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2017 October Quick Look

Published: October 19, 2017

A monthly summary of the status of El Niño, La Niña, and the Southern Oscillation, or ENSO, based on the NINO3.4 index (120-170W, 5S-5N)

In mid-October 2017, the tropical Pacific remained in an ENSO-neutral state but near the borderline of weak La Niña, as SSTs in the east-central tropical Pacific have cooled to the threshold for La Niña and the atmosphere has also shown patterns suggestive of near-La Niña conditions. The collection of latest ENSO prediction models indicates weak La Niña as a likely scenario during Northern Hemisphere fall and winter. The official CPC/IRI outlook favors La Niña development, and carries a La Niña watch.

Figures 1 and 3 (the official CPC ENSO probability forecast and the objective model-based IRI ENSO probability forecast, respectively) are often quite similar. However, occasionally they may differ noticeably. There can be several reasons for differences. One possible reason is that the human forecasters, using their experience and judgment, may disagree to some degree with the models, which may have known biases. Another reason is related to the fact that the models are not run at the same time that the forecasters make their assessment, so that the starting ENSO conditions may be slightly different between the two times. The charts on this Quick Look page are updated at two different times of the month, so that between the second and the third Thursday of the month, the official forecast (Fig. 1) has just been updated, while the model-based forecasts (Figs. 3 and 4) are still from the third Thursday of the previous month. On the other hand, from the third Thursday of the month until the second Thursday of the next month, the model-based forecasts are more recently updated, while the official forecasts remain from the second Thursday of the current month.
Click on the for more information on each figure.

Historically Speaking

    El Niño and La Niña events tend to develop during the period Apr-Jun and they
  • Tend to reach their maximum strength during October - February
  • Typically persist for 9-12 months, though occasionally persisting for up to 2 years
  • Typically recur every 2 to 7 years

ENSO Forecast

CPC ENSO Update

Published: October 12, 2017

El Niño/Southern Oscillation (ENSO) Diagnostic Discussion issued by the Climate Prediction Center/NCEP/NWS

ENSO Alert System Status: La Niña Watch

Synopsis: La Niña conditions are favored (~55-65%) during the Northern Hemisphere fall and winter 2017-18.

During September, ENSO-neutral conditions were reflected in near-to-below average sea surface temperatures (SSTs) across most of the central and eastern Pacific Ocean (Fig. 1). The weekly Niño indices were volatile during the month, with negative values increasing to near zero during the past week in the Niño-4, Niño-3.4, and Niño-3 regions (Fig. 2). In contrast, sub-surface temperature anomalies were increasingly negative during September (Fig. 3), reflecting the shallow depth of the thermocline across the central and eastern Pacific (Fig. 4). Also, convection was suppressed near the International Date Line and enhanced near Indonesia (Fig. 5). Over the western equatorial Pacific Ocean, low-level trade winds were anomalously easterly and upper-level winds were anomalously westerly.  Overall, the ocean and atmosphere system remains consistent with ENSO-neutral, although edging closer to La Niña conditions.

For the upcoming Northern Hemisphere fall and winter 2017-18, a weak La Niña is favored in the dynamical model averages of the IRI/CPC plume (Fig. 6). Several models indicate a period of near-average Niño-3.4 values in the upcoming weeks, but then predict reinvigorated growth of negative SST anomalies across the equatorial Pacific Ocean.  These forecasts are supported by the ongoing easterly wind anomalies across portions of the Pacific Ocean and the reservoir of below-average subsurface temperatures.  In summary, La Niña conditions are favored (~55-65%) during the Northern Hemisphere fall and winter 2017-18  (click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).

This discussion is a consolidated effort of the National Oceanic and Atmospheric Administration (NOAA), NOAA’s National Weather Service, and their funded institutions. Oceanic and atmospheric conditions are updated weekly on the Climate Prediction Center web site (El Niño/La Niña Current Conditions and Expert Discussions). Forecasts are also updated monthly in the Forecast Forum section of CPC’s Climate Diagnostics Bulletin. Additional perspectives and analysis are also available in an ENSO blog.

