Early Evidence Suggests Slow Evolution To La Nina
By Drew Lerner
Kansas City, January 26 (World Weather Inc.) – Recent ocean data from the tropical Pacific continues to suggest that if La Nina is going to evolve this year it is going to be a slow process. World Weather still favors the evolution toward La Nina late this year and not during the growing season, but is quick to admit that the jury is still out on this debate. Confidence is rising “against” an influential La Nina event in the heart of the 2016 growing season.
Evidence is still high of a weakening El Nino this late winter and spring. However, a late season westerly wind burst of size occurred over the central equatorial Pacific Ocean occurred earlier this month that helped to strengthen the El Nino event after already decreasing somewhat. The implication of this strengthening event is no different than that of past El Nino events when there has tended to be a peak of intensity in the late Northern Hemisphere autumn and another in the winter. The anticipated new peak in intensity will not be as intense as the one of earlier this autumn and so the declining trend in El Nino will resume soon after being given this late season insurgence of energy to perpetuate a little longer.
In the meantime, there is still a growing pool of colder than usual ocean water building up beneath the surface of the ocean “west” of the International Dateline. The pooling of sub-surface cooler than usual ocean water temperatures is a natural phenomenon that occurs in mature El Nino events and it becomes a seedling to what eventually ends the El Nino event. Sometimes when the pooling cold water is frequently reinforced by more cold water the potential for La Nina can evolve, but, so far, the pooling of cold water has not been great enough to give World Weather, Inc. much reason to expect a quick transition to La Nina.
The world is anxiously anticipating the arrival of La Nina and some forecasters have already suggested that weather conditions around the world will become more adverse as the La Nina unfolds. Of course there is no need to point out that we heard the same thing when El Nino evolved and the predictions of the “most adverse El Nino on record” broadcast by our alarmists friends fell flat on its face.
From a purely scientific viewpoint, evidence for a quick translation from El Nino to La Nina seems sparse and the odds are more in favor of neutral ENSO conditions this summer than they are favoring La Nina, but there is still time for this to change. One very important comment needs to be made and that is to remember that dryness problems in the United States and other mid-latitude locations is not driven by La Nina alone. Please remember that there are other weather patterns prevailing behind ENSO events and they can sometimes have much to say about weather even while El Nino or La Nina are in place.
A perfect example of this is 1983. The El Nino event of 1982-83 behaved quite similarly to that of this year and yet La Nina did not evolve until 1984. Nevertheless, U.S. weather suffered greatly from too much rain and coolness in the spring 1983 followed by a sudden shift to dry and warm weather in July and August 1983 and the combination of cool and wet followed by hot and dry was a big drop in production. Crop genetics were different back then, but a similar type scenario may play out this spring and summer, although a repeat of 1983 is highly unlikely.
There have been other El Nino events, both weak and strong, that have evolved to neutral ENSO conditions and not La Nina and there have been a few that weakened to weak El Nino events that lingered for several months after the primary El Nino event had dissipated. Both scenarios still have potential to be seen in 2016, along with the potential for La Nina. World Weather, Inc. prefers the neutral ENSO scenario for summer 2016.
The strongest non-ENSO weather influence on U.S. weather in 2016 will be a tendency for the southern U.S. Plains to be drier and warmer than usual. Confidence is high on this potential. There is some evidence for dry and less warm conditions occurring in the Delta and lower Ohio River Valley while there is also some weak support for cooler-biased temperatures and restricted rainfall in the southeastern states.
The most fascinating part of the U.S. outlook for this spring and summer is the impressive contrast in past occurrences of strong El Nino to La Nina and strong El Nino to neutral ENSO conditions of the past. In the past, strong El Nino to La Nina events between January and July have resulted in warmer than usual temperatures in most U.S. crop areas east of the high Plains region for May through August while precipitation was below average in the central and southern Plains, Delta and southeastern states. This trend for drier-biased conditions in the southern states matches well with a long term weather pattern that is due to repeat this summer in the same areas with or without La Nina. The presence of this other long term trend makes a La Nina year of greater significance because the two weather trends would combine to produce a very strong signal for dryness in the southern states. However, the evidence for La Nina is not great enough to buy into this scenario – at least not now.
