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El Niño Pattern Building; Cooler Midwest Summer Ahead?

After a couple years of floundering around in a seeming purgatory between La Niña and El Niño, the outlook has finally tilted toward the latter, a report that could foreshadow a break in crop-stressing weather conditions where it's needed most and more favorable crop weather for the Corn Belt.

Right now, El Niño Southern Oscillation (ENSO) is "becoming more prevalent" in the equatorial Pacific Ocean, a sign that the pattern is shifting toward the one that's typified by cooler, damper summer weather conditions in the Midwest and better growing conditions in the western U.S., where a devastating drought is entering its fourth year. When temperatures in this region of the Pacific rise, it's a sign that El Niño is more likely, and according to MDA Weather Services senior ag meteorologist Don Keeney, temperatures have warmed by 0.2 degrees Celsius, taking ENSO into the "moderate El Niño" range. As of now, there's reason to believe the trend will continue in that direction.

"Sea surface temperature (SST) anomalies may increase further in the coming weeks given the very warm subsurface temperature anomalies seen in the central and eastern equatorial Pacific," Keeney says. "The continued increase in equatorial Pacific SSTs increases confidence in El Niño persisting through summer and having a greater influence on atmospheric circulations during the season."

Translation: Better crop weather may be the theme for the corn and soybean growing season in the Midwest this year.

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"Last winter's weather forecaster consensus of a back-loaded colder-than-normal winter that was warmer than the prior winter worked out very well, while last summer's bearish consensus also largely succeeded," says Commodity Weather Group (CWG) meteorologist Matt Rogers. "Right now, it seems like the summer consensus is for a cool-leaning summer with lower demand vs. 2014 as we hold in an El Niño background state." 

Like anything concerning the weather, El Niño's typical performance is hardly a sure thing. Just in the last three decades, two anomalous years dominated by the weather pattern make it difficult to predict how the summer growing season will unfold, both with sharply different weather conditions. Rogers says 1987 was the first "consensus-buster" year that, though beginning with an El Niño pattern, ultimately unfolded into a hotter-than-normal summer for the Midwest.

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"1987 is probably the biggest heat risk I can imagine basically because it was the only El Niño summer with a solid positive Pacific Decadal Oscillation (+PDO) that was hot from the Midwest to the Mid-Atlantic. How could we get there? A positive PDO is put together in two parts: Cool water in the North Central Pacific and a warm water 'horseshoe' around it on the eastern side. 1987 was +PDO more due to its cool pool in the middle than the warmth along the North American shores."

On the other side of the spectrum, El Niño could strengthen in its effects to the Midwest, like in 2004. That year, warming in the Pacific caused the jet stream to shift more than normal, causing a broader-scale cooldown for much of the nation's center.

"While the consensus may win with a cooler-leaning summer that is cooler than last year, could everyone underestimate the degree of cooling? Is a more intensely cool 2009, 2004, 2000, or 1997 summer on the way? My main concern is the super-strong positive Pacific Decadal Oscillation (PDO), particularly the warmer eastern Pacific waters part with well above-normal water temperatures from the Gulf of Alaska to the California Baja in Mexico," Rogers adds. "As the jet stream lifts north seasonally, these warm waters could have a stronger influence, offering a feedback to strengthen warm West Coast ridges with counteracting very strong Eastern cool troughs."

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Editor's Note: Maps courtesy CWG.

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