The next ENSO Diagnostics Discussion is scheduled for 9 November 2017. To receive an e-mail notification when the monthly ENSO Diagnostic Discussions are released, please send an e-mail message to: ncep.list.enso-update@noaa.gov.

Climate Prediction Center
National Centers for Environmental Prediction
NOAA/National Weather Service
College Park, MD 20740

CPC/IRI Early-Month Official ENSO Forecast Probabilities

Season La Niña Neutral El Niño
SON 2017 53% 47% 0%
OND 2017 63% 37% 0%
NDJ 2017 66% 33% 1%
DJF 2017 67% 32% 1%
JFM 2018 60% 38% 2%
FMA 2018 47% 48% 5%
MAM 2018 32% 57% 11%
AMJ 2018 23% 61% 16%
MJJ 2018 18% 59% 23%

IRI ENSO Forecast

IRI Technical ENSO Update

Published: October 19, 2017

Note: The SST anomalies cited below refer to the OISSTv2 SST data set, and not ERSSTv4. OISSTv2 is often used for real-time analysis and model initialization, while ERSSTv4 is used for retrospective official ENSO diagnosis because it is more homogeneous over time, allowing for more accurate comparisons among ENSO events that are years apart. During ENSO events, OISSTv2 often shows stronger anomalies than ERSSTv4, and during very strong events the two datasets may differ by as much as 0.5 C. Additionally, the ERSSTv4 may tend to be cooler than OISSTv2, because ERSSTv4 is expressed relative to a base period that is updated every 5 years, while the base period of OISSTv2 is updated every 10 years and so, half of the time, is based on a slightly older period and does not account as much for the slow warming trend in the tropical Pacific SST.

Recent and Current Conditions

In mid-October 2017, the NINO3.4 SST anomaly was near the borderline of the weak La Niña category. For September the SST anomaly was -0.47 C, in the upper portion of the ENSO-neutral range, and for July-September it was -0.07 C, in the ENSO-neutral range. The IRI’s definition of El Niño, like NOAA/Climate Prediction Center’s, requires that the SST anomaly in the Nino3.4 region (5S-5N; 170W-120W) exceed 0.5 C. Similarly, for La Niña, the anomaly must be -0.5 C or less. The climatological probabilities for La Niña, neutral, and El Niño conditions vary seasonally, and are shown in a table at the bottom of this page for each 3-month season. The most recent weekly anomaly in the Nino3.4 region was -0.5, at the borderline of ENSO-neutral and weak La Niña. The pertinent atmospheric variables, including the upper and lower level zonal wind anomalies, have been showing patterns suggestive of near-La Niña, and he Southern Oscillation Index (SOI) has also been somewhat above average. Subsurface temperature anomalies across the eastern equatorial Pacific are somewhat below average. Despite recent SST anomalies and some clear signs of La Niña patterns in some key atmospheric variables, the combination of the SST and the atmospheric conditions continues to warrant an official diagnosis of ENSO-neutral for the recent 1-month period.

Expected Conditions

What is the outlook for the ENSO status going forward? The most recent official diagnosis and outlook was issued approximately one week ago in the NOAA/Climate Prediction Center ENSO Diagnostic Discussion, produced jointly by CPC and IRI; it stated that La Niña is favored for fall and into winter, with slightly lower chances for ENSO-neutral. A La Niña watch was issued with that Discussion, for the second consecutive month. The latest set of model ENSO predictions, from mid-October, now available in the IRI/CPC ENSO prediction plume, is discussed below. Those predictions suggest that the SST has the greatest chance for being in the weak La Niña range for October-December through January-March 2017, with a slightly lower but significant probability for ENSO-neutral during that period.

