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ENSO Quick Look IRI ENSO Update / Prediction Technical ENSO Update IRI Probabilistic ENSO Prediction ENSO Prediction Plume Monthly archive ENSO Update15 December 2011SummaryNOTICE: This "IRI ENSO Update/Forecast" is being supplanted by the NOAA/Climate Prediction Center ENSO Diagnostic Discussion, issued early in the month. The IRI Technical ENSO Update is still issued by the IRI near the middle of the month, but the probabilistic ENSO forecast created at mid-month is now an objective rendering directly from the IRI/CPC ENSO prediction plume, using equal weighting for all plume models and using a Gaussian probability density function centered on the multi-model mean prediction. Probabilistic ENSO forecasts having a possibly beneficial subjective component, such as an adjustment when the forecasters believe the models may have biases or may be missing something that occurred very recently, are made jointly by IRI and CPC at the beginning of the month and will be accessible from the NOAA/ Climate Prediction Center's ENSO Diagnostic Discussion beginning in early 2012. Beginning December 2011, the thresholds for El Niño and La Niña are plus and minus 0.5 C Nino3.4 SST anomalies, respectively, as used by NOAA/Climate Prediction Center, rather than the seasonally varying quartile-based values used by IRI up until that time. The implication of the half-degree anomaly thresholds is that non-neutral ENSO conditions are expected to occur with greater than 25% frequency during northern autumn and early winter, and less than 25% frequency during northern spring and early summer.
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