La Nina Impacts Winter Weather in Corn Belt
Rod Swoboda
"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 recordbreaking 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 warmerthan-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."