Ag Weather Forum

Waiting on La Nina

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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World Agricultural Outlook Board meteorologist Harlan Shannon said past data suggests we have only a 50% chance of La Nina developing by the end of 2016. (DTN photo by Emily Unglesbee)

ARLINGTON, Va. (DTN) -- Don't look to the oceans to restore commodity prices to their past glory this summer, if World Agricultural Outlook Board meteorologist Harlan Shannon's forecast proves true.

A strong El Nino, such as we are experiencing now, takes time to wind down, he told an audience gathered for the USDA Ag Outlook Forum in Arlington, Virginia, Friday. While it's true that La Nina summers can bring hot, dry weather to key parts of the Midwest and Great Plains, La Nina has only a 50% chance of developing by the end of 2016 based on past transitions, he said.

More likely, sea surface temperatures will still be cooling to neutral levels this summer, and La Nina may develop by the end of 2016, Shannon said. However -- even without La Nina's drying effect -- past years featuring weakening El Nino conditions heading into the summer did tend to produce slightly drier than average conditions in the Corn Belt, he added.


Data compiled from past summers where La Nina developed show strong below-average moisture trends in the Midwest and Southern Plains, with above-average moisture in the western U.S.

That scenario -- La Nina developing rapidly in time to affect summer crops after a moderate-to-strong El Nino year -- has only a 50% chance of happening, according to weather models, Shannon said. There is a 70% to 80% chance that it will develop by the end of the next crop season, however.

Because the science of predicting the waxing and waning of El Nino and La Nina is far from precise, meteorologists look to analog years to see how similar conditions played out in past seasons. In particular, Shannon and his colleagues have compiled data from the years 1998, 1983 and 1973, when a strong El Nino had peaked and was slowing down going into the spring season.

In those years, the spring season tended to bring above-average rainfall in the far West, Southeast and Northeast, and stable moisture in the Midwest. However, the Southern Plains and upper Midwest saw below-average rainfall. The springs of these years also tended to be cooler than average across the U.S., with the exception of the Pacific Northwest, Shannon noted.

"Given how well these analogs have done in forecasting what we've seen this winter, there is reason to think they do a pretty good job in providing insights about this spring," he said. "The one area I'm a little skeptical about is the West. We haven't seen as much precipitation there as we expected in California, so I think whether these analogs pan out in this region -- I think there's reason to be concerned they won't at this point."

In the summer of these years, pockets of dryness emerged in the Southern Plains, Southeast, Northeast and the Midwest, with wetter conditions in the West, Shannon pointed out. Warmer-than-average summers were also likely for the eastern half of the country, he added.

"I'm not saying this is an absolute forecast for the upcoming spring and summer, but it's something to keep in mind," Shannon said.

Don't pin any hopes on catastrophic weather in Brazil, added World Agricultural Outlook Board deputy chief meteorologist Mark Brusberg.

"While [El Nino or La Nina] does impact weather locally in Brazil, it doesn't appear to impact agricultural production in a significant way that you can rely on in other parts of the Southern Hemisphere, such as South Africa, Argentina and Australia," he said.


California's historic drought has been eased by moisture from El Nino conditions recently, but many experts had hoped for more, Shannon said.

"After four years of drought, unfortunately they haven't gotten as much rain from this El Nino that a lot of people were banking on," he said. "California is running out of time to get beneficial rain from El Nino."

"The snowpack was pretty good across the West relative to last year," he added. "El Nino fueled near- to above-normal snowpack, but that was also disappointing -- people were expecting a lot more snow with an El Nino of this magnitude."

Shannon is also worried that the plentiful recent moisture in Texas might not continue for too long. "We can see drought creeping back into Texas toward the end of this winter," he said of the Drought Monitor.

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