The Pacific Southern Oscillation Index (SOI), which is faithfully tracked by the BOM, had a 30-day average value of plus 15.16 on Dec. 23, 2020. But it is much less than the December SOI value back in 2010.
In fact, the SOI moved to strong La Nina levels almost immediately, with the following monthly values in the last half of the year 2010: July 20.08; August 18.22; September 25.52; October 18.20; November 16.42; and December 27.03.
2020 shows a much lower intensity of this ENSO metric. Monthly SOI values for the last half of 2020 are: July 4.02 (below the La Nina 8.0 threshold); August 9.39; September 9.96; October 4.18 (slipping back below the La Nina threshold); November 9.14; and the December 22 30-day value at 15.16.
If the forecast of Pacific sea surface temperatures reaching ENSO neutral levels by possibly late January verifies, the suggestion is that the SOI atmospheric feature will also start relaxing and the La Nina re-constituting of the jet stream patterns will have a short shelf life during early 2021. This feature is obviously a key item in projecting crop weather impact.
Bryce Anderson can be reached at firstname.lastname@example.org
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