La Nina conditions now pose a significant risk to U.S. corn production in 2008, says IowaStateUniversity meteorologist Elwynn Taylor.
Positive values of the SOI (Southern Oscillation Index) are associated with stronger Pacific trade winds and warmer sea temperatures to the north of Australia, popularly known as a La Nina episode. "The 90-day SOI threshold of 0.80 was met on Christmas day," he says. "Threshold means that 54% of the time significant La Nina conditions (defined as a 5-month average exceeding 0.8) will develop."
Several research groups see some indication that the La Nina may diminish quickly and not pose a risk to U.S .crops. Nevertheless, it is now at the level to be considered a risk.
When the La Nina is in place in June and July the risk of a below trend yield in the U.S. Corn Belt is 70%, says Taylor. This risk is increased by scant subsoil moisture, the 19-year drought cycle, and existence of drought in the area of South Carolina.
"At this time the combined risk is a 68% chance of a below trend U.S. corn yield," says Taylor.
The USDA trend for 2008 has not yet been released but will likely be near 151.6 bushels per acre. The chance of a near record high yield (greater than 165 BPA) is at 15%; chances of drought (below 135 BPA) is 35%.
Not all meteorologists are convinced that this La Nina will remain strong during the 2008 growing season, since actual rainfall in December for California and Arizona weren't normal. "We got some significant rains, bucking trends," says Jeff Doran, a senior meteorologist at Planalytics, a weather forecasting company in Wayne, Penn.
In fact, not every El Nino or La Nina episode produces the same weather pattern across North America. And one of the differences with this winter's cool episode is the jet stream flow in the eastern Pacific created by the cooler than normal waters off the west coast of North America. Another wildcard is the warm Atlantic to the east of the Caribbean.
Current conditions have Planalytics meteorologists forecasting wet weather in the Pacific Northwest, significant moisture improvement in the southwest, normal precipitation in the western Corn Belt and wet weather in the eastern Corn Belt. The southeast will see some improvement, but not nearly enough to relieve drought by spring.
Doran and Senior meteorologist Fred Gesser offered their forecast in late December after analyzing the La Nina weather patterns, other analogues and past La Nina events for clues to the upcoming growing season.
North American Forecast
According to Planalytics, the southwestern U.S. will see significant improvement in the moisture profile by spring compared to last year, says Gesser. Pacific Northwest, Ohio, and the Tennessee valley will be wetter than normal through winter. The southeast will see some improvement, but not enough to pull the area out of drought. The hard red wheat belt of the plains will see normal winter rainfall, but this is not that much for western areas of the plains.
Climatologists often look to history to find clues that may help predict upcoming weather patterns. A La Nina occurred in December 1950, which resulted in good precipitation across the southeast in early 1951, as well as plentiful rains in the plains.
An even better match, in terms of sea surface temperatures across the globe, may be comparing Dec.-Feb. 1955-56, with today. After a La Nina in Dec. 1955, January and February 1956 produced a wet Pacific Northwest, dry conditions in the south west, a slightly dry Corn Belt, and plentiful rains in the southeast.
Southern Hemisphere Troubles
According to Planalytics, Argentina will continue to see dryness problems in grain production areas through January 2008.
Dryness in Northern Brazil caused a six-week delay to the start of its growing season, due mainly to cooler than normal sea surface temperatures. This could result in the soybean crop being more prone to Asian rust and other pests and diseases. Argentina has developed some dryness despite recent rains. Grain production areas will continue to be a problem through January followed by some improvement. A problematic shortage of rainfall is likely to spread into Brazil's Rio Grande Do Sul growing areas.
The La Nina that occurred in 2007 caused the lack of rainfall in Australia's main wheat growing regions, extending the drought there into its second season. But that should be changing.
"We're already seeing signs of improved moisture in Australia," says Doran. "Our outlook for wheat in Australia is much improved rainfall for 2008 in the wheat production areas."