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November-December 2015

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What You Need to Know to Understand the Current El Niño

By August 2015, people across the West were beginning to dream that a potentially strong El Niño, which NOAA was forecasting for late 2015–early 2016, could bring relief from devastating drought in California and elsewhere in the West.

Clearly, during the summer of 2015, many were pinning their hopes on the fact that the strong El Niño that forecasters were saying should affect global weather during late 2015 and early 2016 could bring drought relief to the western United States. In contrast, when discussing past El Niños, such as the strong one of 1997–1998, the major focus before the El Niño began, while it was occurring, and afterward was not on drought relief but on floods and other related costly and deadly weather events.

This difference in focus raises the question: Is El Niño a misunderstood phenomenon?

Looking Forward to El Niño

On July 23, 2015, the Los Angeles Times published stories about four inches of hail falling on Interstate 80 around Donner Summit between Sacramento, California, and Reno, Nevada, and another story about heavy rain causing a rockslide that closed a Yosemite National Park entrance road. Headlines on both stories credited El Niño for the precipitation. The story about the hail said it “was just the latest strange weather to hit the Sierra Nevada, influenced by the weather-changing phenomenon El Niño.” For months, climate scientists had been saying that El Niño is more likely than not to bring more rain to Southern California this winter.

Even better for those looking for drought relief, some forecasters were saying the coming 2015–2016 El Niño could be similar to the big 1982–1983 and 1997–1998 events, which helped bring record amounts of rain and snow to large parts of California and other parts of the West. The distribution of California rainfall during the 1997–1998 winter was particularly fortuitous, because even though the state saw nearly twice its normal rainfall, that rainfall was spread over twice the normal number of rainy days, which mitigated large-scale flooding.

Nevertheless, crediting the El Niño, which had begun forming earlier in the year, for July rain and hail is an example of “wish-casting.” With these meteorological events, and any others that might occur during an El Niño event, you should be cautious about directly attributing them to El Niño. California has had July rain and hailstorms in other years. And looking at past El Niño years, there is no clear summer pattern attributable to El Niño.

A better summer sign that an El Niño was already affecting the weather and was very likely to continue affecting it was the NOAA Climate Prediction Center's August 6 update of the outlook for the rest of the June 1–November 30, 2015, hurricane season. It predicted a total of six to 10 named storms (including the three that had already occurred), compared to the long-term average of 12 each season. NOAA also gave 90% odds for fewer hurricanes than the seasonal average. These are the highest odds NOAA had given for a below-normal season since it started issuing hurricane season outlooks in 1998.

In the outlook, NOAA said: “Conditions associated with “a significant El Niño, such as strong vertical wind shear and enhanced sinking motion across the tropical Atlantic and Caribbean Sea, are now present. These conditions make it difficult for storms to develop, and they are predicted to continue through the remaining four months of the hurricane season.” NOAA also said the El Niño is forecast to continue at least through the end of the hurricane season on November 30.

Then, on August 13, the Climate Analysis Center issued an El Niño advisory, saying that there is a greater than 90% chance that El Ninño will continue through the Northern Hemisphere winter 2015–2016, and around an 85% chance it will last into early spring 2016: “All models surveyed predict El Ninño to continue into the Northern Hemisphere spring 2016, and all multi-model averages predict a strong event at its peak in late fall, early winter.” The advisory noted that while the El Niño was already putting a damper on hurricanes, any effects across North America weren't likely to show up before late fall.

What this will ultimately mean as far as the 2015–2016 winter is really a multi-step process. First, there needs to be strong confidence, as evidenced by the 90% probability from NOAA, that El Niño will still be in play come the winter months. Next, the ultimate meteorological outcomes are strongly dependent on the strength of the El Niño, with stronger events increasing both the likelihood and impacts in a given year.

However, El Niño is only one player in any year's climate, albeit the strongest, with other players such as the Arctic Oscillation, North Atlantic Oscillation, and Pacific Decadal Oscillation influencing what finally occurs. Consequently, no two El Niños, even if they have the same strength, are alike.

Across the United States during strong and very strong El Niños, there is some commonality in wintertime patterns. The most noticeable “signal” is in the above normal precipitation that spreads from California (especially the southern half) and across the southern tier of states, while the Pacific Northwest typically sees much lower than normal precipitation. The same meteorological pattern also translates into cooler average temperatures across the southern United States, while the northern tier of states from the Pacific to the Great Lakes is often warmer than average.