As of mid-October, about 65 to 70% of the dynamical or statistical models predicts La Niña conditions from the initial Oct-Dec 2017 season through to the Jan-Mar 2018 season. During this period, about 30 to 35% of models predict neutral conditions, while no models predicts El Niño conditions. At lead times of 3 or more months into the future, statistical and dynamical models that incorporate information about the ocean’s observed subsurface thermal structure generally exhibit higher predictive skill than those that do not. For the Jan-Mar 2018 season, among models that do use subsurface temperature information, 33% of models predicts neutral conditions and 67% predicts La Niña conditions. For all models, at longer lead times reaching through the first half of 2018, predictions for ENSO-neutral conditions dominate, with probabilities from 70% to higher levels, except for the final season of Jun-Aug 2018 when the probability for El Niño rises to 35% and for La Niña decreases to near zero.

Note  – Only models that produce a new ENSO prediction every month are included in the above statement.

Caution is advised in interpreting the distribution of model predictions as the actual probabilities. At longer leads, the skill of the models degrades, and skill uncertainty must be convolved with the uncertainties from initial conditions and differing model physics, leading to more climatological probabilities in the long-lead ENSO Outlook than might be suggested by the suite of models. Furthermore, the expected skill of one model versus another has not been established using uniform validation procedures, which may cause a difference in the true probability distribution from that taken verbatim from the raw model predictions.

An alternative way to assess the probabilities of the three possible ENSO conditions is more quantitatively precise and less vulnerable to sampling errors than the categorical tallying method used above. This alternative method uses the mean of the predictions of all models on the plume, equally weighted, and constructs a standard error function centered on that mean. The standard error is Gaussian in shape, and has its width determined by an estimate of overall expected model skill for the season of the year and the lead time. Higher skill results in a relatively narrower error distribution, while low skill results in an error distribution with width approaching that of the historical observed distribution. This method shows probabilities for La Niña between 65 and 70% from Oct-Dec to Dec-Feb, with 30-35% probabilities for neutral conditions during these seasons and near-zero probabilities for El Niño. Probabilities for ENSO-neutral rise to approximately 75% during Mar-May and Apr-Jun when the likely La Niña conditions are expected to have returned to neutral. For the longer lead forecasts for Apr-Jun to Jun-Aug 2018, chances for El Niño rise to 32% by the final season as chances for neutral remain greater than 50% and for La Niña decrease to 15-20%. A plot of the probabilities generated from this most recent IRI/CPC ENSO prediction plume using the multi-model mean and the Gaussian standard error method summarizes the model consensus out to about 10 months into the future. The same cautions mentioned above for the distributional count of model predictions apply to this Gaussian standard error method of inferring probabilities, due to differing model biases and skills. In particular, this approach considers only the mean of the predictions, and not the total range across the models, nor the ensemble range within individual models.

In summary, the probabilities derived from the models on the IRI/CPC plume describe, on average, a preference for weak La Niña conditions from Oct-Dec 2017 to Jan-Mar 2018, with neutral regaining highest probability status from Feb-Apr through the end of the forecast period in summer 2018. Chances for El Niño are very small through Mar-May 2018, rising to near-climatological probabilities for May-Jul and slightly higher for Jun-Aug 2018. A caution regarding this latest set of model-based ENSO plume predictions, is that factors such as known specific model biases and recent changes that the models may have missed will be taken into account in the next official outlook to be generated and issued in early June by CPC and IRI, which will include some human judgement in combination with the model guidance.

