Note DetailLa Nina Diminishes
5/19/2008 6:07:00 PM

The La Nina of the past several months as
determined by the 90-day average SOI has ended. 
The SOI (Southern Oscillation Index) 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 United States is often a precursor to
development of drought in the Corn Belt.  The
adverse factors do not make wide spread 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 BPA for U.S. corn will be
increase somewhat.  –Elwynn

Iowa State University Extension