Why Dry? The Reason California has Drought

Jan 29, 2016
Hot and Cold Temperatures


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It’s called the PDO, the long-term weather pattern sucking the Golden State dry.

Think of it as the Pretty Dry Oscillation – the Pacific Decadal Oscillation. The official name means Pacific (a Pacific Ocean pattern) Decadal (it lasts more than 10 years) Oscillation (it goes back and forth). It is why California is stuck in a drought.

It’s as simple as hot and cold.

Hot air holds more moisture than dry air. Just think of how steamy and sticky the air can feel during a heat wave.

The Pacific Ocean provides moisture for California and the West. When the waters off the West Coast are warm, they heat and moisten air overhead. The prevailing westerly winds blow the ocean air inland and it rains and snows over the cooler lands, particularly over the mountains. When the ocean is cool, the overhead air is cooler and drier.

(Left) The Positive PDO kept the waters off the West Coast warm. (Right) Since 1999, the Negative PDO usually keeps the waters cooler. Source: Browning Newsletter

There is a 50-to-60-year weather pattern, the PDO that determines how hot or cold the West Coast water is. This Pacific Decadal Oscillation used to be positive, keeping the waters relatively warm from 1976 to 1999. Since then, the waters have usually been cooler. This means the ocean airs bring very little moisture inland.

Since 2012, the situation has gotten very bad. Over 80% of California is in drought and there is almost no snow on Southwestern mountains. Nearly 70% of the water California uses comes from melted snow.

No wonder the Governor of California declared a drought emergency. He is listening to weather experts warning him that the next few months may be as dry as this January!

Compare how much snow there was last winter compared to now! Source: NASA

The negative PDO is a trend that usually lasts for 25 to 30 years. Even when the drought ends, the state will be drier than it used to be. Californians are going to have to conserve their water.

There is some good news. Pacific experts are warning that there is a good chance this year will see the arrival of an El Niño by autumn. El Niños usually bring glorious rain and snow to the West. Hang in there, California!

About This Blog

Are you a weather watcher? Welcome to "Weather Whispers" by James Garriss and until recently, Evelyn Browning Garriss. With expertise and humor, this column covers everything weather—from weather forecasts to WHY extreme weather happens to ways that weather affects your life from farming to your grocery bill. Enjoy weather facts, folklore, and fun!

With heavy hearts, we share the news that historical climatologist and immensely entertaining Almanac contributor Evelyn Browning Garriss passed away in late June 2017. Evelyn shared her lifetime of weather knowledge with Almanac editors and readers, explaining weather phenomena in conversation and expounding on topics in articles for the print edition of The Old Farmer’s Almanac as well as in these blog posts. We were honored to know and work with her as her time allowed, which is to say when she was not giving lectures to, writing articles for, and consulting with scientists, academia, investors, and government agencies around the world. She will be greatly missed by the Almanac staff and readers.

Reader Comments

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The Almanac has historically

The Almanac has historically been very accurate with weather predictions. But to place blame on the staff for the lack of rain is crazy and I personally feel no apologies are necessary.

The Almanac offers weather PREDICTIONS. Information is gathered from multiple sources and then what is offered is (let's face it) and educated guess. Not a certainty, but a possibility.

Please continue with what I consider to be excellent predictions. California is at this moment in the midst of a great storm, so I don't think your Jan-Feb precipitation prediction was wrong, just a few weeks late!

Thank you. The Almanac staff

Thank you. The Almanac staff historically has done a great job. They give the best probabilities.

This current storm won't end the drought but it will offer some much needed relief.

Why are you not warning your

Why are you not warning your subcribers to the influence of weather by the gross dumping of heavy metals and other particulates by jets through GeoEngineering? This is the reasons for such extreme weather patterns. What is your opinion? Thanks!

I'm not sure that all El Nino

I'm not sure that all El Nino events are similar both in strength ( http://www.pmel.noaa.gov/tao/e... ) and their predominate weather effects( http://www.cpc.ncep.noaa.gov/p... ). As the CPC gif shows in the hyperlink above, for autumn in Southern Oregon/Northern California, one landscape can be dry whereas an adjacent landscape can be wet. Of course, these gifs are derived from historical data and thus are a statistical description.

Not all El Ninos are the

Not all El Ninos are the same. The Japanese have pointed out a Central Pacific El Nino style of event that leaves California dry. (They call it a El Nino Modoki.) Most standard El Ninos, ones that stretch accross the Central and East Pacific, even weak ones, bring some great rains. Even the Japanese at this point see a chance of a normal El Nino.

