Ag Weather Forum

IRI Backs Off On La Nina

Bryce Anderson
By  Bryce Anderson , DTN Senior Ag Meteorologist
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Latest official Pacific Ocean forecasts by the IRI climate science institute shows a later beginning, weaker and shorter La Nina event for the Pacific than the agency forecast earlier this year. (IRI graphic by Nick Scalise)

The latest installment in the "El Nino-La Nina-will it-won't it" saga has been offered by the International Research Institute on Climate and Society (IRI) in its latest Pacific Ocean sea surface temperature forecast. It features a big change -- certainly from what we saw earlier this year.

The latest Pacific temperature forecast, produced in conjunction with the U.S. Climate Prediction Center (part of NOAA), calls for the Pacific equator-region temperature pattern to stay neutral not only through the balance of this month, not only through August, but all the way through September as well. Forecasts earlier this year had pegged the Pacific to have a better-than-even chance at cooling enough to reach La Nina levels by August-September. That timeline has been pushed back; in fact, the highest chance for La Nina to be in play is the November/December/January period, but with only a 60% chance of that happening.

The scenario gets more interesting further out into late winter-early spring 2017. The February-to-April period now has an almost equal chance of either La Nina or neutral conditions: La Nina 48%, neutral 46%. That's a big difference from a 62% chance for La Nina that was featured in the mid-June IRI/CPC forecast. It also puts a dent in the idea that the very-strong 2015/2016 El Nino will be followed by a very-strong La Nina. The likelihood of that kind of a robust La Nina has been compromised notably in this forecast.

Implications for crop impact are twofold: 1) La Nina is almost certainly not going to be part of the U.S. crop weather scene during the balance of this 2016 season; 2) A weaker La Nina is not as threatening for dryness in southern Brazil and Argentina during the 2016/17 growing season, which will start in the Southern Hemisphere in October; 3) La Nina-induced dryness in the major U.S. crop areas has, at this time, a lower probability of developing.

DTN Ag Weather's position on the evolution of the Pacific in 2016 has consistently been that La Nina development was unlikely during the majority of the 2016 growing season. It appears that such an event, if it forms, will be after this season, but will also be one of quite short duration, and possibly not affect U.S crop weather next year either.

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