The impacts of El Niño are not just seen in the United States. In addition to impacting the western hemisphere hurricanes season, they are also manifested in drought conditions for Southeast Asia, Indonesia, and northern Australia.

What in the World Is an El Niño?

The first thing to understand is that an El Niño is not some kind of huge storm, or a precipitation anomaly such as a drought or flooding rain. In fact, “El Niño” refers to one phase of widespread changes in patterns of sea-surface temperatures, sea levels, trade winds, and locations of the world's largest thunderstorms. These tropical Pacific changes, in turn, affect global scale jet stream winds and thus weather patterns in far-away places.

Peruvian fisherman were the first to use the term “El Niño” to refer to a warming of the ocean off South America's West Coast every few years around Christmas time. It means “little boy,” but when capitalized it originally meant “the Christ Child.” The ocean warming cuts off cold, upwelling water that brings up nutrients, which feed a rich food web including huge amounts of small fish such as anchovies. These fish are important—the U.N. Food and Agriculture organization reports that the food web yields more fish than any other wild species in the world. While you might think of anchovies as something you do or don't put on pizza, they are an important source of food, mainly fishmeal that's fed to farmed fish and other animals.

What happens along South America's Pacific Coast is only part of what we mean today when we talk about El Niño. In fact, today the term “El Niño” is globally known as the name of a widespread weather and climate phenomenon centered in the tropical Pacific Ocean.

In the 1920s, Sir Gilbert Walker, a British meteorologist who was working in India on ways to predict the Indian monsoon, dug into Pacific and Indian Ocean region weather data. He discovered that when atmospheric pressures at Tahiti and Easter Island in the middle of the tropical Pacific were low, pressures in Darwin on Australia's northern coast were high and vice versa. He named this pressure seesaw “the Southern Oscillation,” but neither he nor other meteorologists saw any link to Peru's El Niño, which at the time wasn't widely known to the rest of the world.

The huge amounts of data collected during the 1957–1959 International Geophysical Year (IGY), which included the most extensive, simultaneous, global collection of meteorological, oceanographic, and other geophysical data ever made, enabled a few scientists to begin assembling our current picture of El Niño and related atmospheric-oceanic phenomena.

The ocean and lower atmosphere during the La Niña and neutral phases.

1982–1983 El Niño Caught Meteorologists by Surprise

Even though scientists had a fairly good understanding of El Niño by 1982, most forecasters or researchers didn't recognize the event that began that year as an El Niño until after it was almost over. Effects in the United States included winter storms that battered Southern California and floods across the southern United States. In contrast, states across the entire northern tier from Washington to New England were warmer and drier than average. Ski resorts had a terrible season.

La Niña and neutral phases have similar patterns of ocean temperatures, but the cool water is colder during a La Niña, which helps amplify La Niña's effects.

Some of the El Niño's most striking effects were in the central Pacific, where an unprecedented five hurricanes hit French Polynesia, and Hurricane Iwa, the strongest on record up to then, hit Hawaii. In contrast only six tropical storms formed in the Atlantic Basin, and only two became hurricanes with neither hitting land. While storms with wind, rain, and snow were hitting Southern California and places along South America's Pacific Coast, on the other side of the Pacific, Australia and Indonesia were suffering from drought and forest fires.

The ocean and lower atmosphere during an El Niño.

Although a few meteorologists and oceanographers had an inkling of warming in the tropical Pacific in general, the big 1982–1983 event caught most of the scientific community off guard because ash from the huge April 4, 1982, eruption of the El Chichon volcano in Mexico had spread across the tropical Pacific, attenuating ocean temperature data from the NOAA-7 satellite, which had been launched four months earlier.

All El Niños are characterized by warmer than average water in the central and eastern tropics of the Pacific Ocean, but they differ in the details.

In fact, during the December 1982 fall meeting of the American Geophysical Union in San Francisco, California, scientists seriously discussed the hypothesis that the El Chichon eruption had triggered the El Niño. This idea didn't last long; on April 5, 1983, The New York Times quoted Eugene Rasmusson of the NOAA's Climate Analysis Center as saying the volcano had nothing to do with the El Niño. Instead, he said, “little heed was paid at the time” to important data, including the beginning of a Southern Oscillation shift to the El Niño phase before the volcano erupted.

