Most weather forecast models have reliable accuracy only one week into the future - but what if La Niña gives us insight as far ahead as 2019?

Commodity markets have been fixated on the development of La Niña, or the cooling phase of Pacific Ocean surface temperatures. The agriculture market is more focused toward La Niña impacts on U.S. summer weather for corn and soybeans, while the energy industry is already looking ahead to what the winter months may have in store.

The warm phase of the El Niño-Southern Oscillation, El Niño, has recently died out and the cool La Niña phase is expected to begin within weeks. But the consequences of the impending La Niña may stretch much further than most people realize, as history shows that when La Niña comes, it is often slow to leave.

Cooler-than-average Pacific Ocean surface temperatures, known as a "negative" ENSO phase, can last for well over two years at a time. And when these waters get cold enough to turn into a La Niña phase, the strength of the event can lend clues to its possible course.

It would take a long time to list the specific global weather impacts by region. But the simple knowledge that Pacific sea surface temperatures could be cooler than normal over the next couple of years is very significant since it could change the short-term climate as well as the atmosphere within commodity markets.

La Niña has longevity

Both El Niño and La Niña cycle on a semi-regular basis, approximately every two to seven years. But historically, La Niña has had much greater staying power than its warm counterpart.http://pdf.reuters.com/pdfnews/pdfnews.asp?i=43059c3bf0e37541&u=2016-06-24T111652Z_GFXEC6O0VC4CC_1_RTRGFXG_BASEIMAGE.png

The typical lifespan of a La Niña event is roughly one year, which is three months longer than that of El Niño. On the top end, the record longevity for El Niño is 17 consecutive months between September 1986 and January 1988.

La Niña has met or exceeded this figure four times since 1950. The longest standing La Niña event immediately followed the record 1997/98 El Niño season and persisted for 32 consecutive months between July 1998 and February 2001.

In the past 66 years, there are two instances of three consecutive La Niña seasons. A third case exists in which the last year of the group fell just short of an official La Niña. There is no such statistic for El Niño (click for larger chart).

Both of the “three-peat” La Niña cases immediately followed massive El Niño events. This general trend likely assisted forecasters this year in calling for the impending La Niña well before the models.

Given the past behavior of La Niña, it is not too early to speculate beyond the 2016/17 time frame. Of the 23 La Niña and borderline La Niña events since 1950, 14 of them remained in negative ENSO territory into the following season (click for larger chart).http://pdf.reuters.com/pdfnews/pdfnews.asp?i=43059c3bf0e37541&u=2016-06-24T025352Z_GFXEC6O15DS6J_1_RTRGFXG_BASEIMAGE.png

At the wider scale, consecutive ENSO-negative years occur twice as often as consecutive ENSO-positive years. What all of this says is that although not impossible, a return to El Niño conditions in 2017 is statistically unlikely, and that the next two years will most likely contain neutral ENSO to La Niña conditions.

The exact course will depend greatly on the trends in the atmosphere. Some of the key determining variables include trade wind and pressure tendencies over the Pacific Ocean in addition to the Pacific Decadal Oscillation, a climate variability in the Pacific.

Strength matters

http://pdf.reuters.com/pdfnews/pdfnews.asp?i=43059c3bf0e37541&u=2016-06-24T025252Z_GFXEC6O15C44L_1_RTRGFXG_BASEIMAGE.pngHistory indicates that the strength of La Niña has bearing on ENSO in the following year. This can also give us insight into possible scenarios for the 2017/18 season, which is beyond the current range of forecast models.

Three separate groups of years can be carved out in Chart 2: Group 1 (strong La Niña), group 2 (moderate La Niña), and group 3 (weak/borderline La Niña) (click for larger chart).

When these three groups are charted separately, it is clear that strong La Niña events almost never give way to the positive ENSO regime toward the end of that year. However, four of five weak or borderline La Niña events turned into El Niño or close to it. (click for larger chart below).

The moderate scenario is more split with a slight favoring of negative, but a strong event was less likely to follow. The moderate scenario is what international climate models are currently predicting for the 2016/17 season (click for larger chart).http://pdf.reuters.com/pdfnews/pdfnews.asp?i=43059c3bf0e37541&u=2016-06-24T024708Z_GFXEC6O152KG6_1_RTRGFXG_BASEIMAGE.png

This does lend some validity to a potential resurgence of El Niño in 2017/18, but the strength of the upcoming cool event is not yet settled. It is very common for the models to increase predicted strength over time.

But what is important to recognize is that the atmospheric environment surrounding us for the past two years is in fact changing. If we truly observe negative ENSO for the next couple of years, both the global weather and the tone of the markets may be a bit different from what we have been used to lately.

http://pdf.reuters.com/pdfnews/pdfnews.asp?i=43059c3bf0e37541&u=2016-06-24T025154Z_GFXEC6O15AI5S_1_RTRGFXG_BASEIMAGE.png