Agreed. The Modoki version is

Agreed. The Modoki version is similar but different but more data is needed to truly discern Modoki as something different. But to the point I was trying to make, for the State of Jefferson in northernmost California (CA), an autumnal El Nino would lead to anomalously low precipitation for those months. Thus I'd be careful for what I wished for.
Too El Nino in California is not the same as El Nino in Nebraska (NE). In both cases, these states are trying to grow food with a finite supply of water but in the face of growing demand for the water from other users. In my estimation, when groundwater supplies are exhausted in CA and NE, irrigation for food will cease, and what now would seem to be a "Black Swan event" will have transpired. If only we knew now what we'll know then. Oh wait. We do. It's just a lack of will, more than money, to prepare for such an outcome. Climate change such as the Arctic Amplification and changes in polar jet stream meanders are a tocsin or early warning of catastrophic change from today's climate to a different climate regime; e.g., wet is getting wetter and dry is getting drier. I've read the Farmers Almanac since I was quite young. I think that prognostication would probably have been quite good from 1950 through 1979 since climate was rather static or stationary back then. But given the recent changes in the various states of the ocean, atmosphere, and land, I would be surprised if anyone could accurately predict future weather based on prior climate. So kudos to you for trying.

Come on El Nino!

Come on El Nino!

PDO may not be entirely

PDO may not be entirely causative. Recent Arctic warming has led to changes in the position and strength of the polar jet stream or what has been termed the "Arctic Amplification" (AA). Due to AA, we see a slowing down of and large meanders in the polar jet. Indeed the effects of the AA may be more explanatory of the weather in the US this year.

Good point! There is no

Good point! There is no single cause of drought. The PDO is a major player in California weather, but not the only one. Historically, when the PDO is negative, the West is more sensitive to a variety of factors and more easily turns dry.

The change in phase or sign

The change in phase or sign of PDO certainly influences climate over longer time scales (annual to decadal). And indeed our physical infrastructure and regulatory systems seem to be designed for that type of climate regime. But, it seems that the switch from drought to atmospheric river then back that appears to be occurring over short time periods (say on the order of weeks to months) may be a new climate regime that seems that modern societies have not evolved with; such rapid changes in climate probably and apparently was not typical over the Holocene. If anything these rapid changes in weather shows us that our present-day resilience to these perturbations in weather is quite non-resilient. Hot dry dusty drought punctuated by high intensity but short lived storms followed by drought is something that our society did not arise from. Likewise, rapid and large changes in the polar jet stream have lead to conditions that some modern-day communities in the US and elsewhere seem ill equipped to handle (e.g., Jan 2014 Atlanta GA).

Hi, Sandy,  Thank you for

Hi, Sandy,  Thank you for taking the time to write and express your disappointment with the 2014 Almanac weather forecast. It's hard to read/hear, but we understand and appreciate that you cared enough to tell us.
I can not imagine how hard it must be for you to read the Almanac forecast and not see it "come to life." We appreciate your faith in our predictions and we are sorry that we have not fulfilled your expectations—and ours, which were for rain.
As you may know, the Almanac forecasts are made the previous year; the winter forecast was researched and delivered in winter 2013. Evelyn Browning Garriss writes this blog weekly, and so she is describing current events with the benefit of being in the moment.
Our meteorologist is not the only professional prognosticator who did not anticipate this wild swing by the jet stream and so the ensuing results explained above. Although it may be small comfort, the season, the year, is not over. As a saying goes, it only takes a day to change. 
Thank you for your belief in what we do (even though I know that faith is diminished...). Loyalty like yours means the world to us.
The Almanac Editors

Why with this "PDO"

Why with this "PDO" information did "The Old Farmer's Almanac" predict wetter than normal January and February 2014 for the California Pacific north west. You had my hopes up because I believed you. Now I have little to no hope at all for us. It's going to be another drought probably worse than the mid 70's. We haven't seen a drop of rain in months. Our lakes are mud puddles; I'm scared to death over this. I feel like we may never see rain again. That's how bleak our outlook is. Now why again did you mis-lead us with the phony prediction of "Wetter than normal Jan. and Feb. 2014"? Just to get our hopes up just to be dashed?
I'm sorry, I'm so scared that I'm lashing out at anybody to blame this frightening situation on. I once believed in you, not now, you'll have to prove yourself again to me in a big way to make me a believer again. Sadly, yours truly, Sandy Wilkins

For Sandy and all, We have no

For Sandy and all,
We have no one to blame for this, but ourselves.
We have been told for years that we must reduce our "carbon footprint" and cut back on our use of petroleum products. Few have listened. Now Mother Nature is making the changes for us, whether we like it or not.
I am an avid gardener and live in California as well. Believe me, I am not pleased with this situation either. In the years ahead, we will have to learn to conserve, reuse and live sustainably or we will all have a very hard time.


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