How Long Will La Nina Last In 2011?

How Long Will La Nina Last In 2011?

Keep an eye on what happens with the La Nina weather pattern. "If it persists through June, that would put the U.S. at risk of below trendline yields in 2011, and likely 4 or 5 bushels below what we had in 2010 for a U.S. corn yield average," says ISU climatologist Elwynn Taylor.

Climatologists are watching the current La Nina weather system for clues as to what kind of growing season the U.S. Corn Belt will have in 2011. If the La Nina begins to fade away this spring and is completely gone by the first of June, that scenario would indicate favorable summer weather. But if La Nina hangs around through June, a significant drought is more likely.

A La Nina occurs when surface water temperatures in the central and eastern Pacific Ocean near the equator become cooler than normal. The cooler water in this region shifts the strength and position of the major air flow pattern. This includes the pattern responsible for movement of weather systems from the Pacific eastward through the continental United States and affects storm activity in the Gulf of Mexico.

The U.S. Climate Prediction Center in March released a report saying La Nina should be gone by June. The report says the majority of weather computer models are now predicting a return to neutral conditions in the northern hemisphere this summer.

Which computer models does Elwynn Taylor believe are correct?

The current La Nina event began last August and September. "It would be wonderful if this La Nina is gone by June," says Elwynn Taylor, Iowa State University Extension climatologist. "That would really reduce the risk of having a bad year for crops in the U.S. Corn Belt. But having a majority isn't the way science works. The majority doesn't rule when it comes to predicting weather. It's the forecast that is right that rules."

Considering the La Nina computer models that are currently predicting that La Nina will fade away by June, and instead of going with the forecast that the majority of the models agree upon, "I like to go with the track record," says Taylor. And which of the models tends to be the most accurate? Taylor says one from Colorado has the best record, and it is not in the majority regarding the current La Nina. In fact, the Colorado model is now predicting the odds are substantially above 50% that the La Nina will remain into summer, if not through summer. That's not good news for the U.S. Corn Belt.

"This current La Nina is a strong one," says Taylor. "It's No. 3 in historical strength. It's a bit weaker than the one we had in 1974 and a bit stronger than the one in 1955. Both of those were bad years for crops in Iowa and the Midwest."

If La Nina continues into June, expect below average corn yields

So, presently, La Nina is holding strong. Given the current conditions of entering spring with a strong La Nina, what is Taylor's best guess on the average yield for U.S. corn in 2011? "The trend is right at 160 bushels per acre for a U.S. average," he says. "That's what we'd expect with favorable weather in the U.S. Corn Belt in 2011. However, if La Nina is still here in June, the yield will likely be around 148 bushels per acre."

That would be about 4 or 5 bushels less than what the U.S. corn yield averaged in 2010, and a whopping 12 bushels below the long-time trend.

What if La Nina ends during the month of June and not before June 1? The odds would favor reduced yields, yields would be hurt. "If La Nina ends before June, that's when it makes the big difference," says Taylor. How long before June? "We need to have it gone by the first of June, according to the weather records we have from the past," he says.

If La Nina stays as strong as today, odds are 33% for drought

Taylor isn't necessarily predicting the U.S. Corn Belt will have a drought during the 2011 growing season. But with La Nina where it is today, the odds are about a 33% chance of a significant drought occurring this summer.

When will we know more? When could we see signs that would indicate the trend of La Nina may be ending before June? "We get an update on La Nina and the long range weather outlook usually during the first week of each month," says Taylor. "We're looking forward to the April outlook. Usually, by April 15 the summer weather pattern is making itself known."

Here's how to follow Elwynn's updates and weather observations

For Elwynn Taylor's latest weather updates and analysis on the Web, just Google "Where's Elwynn?" That will take you to his website. On Twitter, go to twitter.com\ElwynnTaylor.

Summing up: Whether or not the current La Nina event fades away, this spring will give clues for the 2011 U.S. growing season weather and yields. There remains considerable uncertainty as to whether La Nina will last into summer. However, if La Nina fades completely away by June 1 that would favor crop yields in the U.S. Corn Belt in 2011.

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