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Weather’s Transition from El Niño to La Niña


As El Niño changes to La Niña, weather remains the dominant force in agriculture. The temperature of water in the Pacific has signaled the end of El Niño and along with this will come shifts in weather patterns over most of the planet. The change will probably be gradual but forecasters say La Niña will be forming by the end of 2016.

La Niña begins when easterly winds move the warm upper layers of the Pacific westward toward Australia. Water temperature off the South American coast may drop 3 to 4 degrees below the usual levels. “Weather people” noticed that a change was taking place when water temperatures in the eastern Pacific did not change since May, an indication that cooling was about to occur.

The cyclic phenomenon of El Niño and La Niña is known as the Southern Oscillation, and it has been working its magic or mayhem for as long as records have been kept. It is a natural part of our weather. It is far from a regular pattern and is therefore difficult to predict in the long term.

The real issue is how the transition from one part of the cycle to the other will affect weather and agriculture in our region.

The Southern Oscillation influences the jet stream which we have learned has a very strong influence on rainfall patterns all across the nation. Changes in the jet stream also influence the incidence of severe weather and the number of tropical cyclones (we call them hurricanes around here).

As any farmer knows, the incidence of tropical storms often determines both beneficial and harmful weather events in our region. We all can remember years when the only hope we had for late season rain was a tropical storm. Unfortunately these storm can have both good and bad effects depending upon where you are located. History has shown that the likelihood of Atlantic hurricanes is increased during La Niña which will likely be arriving this fall.

During El Niño the jet stream normally is located in an east to west pattern across our region which leads to some of the severe thunderstorms that have occurred during the last few weeks across the Southeast and more recently in our area with winds and hail as we saw last week. During La Niña the jet stream normally moves north, allowing severe weather to move further north also allowing tropical weather to move northward and into our region.

The net global effect caused by the change from El Niño to La Niña is probably not really that great, but it seems very significant since vastly different kinds of weather move into and out of major portions of the nation and around the world.

La Niña probably will not be achieved until after this crop is out of the field, and we will probably continue to receive weather that is commonly associated with El Niño, or frequent and scattered thunderstorms punctuated by days of clear weather into the fall. However, the wise thing to do is to plan on getting the crop out of the field as efficiently as possible, as usual.

The likelihood of rains and fluctuating temperatures may support the development of plant diseases, insects, and weeds. The quality of crops will likely be influenced as well. All the more reason to monitor crops closely to head off these issues before they become severe problems.

If you want to have a better understanding of the way our weather is influenced by the Southern Oscillation there are great sources from NOAA, the National Weather Service, Agroclimate, as well as universities in the Southeast.

Source: Ernie Flint, Michigan State University 

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