Climatological Probabilities

Season La Niña Neutral El Niño
DJF 36% 30% 34%
JFM 34% 38% 28%
FMA 28% 49% 23%
MAM 23% 56% 21%
AMJ 21% 58% 21%
MJJ 21% 56% 23%
JJA 23% 54% 23%
JAS 25% 51% 24%
ASO 26% 47% 27%
SON 29% 39% 32%
OND 32% 33% 35%
NDJ 35% 29% 36%

 

IRI ENSO Forecast Histogram Image

IRI/CPC Mid-Month Model-Based ENSO Forecast Probabilities

Season La Niña Neutral El Niño
OND 2017 67% 33% 0%
NDJ 2017 70% 30% 0%
DJF 2018 67% 33% 0%
JFM 2018 57% 42% 1%
FMA 2018 41% 58% 1%
MAM 2018 22% 75% 3%
AMJ 2018 16% 73% 11%
MJJ 2018 15% 61% 24%
JJA 2018 16% 52% 32%

ENSO Forecast

IRI Model-Based Probabilistic ENSO Forecast

Published: October 19, 2017

A purely objective ENSO probability forecast, based on regression, using as input the model predictions from the plume of dynamical and statistical forecasts shown in the ENSO Predictions Plume. Each of the forecasts is weighted equally. It is updated near or just after the middle of the month, using forecasts from the plume models that are run in the first half of the month. It does not use any human interpretation or judgment. This is updated on the third Thursday of the month.

IRI ENSO Forecast Histogram Image

IRI/CPC Mid-Month Model-Based ENSO Forecast Probabilities

Season La Niña Neutral El Niño
OND 2017 67% 33% 0%
NDJ 2017 70% 30% 0%
DJF 2018 67% 33% 0%
JFM 2018 57% 42% 1%
FMA 2018 41% 58% 1%
MAM 2018 22% 75% 3%
AMJ 2018 16% 73% 11%
MJJ 2018 15% 61% 24%
JJA 2018 16% 52% 32%

ENSO Forecast

CPC Official Probabilistic ENSO Forecast

Published: October 12, 2017

The official CPC ENSO probability forecast, based on a consensus of CPC and IRI forecasters. It is updated during the first half of the month, in association with the official CPC ENSO Diagnostic Discussion. It is based on observational and predictive information from early in the month and from the previous month. It uses human judgment in addition to model output, while the forecast shown in the Model-Based Probabilistic ENSO Forecast relies solely on model output. This is updated on the second Thursday of every month.

NOAA?CPC ENSO Forecast Image
NOAA/CPC ENSO Forecast Graphic, courtesy of NOAA/CPC

CPC/IRI Early-Month Official ENSO Forecast Probabilities

Season La Niña Neutral El Niño
SON 2017 53% 47% 0%
OND 2017 63% 37% 0%
NDJ 2017 66% 33% 1%
DJF 2017 67% 32% 1%
JFM 2018 60% 38% 2%
FMA 2018 47% 48% 5%
MAM 2018 32% 57% 11%
AMJ 2018 23% 61% 16%
MJJ 2018 18% 59% 23%

ENSO Forecast

IRI ENSO Predictions Plume

Published: October 19, 2017

Note on interpreting model forecasts

The following graph and table show forecasts made by dynamical and statistical models for SST in the Nino 3.4 region for nine overlapping 3-month periods. Note that the expected skills of the models, based on historical performance, are not equal to one another. The skills also generally decrease as the lead time increases. Thirdly, forecasts made at some times of the year generally have higher skill than forecasts made at other times of the year--namely, they are better when made between June and December than when they are made between February and May. Differences among the forecasts of the models reflect both differences in model design, and actual uncertainty in the forecast of the possible future SST scenario.

Interactive Chart

You can highlight a specific model by hovering over it either on the chart or the legend. Selecting An item on the legend will toggle the visibility of the model on the page. You can also select DYN MODELS or STAT MODELS to toggle them all at once. Clicking on the "burger" menu above the legend will give you options to download the image or expand to full screen. If you have any feedback on this new feature, please let us know at webmaster@iri.columbia.edu.

