Ag Weather Forum

Comments referring to a "rapidly-developing El Nino" continue to show up in market discussions. I noticed another one just this morning (Monday May 19). Much of this comment is focused on the steady progress eastward of a very large and very warm pool of water in the sub-surface levels of the Pacific Ocean, making its way eastward from southeast Asia during the past few months. This deep-lying pool of warm water is the biggest such feature since 1997; and, at that time, the presence of such a large warm-water pool was followed by a very strong El Nino event. Forecast models are calling for El Nino to form, possibly by as early as July.

By now, you are probably very familiar with the projections for U.S. crop yields with El Nino's presence. Corn output in excess of 165 bushels an acre has been discussed--which, of course, would be a new record, beating the 164.7 of 2009.

However, one key feature of either El Nino or La Nina development is the trend in barometric pressure in the equatorial Pacific known as the Southern Oscillation Index (SOI)--the comparison between barometer readings in the island of Tahiti and Darwin, Australia. Iowa State University research has found that the SOI 90-day running average needs to be at -8.0 or lower for El Nino to be a factor in the Midwest weather pattern.

As of Sunday, May 18, the SOI was a long way from that -8.0 level on the 90-day reading. In fact, the overall trend was a bit La Nina-ish. The daily SOI value was +17.3; 30-day +2.4; and 90-day -3.0. That's a far distance from El Nino on the SOI scale. El Nino may yet show up, but the idea of a "rapidly-developing" event seems like a big overstatement at this time.

As far as the storm system--and rainfall--indicated for the southern Plains later this week, its origin is from the Pacific Northwest instead of being brought in by a sustained El Nino-related jet stream. The influence of the large blocking high over Canada is still a part of the circulation that we see in the U.S. weather pattern going into the last half of May.

Bryce

Twitter @BAndersonDTN

(ES/AG/CZ)

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