Ag Weather Forum

NOAA Pacific Ocean Analytics Support Ideas of La Nina Holding Off Until Later in Summer

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
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Major Pacific Ocean measurements still indicate La Nina has not elbowed its way onto the long-range ocean temperature and barometric pressure scene just yet. (DTN photo by Bryce Anderson)

As the 2024 United States corn crop moves toward the all-important pollination time frame, a key Pacific Ocean temperature reading, the Oceanic Nino Index (ONI), goes along with other perspectives in the weather community which have emphasized the prospects of La Nina development holding off until later this summer, after most pollination has occurred.

The ONI is defined in a 2009 blog post by climate science writer Rebecca Lindsey this way: "The Oceanic Nino Index (ONI) is NOAA's primary index for tracking the ocean part of ENSO, the El Nino-Southern Oscillation climate pattern. The ONI is the rolling three-month average temperature anomaly -- difference from average -- in the surface waters of the east-central tropical Pacific, near the International Dateline. Index values of +0.5 or higher indicate El Nino. Values of -0.5 or lower indicate La Nina."

The rolling three-month average may lag some other benchmarks pointing to either El Nino or La Nina; however, the rolling average also avoids the shorter-term back and forth of temperature and pressure interaction. Values are presented in degrees Celsius.

The most recent ONI calculation is for the March-April-May (MAM) period, and that rolling average came in at +0.7, which is still in the El Nino category. A review of this value compared with the most recent top analog years compiled by DTN's long-range forecast team shows that the 2024 MAM Oceanic Nino Index came in warmer than all but two of the top six years in DTN's analog year array. Those years are: 2020, 2005, 2010, 2016, 1998 and 2001.

The March-April-May 3-month Oceanic Nino Index rolling average in the top six DTN analog years looks like this: 2020 +0.2; 2005 +0.4; 2010 +0.4; 2016 +0.9; 1998 +1.0; and 2001 -0.3. The 2024 ONI reading for the MAM period of +0.7 is only surpassed by 2016 and 1998.

Continuing through the growing seasons, the top DTN analog years showed the ONI moving into La Nina at -0.6 during July-August-September 2020; Neutral through the rest of the growing season in 2005; a La Nina value of -0.7 during May-June-July in 2010; a La Nina value of -0.5 during July-August-September in 2016; a La Nina value of -0.8 during June-July-August in 1998; and Neutral through the rest of the growing season in 2001.

Looking at the DTN analog years through this NOAA Oceanic Nino Index lens gives a strong indication that 2010, with its La Nina development in late spring-early summer, will not be matched in the ONI rolling average evolution. This offers a boost to ideas that corn will be able to go through pollination without a La Nina-fueled spell of constant heat and dryness.

Additional comments on later-summer La Nina development crop impact are available here: "La Nina Taking Longer to Develop, A Good Thing for US Agriculture?" at….

Bryce Anderson can be reached at


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