January 29, 2018

It never rains in California?

There is a well-known song about it never raining in southern California and during the next ten days folks might give that music a listen.  Why?  Because it won't be raining there any time soon.

Here is the NOAA/NWS GFS accumulated precipitation for the next tens days.
Washington get plenty, as does northern Oregon.  But virtually nothing over California, Nevada, and Arizona.

OK...that is only one run.  What about the 21 member ensemble of forecasts (called GEFS)?  Here they are in what is called a plume diagram....none of the members show rain!

So what is going on?   

A persistent area of high pressure will develop over and and west of California.

For example, here is the upper level (500 hPa) forecast for 10 PM Friday.   Nice ridge west of California, but not enough amplitude to keep the Northwest out of clouds and some rain (this is known as a dirty ridge by local meteorologists).

And here is the average anomaly from normal of the 21 ensemble forecasts for the same level, but for the 240 hr forecast---unbelievable, a big ridge over the western U.S. (red and orange show above average heights)

Mama Mia! This is one persistent ridge!  Not good for skiers in the Sierra, who have enjoyed substantial new snow during the last week.

Now some folks are claiming that such persistent high pressure areas have become more frequent or persistent in the West.  Some even have a name for it:
the Ridiculously Resilient Ridge (RRR).   And a few individuals are claiming that it is due to global warming.  OK, let's check out their claims:  is such a feature becoming more frequent or intense?

So what I did was to go to the wonderful NOAA ESRL web site and examined the average 500 hPa heights (same level as above) over the western U.S. (see the region selected below) for the last 70 years.
Below is the long-time series of the 500 hPa heights for November through February.   Quite a bit of ridging (high pressure) during the 2015-2016 winter, but little trend since the mid-1970s, when there was a major switch in sign of the Pacific Decadal Oscillation (the dominant mode of long-term natural variability over the eastern Pacific).
What about near-surface trends?  Here is the time series for 1000 hPa heights for November to February (essentially the same as sea level pressure).  No long-term trend.

You can do this exercise for different West Coast regions or seasons and you get the same answer (I have tried many combinations)....there is no long-term trend in West Coast high pressure during the past half century. 

We have an anomaly the next few weeks, but there is no reason to expect that is represents  a persistent feature of our future.


  1. So do we really experience more 'atmospheric rivers' in the north west than we did 10-15 years ago?
    Heard that claim on the radio today, caused by global warming of course.

  2. Oh now you gone and done it.
    The AGW crowd will be on here soon and posting to reddit, howling that you are a climate denier, all the while they will continue to miss the point you have made about trends.

  3. Curious to know if this ridge will effect swell hitting the coast? Escaping the atmospheric rivers for a bit and headed to san diego to work...really just hoping to find surf. thanks!

  4. I always enjoyed your articles on California weather; now even more so since I sold my house in Seattle and moved to the Central California coast in December. The realtor in Arroyo Grande, CA. told me this is paradise. She wasn't lying.

  5. I am soooo ready for a Ridiculously Resistant Ridge right about now, especially after yesterday's soggy darkness!

  6. To Rod... we almost located there when we retired. The area from Arroyo Grande up to SLO came in number two compared to Sequim, mostly due to concerns over overall CA water sustainability and overpopulation and our desire to cruise the waterways up to Alaska in our boat, but the climate is classified the same (Csb) with exactly the same annual rainfall as Sequim (about 17"), albeit a bit warmer, especially in winter. Enough weather comes ashore there to make it interesting.

    But around this time of year, I think we got it wrong. But from March to the end of October, we think we got it right. Couldn't stand northern or southern CA, but the middle around SLO is a great option.

  7. "Now some folks are claiming that such persistent high pressure areas have become more frequent or persistent in the West. Some even have a name for it: the Ridiculously Resilient Ridge (RRR)."

