Ag Weather Forum

Greater Chance For La Nina

By Bryce Anderson , DTN Ag Meteorologist and DTN Analyst
Forecast model updates put La Nina formation at close to 50 percent chance during the last half of the summer--during fill stages for crops. (IRI graphic by Nick Scalise)

Mid-January forecast model updates done by the International Research Institute on Climate and Society (IRI) at Columbia University have both increased the odds for La Nina development in the Pacific Ocean AND moved the timeline for that to happen well into the late-summer time frame. That's the big highlight in the IRI report posted Thursday, January 21, 2015.

The mid-January forecast has El Nino (warm Pacific Ocean waters) continuing through late spring-early summer, with a near 70 percent chance for El Nino to still be around in the April/May/June period. Then, there's a big switch indicated--with a Neutral phase having the highest chance in May/June/July and June/July/August. Then, Pacific waters are indicated to cool enough to possibly reach La Nina levels in the July/August/September period. Odds for La Nina continue to climb in the August/September/October and September/October/November periods.

La Nina forming during, say, late July into August, could be significant for the fill stages of corn and soybeans. Central U.S. conditions tend to be drier and hotter when La Nina is in effect. Such a pattern is not helpful for crops. It would be a big contrast to the past two growing seasons of 2014 and 2015, when mild summer temperatures allowed crops to get the most out of the filling time frame.

This latest view on the forecast comes with a couple reminders.

First--the forecast view is strictly "black box". The IRI describes the mid-January presentation as "...purely objective, based on regression, using equally weighted model predictions...". In other words, there is no input from forecasters in this presentation. It's strictly what the models are showing--with equal weight given to each forecast model. IRI will have a full forecast update in early February, which will feature both model input along with forecaster discussion and weighting of the models.

Second--a Pacific switch from El Nino to La Nina during mid to late summer does not automatically mean lower production. In the 1998 crop year, Pacific conditions changed from a very strong El Nino in winter and spring to La Nina by midsummer--the June/July/August period. La Nina remained in effect the rest of the crop year. But when it was all done, production did very well. U.S. corn production in 1998 was six percent more than 1997 at 9.76 billion bushels, and soybean production set a record for the time at 2.76 billion bushels.


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