Introduction

Dan Satterfield Chief Meteorologist

So what is an El Nino? Is it the opposite of a La Nina? I know that you’re probably thinking that it’s some weird ocean current that occasionally causes weather havoc around the world. Some folks get it confused with climate change as well, but I can tell you right now that El Nino’s have been happening since we humans were living in caves. There is, however, evidence that the warming planet may make the rarer Modoki El Nino develop more frequently, but this is still rather uncertain.

El Nino 101

El Nino’s are not just a change in the ocean, but instead are a naturally occurring oscillation of both the ocean and the atmosphere. The atmosphere and ocean actually affect each other, so give me a few minutes, and I’ll tell you all about it, and why you should care. If you have ever taken a dip in the ocean off of California, you know how much colder that water is than what we see here on Delmarva, and this is a crucial fact in the development of an El Nino.

While the Pacific Ocean off the coast of North and South America is rather cold, it’s just the opposite on the western side of the Pacific. Not only that, but the depth of that warm water is quite deep in the western Pacific, while what little warm water we have in the eastern Pacific is very shallow. The reason for this is the way the surface winds blow across the entire Pacific basin.

These winds usually blow from east to west, and pile up the warm surface water in the western Pacific. Cold water from the deep rises up along the California coast to replace the water being pushed west, and this also happens all the way down to South America. The rising cold water is called up-welling, and not only is it cold, but it is full of nutrients, that make the great anchovy fishery off Peru possible.

An El Nino episode happens when these winds blowing the warm water to the west collapse and a surge of warm water from the Asian side of the Pacific surges east all the way to the coast of the America’s. The water warms rapidly off the coast of Peru, the upwelling stops, and anchovy fishery collapses! Furthermore, that’s just the beginning of ocean and atmospheric changes that can have a large affect on the weather from Iceland to Australia, and even India.

This is the short version, but below are a series of four videos about El Nino (Meteorologists call El Nino and La Nina the Southern Oscillation), and they are well worth watching. They were produced by Taichiro Sakagami while he was a PhD student at Duke University, and they are embedded below. They have simple to understand graphics, and if you watch them you will know more about El Niño than 99 percent of the planet! Not bad for 24 minutes, eh?

El Niño Introduction

Beginning of El Nino

Peru During El Nino

Recovery of El Nino

If you watched the videos above, you now have an understanding of how El Nino is an oscillation of the atmosphere and ocean together, which causes some rather dramatic changes in weather patterns in some areas of the world. Now, let’s look at El Nino Modoki. Modoki is Japanese for “same but different,” and this is indeed the case. El Nino Modoki events are a rarer subset of regular El Nino’s, and are marked by warming water in the Pacific, but not along the Equator. Instead, the warming is in the mid-Pacific and the warming is not as strong as in regular El Nino events. Many times in a strong Modoki, water actually cools below normal off the coast of Peru, which is the opposite of a normal El Nino event (and what you see in a La Nina event).

The warming water over the Pacific also warms the atmosphere and this shifts the jet stream, but in a different way. While regular El Nino events tend to bring rain to California, a Modoki event brings drier than normal weather. Notice in the image to the left how much of the central Pacific is showing warmer that normal temperatures, especially along the equator. This is more typical of a Modoki El Nino. There also other changes, and in general the effects are stronger. Areas that get colder during the winter with El Nino get colder still with a Modoki event, but the areas affected also change. Here on Delmarva some of our coldest and snowiest winters happened during years with a Modoki El Nino. A big word of caution though: just like El Nino, each Modoki El Nino is different. We are only talking averages here!

So, now we finally get to the point of asking what kind of El Nino will we see this winter, if any? It does look like an El Nino is brewing but it does not look to be a strong one as of now. There are also signs that a Modoki El Nino may be trying to form as well, and to be frank, at this stage it is too early to say for sure which type of El Nino will develop! The odds are about 65 percent that we will see an event of some kind this winter, although the current projections (based on models and current sea water temperatures) indicate it is not likely to be a strong one. Keep in mind though, that this is a long-range forecast, and remember- we are LOUSY at them!

Enlarge The El Nino Modoki index forecast from the Japan Meteorological Agency does show that a weak to moderate event is possible this winter. Japan Meteorological Agency

The Japan Meteorological Agency has a running El Nino Modoki index and forecast, and as of today it does indicate that a weak to moderate El Nino Modoki is possible. The image on the left is a compilation of several different model runs, with each line representing a different model run. As you can see there is a great deal of spread, with the red line being an average.