    "Some folks" have their own weather blog, www.weatherwest.com. "Some folks" have published their findings in the peer review literature. "Some folks" have shown that "1) Atmospheric pressure patterns similar to the Triple R are now occurring more frequently than they did in previous decades http://advances.sciencemag.org/content/2/4/e1501344.full 2)the unprecedented magnitude and persistence of recent West Coast ridging can be traced (at least in part) to regionally-accentuated warming of the lower atmosphere. http://advances.sciencemag.org/content/2/4/e1501344.full"

    More recently "some folks" have shown that "there has indeed been an increase in the number of days each winter characterized by simultaneously very warm temperatures across the American West and very cold temperatures across the East." http://onlinelibrary.wiley.com/doi/10.1002/2016JD025116/full

    In another recent paper, "some folks" have found "strong relationships between Pacific Ocean temperatures and persistent West Coast ridges conducive to dry conditions in California." http://onlinelibrary.wiley.com/doi/10.1002/2017JD026575/full

    "Some folks" are not sniping at other researchers without actually mentioning to or linking to their work. "Some folks" are not simply eyeballing whether the mean has shifted. "Some folks" might tell you that claiming there is no trend in the mean is a red herring when we are speaking of extremes. If the mean is stationary, but variance is not we can have more intense extremes. If the mean is stationary, but autocorrelation is not we can have more persistent patterns.

    Some folks, meaning you, Cliff Mass, should not pretend to be an authority on the science without actually giving their audience a wider picture of the full debate.

  8. Dr. Mass, have you read the research by Daniel Swain et. al.? They have studied the increasing frequency of west coast ridges, especially during winter. You may find their research results interesting given that they show a distinct upward trend in anomalous wintertime ridging over the west coast.

  9. Nolan...yes...I have read Swain's work. Clearly, I have issues with their approach and findings. Well, that is science. There can be differences that will be worked out over time...cliff

  10. Spring in February and back to winter in March is pretty typical of the NW. I wonder if there is real statistical trend there. Ridges seem common in February, while cold lows seems to plague March and to a lesser extent April. Just my imagination?

  11. Cliff, may I ask what issues you have with their approach? I'm simply curious. Thank you.

  12. I also see a trend in your first graph. And given how finnicky the climate already was with moisture in California, it won't take much to make their water situation worse, especially with increased heat also taking its toll on the sierra snowpack.

  13. I have lived here in the northwest for 25 years and don't ever remember it being this ridgey as in the last 5 years. I don't need some study to tell me what I have seen with my own eyes

  14. Cliff, if you have "issues" with peer-reviewed methods and findings, then why don't you submit a comment to the journals where this work is published?

    For example, if you follow the link to this paper: http://advances.sciencemag.org/content/2/4/e1501344.full, you will find the option to submit an eLetter as a response to their findings. This is a forum for you to publicly critique their methods and findings while also a) giving the authors an opportunity to respond, and b) opening your own critique up to peer-review. That is science. Blog sniping is just rhetoric.

    Somehow I have a feeling that the method "I just eyeballed this one plot of pressure readings and didn't see a trend if I discount all the data before 1970, which I did because of PDO" may not be so convincing to a technical audience.

    Don't get me wrong, I love science blogs. Andrew Gelman's is a favorite of mine. But when he criticizes others, he links to the work, states his reasons, and is open to giving the authors an opportunity to respond. You have not. You simply call out "some folks" and snidely dismiss them.

  15. I think anyone should be able to see the key problem for the layman of climate in this post and following comments:

    How is the incompetent ( the average citizen and the vast majority of the viewers of this blog) expected to discern what is probably correct by sorting the inevitable conflicting opinions of experts?

    Of course we all have our favourites, those that somehow we have developed some sort of affinity for but is that any indication of "most probable" in the absence of any reliable skill in validating the actual science that is displayed before us?

    Maybe that might be a worthy subject to examine unless of course no one actually gives a damn about what is most probable, preferring instead what is most appealing

  16. My my accounting perspective, I can just say the economic costs of 5 more years like the last five would be enormous.

    Agriculture in California would need to make major changes.

    So, with the stakes so high, a full spectrum analysis is greatly appreciated.

    We can't afford to be wrong as the window to make changes will narrow with time.


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

Substantial Snow Returning to the Pacific Northwest

During even the strongest El Nino years there is often a period at the tail end of winter when the atmospheric circulation associated with E...