Paper on Western Ridging

[Black Hole]

I haven't read it yet, but this may be of interest to some of you.

http://advances.sciencemag.org/content/2/4/e1501344

[Guest happ]

The article's focus:

 

Abstract

Recent evidence suggests that changes in atmospheric circulation have altered the probability of extreme climate events in the Northern Hemisphere. We investigate northeastern Pacific atmospheric circulation patterns that have historically (1949–2015) been associated with cool-season (October-May) precipitation and temperature extremes in California. We identify changes in occurrence of atmospheric circulation patterns by measuring the similarity of the cool-season atmospheric configuration that occurred in each year of the 1949–2015 period with the configuration that occurred during each of the five driest, wettest, warmest, and coolest years. Our analysis detects statistically significant changes in the occurrence of atmospheric patterns associated with seasonal precipitation and temperature extremes. We also find a robust increase in the magnitude and subseasonal persistence of the cool-season West Coast ridge, resulting in an amplification of the background state. Changes in both seasonal mean and extreme event configurations appear to be caused by a combination of spatially nonuniform thermal expansion of the atmosphere and reinforcing trends in the pattern of sea level pressure. In particular, both thermal expansion and sea level pressure trends contribute to a notable increase in anomalous northeastern Pacific ridging patterns similar to that observed during the 2012–2015 California drought. Collectively, our empirical findings suggest that the frequency of atmospheric conditions like those during California’s most severely dry and hot years has increased in recent decades, but not necessarily at the expense of patterns associated with extremely wet years.

 

And from Daniel Swain

 

The Rise of the Ridiculously Resilient Ridge

 

Persistent high pressure in recent years led to extreme drought in California

 

Since early 2013, the state of California has been in the grip of an extraordinary multi-year drought. The accumulated precipitation deficit over the course of the ongoing drought is unprecedented in California’s century-long observational record, and when the additional drying effects of record-high temperatures are taken into account, the 2013-2016 event may in fact be the most severe in a millennium. The amount of water stored in the critically important Sierra Nevada snowpack reached its lowest level in over 500 years in 2015, and the loss of groundwater in the state’s aquifers has literally moved mountains. Drought-related impacts—including decreased agricultural and urban water availability, elevated wildfire risk, dramatically increased tree mortality, adverse effects upon riverine and marine ecosystems, and infrastructure damage to roads and pipelines —have been widespread.

Over the past several years, California weather watchers have become well acquainted with the now-infamous “Ridiculously Resilient Ridge” of atmospheric high pressure—the unusually persistent atmospheric anomaly responsible for redirecting winter storms over the Pacific and ultimately bringing record-breaking warmth and dryness to the Golden State. Like a boulder displacing a narrow stream of water, this sluggish atmospheric feature consistently deflected the storm track to the north of California during the typical “rainy season” months of October to May. As a result, much of the state was left high and dry—even during what is typically the wettest time of year.

 

http://www.weatherwest.com/archives/3996

[TT-SEA]

Same phenomenon responsible for what has been a very wet decade in Seattle.    I wonder if the trend will continue or reverse.

[snow_wizard]

I haven't read it yet, but this may be of interest to some of you.

 

http://advances.sciencemag.org/content/2/4/e1501344

 

It's just a snapshot of where we are.  It has little to do with what may happen in coming seasons.

[Front Ranger]

Always a danger to read too much into short term trends...

[Dan the Weatherman]

I think there is a possibility that all the additional pollution and emissions from the recent industrialization of China and Asia may be in some way affecting the weather patterns in the Arctic and North Pacific, that is leading to the drought conditions in CA and much of the western and southwestern region in general. A lot of manufacturing from many parts of the world have been offshored to China and Asia in recent years, beginning in earnest sometime in the 1990's and has been increasing since. It may be that the resulting emissions reached a tipping point in the last few years leading to this recent change in our weather patterns.

 

On the other hand, it is always possible that there more natural causes of this drought as well, or it could be a combination of natural and man-made phenomena.

[snow_wizard]

I think there is a possibility that all the additional pollution and emissions from the recent industrialization of China and Asia may be in some way affecting the weather patterns in the Arctic and North Pacific, that is leading to the drought conditions in CA and much of the western and southwestern region in general. A lot of manufacturing from many parts of the world have been offshored to China and Asia in recent years, beginning in earnest sometime in the 1990's and has been increasing since. It may be that the resulting emissions reached a tipping point in the last few years leading to this recent change in our weather patterns.

 

On the other hand, it is always possible that there more natural causes of this drought as well, or it could be a combination of natural and man-made phenomena.

 

My money is on a big change coming soon.  Patterns can lock in for years and then change pretty much without warning.  Climate change is a continuous process on Earth.

[Dan the Weatherman]

My money is on a big change coming soon.  Patterns can lock in for years and then change pretty much without warning.  Climate change is a continuous process on Earth.

 

I hope you are right. I would hate to see CA and the SW in general suffer from a perpetual drought for the rest of our lives and beyond.

 

Another thing that is really bothering me about this drought is that it is occurring during conditions that are usually very favorable for wet weather in CA and especially Socal, that is a combination of +PDO and +ENSO.

[Black Hole]

My observation in research is that everybody wants "good results." If you study something you have to find something to say about it or pretty quickly your funding dries up. 

Usually these kind of studies need a really long period of record to mean something substantial. It is probably true that the climate in the period they studied shifted to a drier and ridgy pattern, but it could always swing the other way.