The agency released a report June 9 announcing an official end to El Nino and predicating the change. “Overall, ENSO-neutral conditions are present and La Nina is favored to develop during the Northern Hemisphere summer 2016, with about a 75% chance of La Nina during the fall and winter 2016-17,” the agency said.
El Nino and La Nina are opposite sides of the El Nino Southern Oscillation (ENSO), which describes a pattern of conditions that include ocean temperature and movement of the trade winds, said Tom DiLiberto, contract scientist with NOAA.
An El Nino is characterized by warmer than usual temperatures off the coast of South America and warmer winter conditions for many parts of North America, said NOAA. The event tends to bring favorable crop growing conditions in the Americas, but can have the opposite effect on production in China, India, Southeast Asia and Australia.
La Nina periods, however,are marked by below-average surface temperatures in the eastern topical Pacific, said NOAA. There also is a system of low air pressure in Indonesia and western tropical Pacific with a high air pressure region in the eastern tropical Pacific.
“It kind of swings like a pendulum between the three [El Nino, neutral and La Nina],” explained Jim Angel, Illinois climatologist with the Illinois Water Survey.
Currently, there is an ongoing neutral state, said DiLiberto. The agency looks at a three month averages to determine if the pattern is developing, he said.
“We declared El Nino in March of 2015 and certain parts of the globe may be ready to see it disappear,” he told us. “But it was one of the strongest that we had seen on record.”
The strength of the El Nino though does not necessarily correspond to a stronger La Nina, said DiLiberto. “It’s too early to say how [long] it [La Nina] will last, there have been short La Ninas and ones that have lasted years," he added.
The influence that a La Nina phenomenon could have on crop growth likely depends on when it arrives, Angel told us. “The faster it gets here the more effect it has on the growing season, if it shows up in September it won’t be much of a factor, if it shows up in July or August there may be more influence,” he added.
There is not always a consistent pattern in the weather the system brings with it, he said. It sometimes is linked with drought conditions during the feed crop growing season, but not always.
“There is a tendency to be on the warm and dry side as we move into the La Nina based on more recent events,” he said. “The classic case was 2011, the La Nina was not too extraordinary, but it showed up in July and August, and we got hot and dry [weather], and that continued into the fall and that set us up into the drought in 2012," said Angel.
The statistical trend during a La Nina is to have average or below average crop production, said Corey Cherr, head of agriculture and weather research and forecasts, Lanworth at Thomson Reuters, in a previous interview. “If you head toward La Nina you raise the warning flag of, at best it’s going to be normal, and at worst it will be really bad, and we’ll probably be in-between,” he added.
One question this year will be temperatures in July, said Angel. “Right now we’re running 3.7 degrees above normal and even if temperatures moderate, we’ll still end up with a June that is warmer than average and that’s likely to continue through September.”
However, it can be harder to see the influence of a La Nina in the summer months in the US, said DiLiberto.
“We’re looking at influences for the winter season,” he said. “During the winter, it’s drier than average conditions and colder than average temperatures in the Northeast and wetter in the Ohio River Valley and Pacific Northwest.”
It is more of a challenge to know what will happen in some areas of the country, including across the central plains region in the middle of the country, he said.
Another potential outcome of the move to a La Nina is a potential delay in spring crop planting, said Angel. “If it’s a cold winter, it takes a little longer for the ground to warm up and dry out,” he added.