Contrasting with the strong El Nino to La Nina scenario, noted above, the translation from strong El Nino in January to neutral ENSO conditions in July usually results in cooler biased temperatures in much of the eastern U.S. and precipitation that is below average from Illinois and Iowa to the southern Plains. The biggest difference here in these two scenarios is the cooler bias which tends to dominate May and June with some tendency for March and April to be cool, as well. In four different cases, the El Nino to Neutral ENSO years resulted in less crop stress because of the cool bias. 1983 is the only year that bucks the trend and it may have been more of a fluke with an unexpected strong high pressure ridge evolving in the middle of the nation that year causing more problems with heat in the second half of summer and reducing rain faster than in other years. A repeat of 1983 would be considered very unlikely, but a scenario similar to that year cannot be ruled out.
The past 90 days of weather has looked strangely like that of 1982-83 and if World Weather, Inc. is correct about strong El Nino to neutral ENSO conditions this year the odds are high that a cooler biased spring will occur, especially in the lower Midwest, Delta, southern Plains and southeastern states. These areas will also be impacted by frequent storm systems and wet field conditions. The result of which is likely to be delayed spring planting. 1983 was not the only El Nino to neutral ENSO year that produced this colder bias and there is more evidence that this may be the correct trend with the recent evolution of negative arctic oscillation (AO) and the potential for more of the same during the last days of winter and spring.
Both 1983 and 1998 had significantly wet spring seasons and since these were to other strong El Nino events of the past this trend for wetter biases needs to be closely monitored.
In the meantime, World Weather, Inc. will continue closely monitoring ocean temperature changes in the next few weeks. Computer forecast models are very reliable in predicting ocean temperature changes about three months in advance and when March rolls around we will be able to peer into the future (through June) with a high level of confidence to see) what the fate of El Nino will likely be and whether or not a translation to La Nina is expected or not during the growing season. World Weather, Inc. is placing its bets on neutral ENSO this growing season with La Nina possible in late in the third quarter or more likely the 4th quarter of this year resulting in tropical influences around the world turning notably wetter biased at that time with other changes reaching the middle latitudes in 2017.
While we wait on the final determination of La Nina or no La Nina, preparations should be made for a wet spring in the lower Midwest, Delta, interior southeastern U.S. and a part of the southern Plains with dryness in the northwestern Plains and western Canada while a more normal precipitation bias occurs in the northern Midwest and northeastern Plains. Temperatures will be cool this late winter and spring in the southeastern states and possibly a fair amount of the lower Midwest, Delta and southern Plains. Western Canada will be warmest and driest relative to normal this late winter and spring with Alberta and Montana already carrying moisture deficits they will likely be first to experience moisture shortages in the coming growing season.
One last consideration needs to be made from the “what if” department and that is what if El Nino lingers longer into the summer than expected. In that case, the potential would be another summer of timely rainfall and more reason to expect favorable crop development in the United States. This scenario would still have to be played against the long term prevailing weather patterns supporting less than usual southern U.S. precipitation during the summer. On a more negative note, continued El Nino conditions this summer might not bode well for western Canada’s Prairies and Montana where drought might be a bigger consideration.
In both the El Nino to neutral ENSO and continued El Nino scenarios for 2016, the likely impact on the long-term pattern favoring dryness in the southern United States this summer would be to minimize that dryness and provide a more favorable production year. That places all the pressure on a potentially problematic growing season for the U.S. totally on the prospects of La Nina. Without La Nina, the summer season may be more favorable than detrimental for production in 2016. With that said, keep in mind the potential concerns resulting from a wet and cool-biased spring….that may happen regardless of any of the various scenarios for summer.
In the meantime, western Canada may face prolonged dryness if El Nino prevails too long, but neutral ENSO conditions might offer some dryness relief. The best scenario for the Canadian Prairies weather would be El Nino to La Nina in which the drier areas of the western Prairies would be replaced by frequent rainfall during the summer. Without La Nina there will be less rain, but only in the case of continued El Nino would there be more concern for more notable dryness in the west.
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