Missing the start of the 1993 El Niño helped prompt the United States and Japan to install approximately 70 buoys moored across the tropical Pacific that report not only sea-surface temperatures and other weather observations, but also underwater temperatures and currents, which give more detail about what El Niño and related phenomena are doing. Data from these buoys have helped to allow better quantifying of El Niño events with the Oceanic Niño Index (ONI). The ONI is based on the sea surface temperature anomaly (SSTA) in a rectangular region of the tropical Pacific, identified as region 3.4, that is between 5° north and 5° south latitude and from 120° west to 170° west longitude. When the average SSTA in the Niño 3.4 region exceeds +0.5°C, it is at the threshold for a weak El Niño. When it reaches +1.0°C, it is categorized as a moderate El Niño, and above +1.5°C as a strong El Niño. An important caveat with using SSTA in categorizing El Niño is that the warming of the tropical waters must “couple” with changes in the atmosphere. One of these is the reversal of the tropical trade winds. When this does not happen, a true El Niño may not emerge, as happened during the winter of 2014–2015.

It's More Than El Niño

Since the 1980s, researchers have learned much more about El Niño, including the fact that it's a phase of the El Niño Southern Oscillation (ENSO), which has an El Niño, a neutral, and a La Niña phase.

In 1997, in contrast to the 1982–1983 event, the El Niño was forecast well in advance and people, especially in California, responded ahead of time. These forecasts led governments and individuals to prepare for storms like those the 1982–1983 El Niño brought. In California and other parts of the West, NWS offices spent much of the fall briefing other local, state, and federal agencies that a strong El Niño was imminent, and that the prospects of a wet winter were becoming greater as El Niño continued to strengthen. Also in contrast to the “stealth” 1982–1983 El Niño, by the fall of 1997, late-night television talk show hosts, and others such as the late-great Chris Farley on Saturday Night Live, were making jokes about El Niño.

El Niño Brings Good News, as Well as Bad

Over the years, news stories and other reports have focused on the harmful aspects of El Niño, but it's not all bad news. In fact, many of the stories during the summer of 2015 focused on the possibility of the new El Niño easing western drought, and probably reducing the numbers of Atlantic Ocean, Caribbean Sea, and Gulf of Mexico hurricanes.

Some of the 1982–1983 El Niño's most striking effects were in the central Pacific, where an unprecedented five hurricanes hit French Polynesia. Hurricane Iwa, the strongest on record up to then, hit Hawaii.

During and after the 1997–1998 El Niño, the focus was on the storms and flooding rain, especially in Southern California and across the United States to the Atlantic Coast. NOAA's Climate Analysis Center summed up the effects: “Overall, the winter (December 1997–February 1998) was the second warmest and seventh wettest since 1895. Severe weather events included flooding in the southeast, an ice storm in the northeast, flooding in California, and tornadoes in Florida.”

Nevertheless, the 1997–1998 El Niño possibly saved a few hundred lives and helped the United States economy, climatologist Stanley A. Changnon concluded in a study he conducted and described in the September 1999 issue of the Bulletin of the American Meteorological Society. For example, while El Niño–related weather was blamed for 189 deaths, Changnon found that as few as 100 people died in winter cold and storms during the 1997–1998 El Niño, which is well below the average of 850 in the few years before. Generally mild temperatures “greatly reduced lives lost to extreme cold,” Changnon wrote, and there also were fewer weather-related auto accidents and deaths in winter storms. All in all, Changnon said, “If you treat it as an economic outcome for the country, most of the country benefited.”

What the winter of 2015–2016 will bring in terms of rainfall for the West, potential flooding, and warmer temperatures remains to be seen. And many caution that even if California does receive above average precipitation this winter, the additional rain is unlikely to end the drought, given how great the rainfall deficit currently is. Still, as Californians say, every bit helps, and if the costs and benefits of the 2015–2016 El Niño turn out to balance in ways similar to the 1997–1998 event, we can safely welcome this fascinating weather phenomena to our shores this winter.

JACK WILLIAMS was the founding weather editor of USA TODAY and is now a freelance writer. He's the author or co-author of seven books, five of which are about weather.

JAN NULL, Certified Consulting Meteorologist, is founder of Golden Gate Weather Services, a part-time faculty member at San Jose State University, and a former Lead Forecaster with the National Weather Service.       

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