Grain and oilseed crops may be threatened next year by a weather pattern known as La Nina, according to a private forecaster.

La Nina conditions have developed rapidly across the equatorial Pacific Ocean during the past few weeks, said Drew Lerner, president of World Weather Inc. in Overland Park, Kansas. He said that may indicate more dry weather in parts of South America in the next three months and a wet, cold start to the U.S. planting season in March.

La Nina, which means "the little girl" in Spanish, is caused by lower-than-normal surface-water temperatures in the Pacific. It can trigger widespread changes in weather around the world, including a higher-than-normal number of hurricanes in the Atlantic Ocean, Lerner said.

"The impact of La Nina conditions has already been noted in many areas, with more frequent rain in eastern Australia, wet weather in Indonesia, Malaysia and the Philippines as well as a drier bias in southeastern parts of South America," Lerner said in a Dec. 24 interview. "Confidence is quite strong that a full blown La Nina event is evolving."

The current weather patterns are more similar to a mature La Nina instead of a developing event because the last episode faded in May, leaving behind residual atmospheric conditions, Lerner said. The pocket of unusually cool Pacific water has quickly expanded west and extends to a greater depth than usual, signaling a stronger impact on next year's weather, he said.

"The colder surface temperatures become relative to normal, the higher the potential for La Nina and the stronger the event might become," Lerner said. "Below-average precipitation will continue in eastern Argentina, Uruguay, far southern Brazil and a part of Paraguay, but not necessarily a full-blown drought and major crop losses."

Stronger La Nina

The latest forecasts from the U.S. National Oceanic and Atmospheric Administration are now predicting a stronger La Nina event next year compared with projections a month ago, Lerner said. Conditions indicate that this La Nina also will last for an extended period, increasing the crop risks in both South America and in the U.S., Lerner said.

Soybean prices rose to a five-week high on Dec. 24 and corn gained for a third straight session on speculation that persistent dry weather will damage yields in Brazil and Argentina, the two biggest exporters of both crops after the U.S.

The La Nina pattern may also result in wet, cold weather in the U.S., which could affect planting next year, Lerner said.

Flooding, Reduced Planting

The cold Pacific Ocean waters earlier this year led to the worst flooding in the U.S. Midwest since 1993, Lerner said. The last time La Nina weather events occurred so close together, in 2001, 4.8 percent less corn was planted in the U.S. because of cold, wet conditions during the planting season. Farmers also planted 1.6 percent less acreage with soybeans in 2001 than surveys indicated they would, partly because of wet conditions.

The U.S. Midwest and northern Mississippi Delta region should have a significantly wetter, colder March and April, as farmers begin preparing seedbeds and applying fertilizer, Lerner said.

"We are going to see delayed plantings early in the season," he said