La Nina Impacts Winter Weather in Corn Belt

ISU climatologist says La Nina weather pattern could affect both U.S. and Brazil –and have an impact on South American soybean crop.

Published on: Dec 17, 2007

"We're moving into La Nina weather conditions," says Iowa State University Extension climatologist Elwynn Taylor. "Some of the forecasters believe the La Nina will reach its peak in January or February. Under La Nina, the temperature seems to be out of control. Warmer than usual, maybe record-breaking warm and maybe record breaking cold happening within a week of each other. Sometimes it happens within a day or two of each other.

"We are in for one of those types of more extreme winters, with both the warmer- than-normal and the colder-than-normal weather going on," says Taylor. How much snow will we pile up this winter? "We don't know but the amount of moisture we expect over the winter - what you get if you melt the snow and ice—will likely be on the shy side of usual," he adds, "just as November was a little below normal in precipitation. This is typical of La Nina."

What will happen when we get into late winter? "That's anyone's guess," he says. "But we do expect to see our share of extremes. The situation this winter is when you are traveling you'll say--Why couldn't I have timed this a little differently? When weather events come along every week or two, some of the storms are going to hit just when you didn't want them."

Odds favor drought sometime soon

What about drought? Are the odds still stacking up for a major drought in the Midwest in the near future - based on the climate cycles?

"Based on climate alone and what it has done in the past, we are due for a major Midwest drought," says Taylor. "The most recent major one was 1988. And to be 19 years apart, according to the records of the last 800 years, based on how the trees have responded and tree ring data, there is about 23 years between droughts. So yes, we are due for a major drought in the Midwest, but we don't know exactly which year it will come. It could be this year or next year or 2011."

Droughts usually come when there's a La Nina. But now we have a La Nina hitting us in the winter - and that may not be as bad, he says.

The current La Nina is more likely to have a negative impact on crops in Argentina and southern Brazil than the U.S., according to Taylor's analysis.

Watching southeast U.S. for clues

"However, of the past 17 major droughts - and that's all of the major droughts in the past century - 16 of them started in South Carolina," notes Taylor. "This year, South Carolina already has a drought going on. So there are a couple of bad omens out there signaling that 2008 could be the first major drought since 1988 in the Corn Belt. And the odds might even be favoring that. But that doesn't guarantee it is going to happen."

The El Nino phenomenon relates to changes in sea surface temperatures off the coast in the tropical Pacific Ocean. Increasing or decreasing ocean surface temperatures affect atmospheric pressure, which in turn impacts wind currents high aloft, he explains.

There are three phases to the cycle: El Nino (warm phase), neutral and La Nina (cool phase). How far above or below normal and where the temperature shift occurs helps determine its longevity and intensity. The more intense the cycle, the bigger the impact on global weather patterns.

Keep an eye on 2008 weather forecast

The long-range forecast issued by the National Weather Service for the winter months in the U.S. indicates a typical, La Nina-dominated winter, says Taylor.

"La Nina winters tend to be moist in the Ohio River Valley, and dry in the Western Corn Belt. The Northern Corn Belt may average a bit colder than usual. Northern regions near Canada could be considerably colder than normal. The southern Corn Belt most of the way to the Gulf Coast will likely be warm."

Moisture in the Ohio River Valley could be beneficial. Parts of Indiana, Kentucky, Illinois, Ohio and Missouri were very dry in 2007. But during the past 90 to 120 days, moisture fell across most of the Corn Belt, notes Taylor. That would be a positive point for beginning the 2008-cropping season.

"There hasn't been a widespread drought in the U.S. during an El Nino," he points out. "However, it's not uncommon to have a serious drought as an El Nino ends. The El Nino that ushered in 2007 faded by mid-season."

To follow the National Weather Service's long-term forecast, visit: www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=2. To monitor soil moisture recharge, visit: www.cpc.ncep.noaa.gov/products/precip/realtime/GIS/USMEX/USMEX-precip.shtml.