to the inversions which I fear El Nino will bring us?

  15. Thanks for the update. It's great to see our current snow pack, but while its above average for December, in a normal year snowpack hits its max in April, and our current snow pack is only 1/2 of the median April peak- so if snowfall drops off now, or melts early, we could be looking at significantly less than average snow pack when it counts for our water supply (April on). There's a nice set of visuals here for those that want to track current snow pack relative to seasonal norms:
    Nice to see that we've already well exceeded last year's total- a reminder what a freaky year it was!

  16. Okay, these are fun- NRCS data to date for snotel sites with probabilities of subsequent snow pack development based on historic record:

  17. Cailean

    Dr. Mass understands skiing. The best skiing is on new powder snow with cold temps at the ski areas, which we have now and which we won't have this weekend when the freezing level rises to above 10'000 ft. AMSL.

  18. Its a good thing forecasting weather is science fiction! So much BS hype!

  19. According to Portland NOAA office:


  20. Has anyone else noticed how displacement of Arctic Air has started in Alaska? Temperatures in the middle of the state are no longer below zero; they are now above freezing. Very odd how Alaska is warming up while the West Coast is getting colder.

  21. NPR said the storms and heavy rains in the Midwest were caused by El Niño. I thought El Niño was a west coast event and is as you describe in your blog. I didn't know it affected the rest of the US and how can it affect elsewhere BEFORE the West Coast? Am thinking NPR is incorrect. Any thoughts on their interpretation?

  22. Cliff, I truly appreciate all of the work you put into your blog and always dig the level of detail you provide. Could you kindly make a blog post about what we can expect to see for temps and precip for WA for the remainder of January? Specifically related to snowfall. Thanks. Or provide me with a link to where I can read about other it from other reliable sources. Many thanks!


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

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