Ag Weather Forum
Early April Finds Australia SOI Pointing to La Nina
A key component of determining whether El Nino or La Nina are happening in the Pacific Ocean is pointing in the direction of La Nina.
That component is the Southern Oscillation Index (SOI). The SOI is defined by NOAA's Climate Prediction Center (CPC) as "based on the differences in air pressure anomaly between Tahiti and Darwin, Australia."
Measurements of the SOI on file at the Queensland, Australia, government's Long Paddock website date back to the 1870s. SOI 30-day average values greater than +7.0 indicate La Nina. The SOI, along with sea surface temperature conditions, determines whether the equatorial Pacific Ocean is in La Nina, El Nino or neutral.
P[L1] D[0x0] M[300x250] OOP[F] ADUNIT[] T[]
A look in 2025 at the SOI early April 30-day values shows that this feature is pointing in the direction of La Nina. The 30-day SOI value on April 7 was +10.40, which is greater than the La Nina benchmark reading of +7.0. This reading suggests that the large-scale winds in the atmosphere are in a La Nina pattern.
Effects of La Nina on U.S. crop weather are quite well-known. The two most notable effects are drier conditions in the Southwest and the Southern Plains, and wetter conditions in the eastern Midwest and the Mid-South. Recent extreme events -- including dust storms in the Plains during March and heavy rain and deadly flooding in the northern Delta and Ohio Valley during the first few days of April -- offer examples of how La Nina may have factored into these events.
Still to be determined is how long this SOI move into the La Nina category will remain. Pacific Ocean forecasts generally call for a neutral state as we move through the spring and summer months. However, the La Nina circulation can at times take longer to revert to neutral than one might think. And that characteristic can still lead to weather patterns showing a La Nina-type influence even if the official judgement of the Pacific Ocean condition is "neutral". Large atmospheric patterns definitely follow their own schedules.
More details on DTN's April forecast are available here: https://www.dtnpf.com/…
Bryce Anderson can be reached at bryce.anderson@dtn.com
(c) Copyright 2025 DTN, LLC. All rights reserved.