(AgWeb) - The El Niño effect in the Pacific Ocean that brought unusually large snowfalls to the Midwest this winter is officially over. Good news for those who don’t like to shovel snow. But the patterns may be shaping up for a La Niña system that could bring extremely hot weather to the Midwest’s major row crop growing areas this summer. 

The National Weather Service’s Climate Prediction Center issued an alert Thursday saying the Pacific Ocean surface temperatures decreased between 0.5 and 1.0 degrees Celsius during May, bringing the end of El Niño. However, it cautions that several computer models are now indicating that La Niña will develop between June and August this summer. 

Iowa State University climatologist Elwynn Taylor says this may be reason for concern to farmers. He also says it’s certainly not time to panic just yet.

Taylor, who uses a different method for predicting La Niña conditions, looks at the standard deviation from normal in atmospheric pressure readings. His models confirm the dissipation of El Niño, and he says “we shot right through the neutral territory” and the pressure is currently 0.54 from normal on his index. La Niña will be confirmed if it reaches 0.8. (El Niño is confirmed when it reaches -0.8 standard deviation from normal.)

“If we have a La Niña by the end of June, we have a 70% historical chance of below-trendline yields. If we have neutral conditions, then of course we’re usually three bushels above the trendline. The neutral conditions the National Weather Service thinks are the most likely, and the La Niña is a definitive risk.”

The summer of 1988 is popular in discussions about La Niña effects, says Taylor, but he cautions that was an entirely different year. That year the El Niño dissipated in the winter of 1987 and the La Niña impact was already well established heading into the growing season.  

A more likely scenario may be the summer of 1983, when the La Niña effects took hold later in the growing season, as they might be doing right now. The summer didn’t have extremely high temperatures like the ones seen in 1988, but it did create a drought in the growing season. “It shifted out of El Niño and into La Niña during May and June, so that is a worry to us when we see it doing that again," Taylor says.

“In the past when it has started in June it tends to have more impact on Midwest corn than it does if it shows up in July or if it didn’t get there at all. La Niña tends to turn the weather loose to be a little bit more extreme in either direction, meaning the high temperatures can get higher and the low temperatures can get lower. I think that’s where the risk comes from.” 

Taylor stops short of predicting a 1983 repeat, cautioning that the National Weather Service still predicts more or less a repeat of last year’s growing season. He says monitoring the system needs to be done on a week-by-week basis right now. 

“If we get the high temperature extremes, that’s where the risk comes from. It doesn’t affect our rain in Iowa, Illinois and Indiana as much as some other places. But it does let the temperature be more extreme.”

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