WRAL WeatherCenter Blog

Nino or "Nada?"

Posted May 15, 2012

Multi-model forecasts of equatorial east-central Pacific surface temperature departure from normal through early 2013. Values of -.5 or less indicate La Nina conditions, while +.5 or greater represent El Nino.

The La Nina pattern that has been with us for a large portion of the past two years has officially faded now, replaced by "neutral" conditions in the Pacific Ocean in which sea surface temperatures in the central and eastern equatorial regions there have warmed, and are now mainly within +/- one-half degree C of the long-term average value. Now the question is whether we will settle into a long period of neutral conditions sometimes informally referred to as "La Nada," or whether the pendulum will instead swing to the warm side and bring us back to an El Nino regime, in which those Pacific waters exceed the normal levels by .5 degree C or more.

The two images I attached make it apparent that there is no easy answer to that question at the moment. The first graph shows a number of computer models used by climate scientists to predict the state of the Pacific Ocean temperature regime, and if you look closely the spread of the models by the time we reach late summer and early fall is that about half the models indicate a temperature anomaly that tops the +.5-degree mark, while the other half stays cooler than that, but generally warmer than the -.5-degree line.

The second image is the forecast for the coming year from scientists at the Climate Prediction Center and the International Research Institute, and it is pretty much what you'd expect based on the ensemble of computer projections in the previous image. For the next few months, the likelihood of neutral conditions is greater than that of any alternatives, while the late summer and fall feature nearly equal chances that we'll see El Nino or neutral conditions, but a much lesser likelihood that La Nina will make a return appearance.

As uncertain as all of this appears for now, it does have some implications in terms of weather we might experience later in the year and next winter, since (on average) El Nino tends to somewhat suppress hurricane activity in the Atlantic, and also tilts the odds a bit in favor of greater than normal precipitation and lower than normal temperatures through the cooler half of the year for much of the southeast when compared to La Nina or neutral conditions.


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