La Nina Diminishes

May 23, 2008

By Elwynn Taylor, Department of Agronomy

The La Nina of the past several months as determined by the 90-day average Southern Oscillation Index (SOI) has ended. The SOI is a measure of the atmospheric pressure deviation from normal and directly influences meteorological conditions in numerous distant locations. The SOI diminished to 0.8 standard deviations on May 19, 2008. 

Although now in “neutral” condition, there is normally a time lag and risk associated with the La Nina though clearly reduced does not fully disappear at least for several weeks (often about 6 weeks). A significant number of (but by no means all) severe droughts in the Midwest are associated with La Nina. 

Planting under less-than-favorable conditions tends to exacerbate the impact of subsequent hot and dry weather. Drought in the southeastern U.S. is often a precursor to development of drought in the Corn Belt. The adverse factors do not make widespread drought likely for 2008 but below trend crop yields are and remain likely.

I will make my next computation of “most likely yield” during early June. At this time it appears that the previously estimated most likely yield of 142 bushels per acre for U.S. corn will be increase somewhat. 

Elwynn Taylor is a professor with responsibilities for developing and implementing extension education and information programs in agricultural climatology.

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Elwynn Taylor Professor of Ag Meteorology

Dr. S. Elwynn Taylor is the extension climatologist at Iowa State University, and is well known for his analysis of weather influence on the Midwest. He is widely recognized for his clear explanations of the complexities of long-term weather variability. Before moving to Iowa in 1979, he was a me...