The odds of the Pacific Ocean equatorial temperatures cooling to La Nina levels continue to be inched higher. The latest forecast model grouping put together by the International Research Institute on Climate and Society (IRI) now has a 52% chance of the equatorial Pacific cooling to La Nina levels (at least one-half degree Celsius below normal) during the summer season -- the June/July/August time frame. This is a big departure from the agency's mid-April forecast presentation. At that time, the June/July/August period had only a 31% chance for La Nina temperatures to develop at that time. La Nina odds increase to over 60% in July/August/September, over 70% in August/September/October, and around 75% during the rest of calendar year 2016.
What happened to cause this change in the forecast? Basically, the ocean is cooling down quickly. "During early 2016 the positive tropical Pacific SST anomaly was quickly weakening, now indicating only a weak El Nino. The atmospheric variables continue to support the El Nino pattern, but at much reduced strength. This includes just mildly weakened trade winds and excess rainfall in the central tropical Pacific, failing to extend eastward as it did in previous months. Most ENSO (El Nino Southern Oscillation) prediction models indicate a return to neutral by the end of May, with likely development of La Nina (of unknown strength) by fall," said the IRI analysis posted Thursday, May 12.
The analysis of a declining El Nino, and a quick onset of La Nina, is shared by many in the weather community. And, the timetable of La Nina by fall is moved ahead by some considering how the Pacific is acting. "If (ocean temperature) cooling in the last 30 days is indicative of the future, there will be no El Nino signal by mid-June and I wouldn't be shocked to see La Nina conditions develop by early July," wrote Nebraska associate state climatologist Al Dutcher in an online article posted the week of May 2, 2016.
A switch from very warm to very cool in the equatorial Pacific in a very short period of time -- just a few months -- is hard to compare. Pacific conditions have been tracked for about 125 years, and in that time span, monitoring of the open ocean has a history of only 35 years or so -- following a gigantic El Nino event in 1982. Nonetheless, when one considers the almost-incalculable amount of water involved in the raising or lowering of temperatures, such a move is impressive to say the least.
The effect of La Nina on U.S. crop weather is somewhat disputed, but there is enough evidence, both measured and anecdotally, to make the assertion that La Nina is not favorable to U.S. producers. When La Nina is around, mid- to late-summer conditions can turn hotter and drier. That's obviously a stressful combination for filling corn and soybeans. And, as has been mentioned here before--that's a big reason why I have a yield outlook that has corn and soybeans doing no better than trendline this year.
A key feature to keep track of is soil moisture over the next six weeks. Right now, of course, most crop areas except the northern locales, have favorable moisture -- maybe even too much. If these levels hold through June, it'll go a long way toward helping crops ward off a turn to stressful heat when July rolls around.
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