Note DetailLa Nina Reaches Threshold
12/26/2007 10:09:00 AM

La Nina Reaches Threshold 071226
La Nina conditions are now posing a significant
risk to US corn production in 2008.  The 90-day SOI
threshold of 0.80 was met on Christmas day.
Threshold means that 54% of the time significant La
Nina conditions (defined as a 5-month average
exceeding 0.8) will develop.  The 90-day threshold
gives a 20 to 60-day advance indication.   Several
research groups see some indication that the 
La Nina may diminish quickly and not pose a risk to
US crops.  Never the less, 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 US Corn Belt is 70%.  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 US corn yield. 
The USDA trend for 2008 has not yet been released
but will likely be near 151.6 BPA.   The chance of
a near record high yield is at 15% (greater than
165 BPA) and of drought (below 135 BPA) is 35%. 
The risk levels are the composite of the identified
climate risks and are expected to be updated in
late January.      E. Taylor   26 December 2007

Iowa State University Extension