Let’s assume that we do have a Modoki El Nino this winter and ask what kind of weather will this produce. There have been a few studies that looked at this, and for California the news is very bad. The worst drought on record is under way there and there were hopes that an El Nino this winter would break the drought. If a Modoki El Nino develops instead, the rain will probably not fall. Look at the image below comparing rainfall across the U.S. in an El Nino year, versus a Modoki year.

Keep in mind that these are averages of several different El Nino events, but the signal is clear that Modoki El Nino’s bring dry weather to much of the Western U.S.

Modoki El Nino in the Mid-Atlantic/Northeast U.S.

If you look at the years when there were significant Modoki El Nino events, you see that they include some rather cold and snowy winters in our neck of the woods. Everyone would agree that the winter of 2010 was pretty snowy and that was indeed a Modoki year. Yes, you can have a snowy winter when there is no El Nino, and you can have a mild winter when there is. But when you look at the averages, you start to see a pattern.

Enlarge The red on the above chart indicates El Nino Modoki Events. Japan Meteorological Agency

The two images below compare temperatures during El Nino events, and during El Nino Modoki events. Notice how the extremes are stronger (darker blue means colder) during the Modoki type events. The first thing you may notice is that the Western U.S. is much warmer and drier in a Modoki event than in a regular El Nino.

The opposite is true over the Eastern U.S., with cooler and wetter conditions than normal and cooler and wetter than a regular El Nino.

Enlarge Japan Meteorological Agency

The public tends to ask different questions after a significant weather event than meteorologists do. I often get questions asking what caused the tornado outbreak, or the cold winter etc. The correct question to ask is what were the CAUSES, because Mother Nature almost never makes it easy to ascribe a big weather event to one cause. The winter to come may very well be influenced by El Nino, and it may even be a Modoki-type event (although the model runs show a very weak one as of now), but there are other ocean and atmosphere cycles that will also play a role and perhaps even a dominant one. This is why long-range forecasting is so difficult; we have to know which cycle will play a role and how dominant it will be months in advance to make a decent long range forecast.

Another Possibility

There are other methods to make a long-range winter forecast and one of the newest (and increasingly popular) has to do with October snowfall in Siberia! A paper published (pdf) by Dr. Judah Cohen in 2011 showed a fascinating correlation between snowfall in Siberia, and the severity of the following winter over the eastern U.S. It seems that a snowy autumn in this part of Russia can lead to a pressure pattern in the upper atmosphere that favors cold air and snow in eastern North America. This may sound strange, but it actually makes sense to meteorologists because the jet stream acts like an old waterbed- if you push down in one area, it rises up in another.

Cohen has shown a remarkable correlation between the early autumn snow in Siberia, and the Arctic oscillation in the Atlantic. This pressure pattern is watched closely each winter because when it goes into a negative phase, the weather gets cold and usually snow in the Eastern U.S and Western Europe. Time well tell if this predictor works over many seasons, but it does show great promise.

You are probably wondering how the snow is looking this year in Siberia and the answer is that it came fast and heavy, much like it did in 2010 when we were hit by “Snowmageddon!” The graph below is courtesy of my friend (and long time Buffalo Meteorologist) Don Paul (@4warnweather), and it shows how the Siberian snowfall is running (The Rutgers University Global Snow Lab keeps a running total) this year.

The NOAA Climate Prediction Center has issued its winter outlook for the coming winter (see maps below), and you can see that they are factoring in a weak regular type El Nino into it. If we see a Modoki El Nino, then this forecast will probably be badly wrong. If the El Nino does not develop (or is very weak) then the signal from the Siberian snow may be the dominant one!

Enlarge NOAA Climate Prediction Center

NOAA is basing this year’s outlook primarily on the possibility of a weak El Nino and also on patterns of ocean temperature anomalies. Comparing the patterns with past winters having similar patterns is another tool that can be helpful in making a long-range forecast. There are several other ocean/ atmosphere oscillations that can be used to make a long-range forecast, but hopefully you now understand why none of them are a magic bullet.

Other Information

WBOC Weather Blog

NOAA’s El Nino Portal

Japan Meteorological Agency

Rutger’s University Global Snow Lab

NOAA Climate Change Prediction Center

About the Author

WBOC Chief Meteorologist Dan Satterfield has worked as a forecast meteorologist for more than 34 years. He is a graduate of the University of Oklahoma with a degree in meteorology (atmospheric physics) and has a master’s degree in Earth Science. Dan is a native of Oklahoma, and has worked as an on-air meteorologist in Orlando, Florida, Oklahoma, and most recently in Huntsville, Alabama. Dan also writes a popular Earth Science blog, the Wild Wild Science Journal for the American Geophysical Union. He also developed the Wild Wild Weather page to explain the science of weather to students in grades 2-7. Follow Dan on Twitter and Facebook.

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