Notice about the NASA-GMAO model ENSO forecasts

GMAO staff discovered a mistake in the calculation of ensemble mean fields that resulted in an under-representation of ensemble spread and an over-representation of error in the ensemble mean. The mistake impacts forecasts from Feb 2017 through July 2019, and has been corrected as of August 2019. All forecasts hence will have the correct fields. We have not corrected any previous forecast output sent to IRI. If you need the retroactive corrected fields, please contact GMAO at: anna.borovikov@nasa.gov, kazumi.nakada@nasa.gov

List of Models Used

Forecast SST Anomalies (deg C) in the Nino 3.4 Region

Seasons (2017-2018)
Model OND NDJ DJF JFM FMA MAM AMJ MJJ JJA
Dynamical models
NASA GMAO model -1 -1.1 -1.1 -1 -0.8 -0.6 -0.4
NCEP CFS version 2 -0.7 -0.9 -1.3 -1.4 -1.2 -0.8 -0.5 -0.3
Japan Met. Agency model -0.8 -1 -1 -0.9 -0.6
Beijing Climate Center BCC-CSM1.1M -0.8 -0.8 -0.6 -0.3 0 0.2 0.4 0.6 0.7
King Abdulaziz University (Saudi Arabia) -0.6 -0.5 -0.4 -0.2 0 0.2 0.3 0.4 0.6
Lamont-Doherty model -0.5 -0.5 -0.4 -0.1 0.2 0.4 0.5 0.6 0.6
POAMA (Austr) model -0.6 -0.8 -0.7 -0.6 -0.4 -0.3 -0.1
ECMWF model -0.8 -0.8 -0.7 -0.5 -0.4
UKMO model -1.1 -1.2 -1.1 -0.8
KMA (Korea) SNU model -0.5 -0.4 -0.3 -0.3 -0.2 -0.2 -0.2 -0.2 -0.2
IOCAS (China) Intermed. Coupled model -0.3 -0.5 -0.5 -0.3 -0.2 -0.1 0 0.1 0.2
COLA CCSM4 model -0.4 -0.8 -1.1 -1.1 -0.9 -0.6 -0.4 -0.2 -0.3
MÉTÉO FRANCE model -1.1 -1.2 -1.2 -1 -0.9
Japan Frontier Coupled model -0.6 -0.6 -0.5 -0.5 -0.4 -0.4 -0.4 -0.3 -0.2
CSIR-IRI 3-model MME -0.3 -0.4 -0.7 -0.7 -0.6 -0.4
GFDL CM2.1 Coupled Climate model -1.2 -1.3 -1 -0.6 -0.2 0.2 0.5 0.8 1.2
Canadian Coupled Fcst Sys -0.6 -0.7 -0.7 -0.5 -0.3 -0.1 0.2 0.5 0.7
GFDL CM2.5 FLOR Coupled Climate model -0.9 -0.9 -0.7 -0.6 -0.4 -0.1 0.2 0.5 0.8
Average, dynamical models -0.7 -0.8 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4
Statistical models
PSD-CIRES(CU) LIM -0.5 -0.5 -0.4 -0.4 -0.4 -0.4 -0.3 -0.2 -0.2
NCEP/CPC Markov model -0.8 -0.7 -0.6 -0.5 -0.4 -0.4 -0.3 -0.2 -0.2
NCEP/CPC Constructed Analog 0 0 0 -0.1 -0.1 0.1 0.2 0.1 0
Landsea/Knaff CLIPER -0.5 -0.4 -0.4 -0.3 -0.3 -0.2 -0.2 -0.3 -0.4
Univ. BC Neural Network -0.7 -0.8 -0.7 -0.6 -0.4 -0.3 -0.1 0.1 0.2
FSU Regression -0.6 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0
TCD – UCLA -0.6 -0.6 -0.6 -0.6 -0.5 -0.4 -0.4 -0.4 -0.4
Average, statistical models -0.5 -0.5 -0.5 -0.4 -0.4 -0.3 -0.2 -0.1 -0.1
Average, all models -0.7 -0.7 -0.7 -0.6 -0.4 -0.2 -0.1 0.1 0.2

Discussion of Current Forecasts

Most of the models in the set of dynamical and statistical model predictions issued during early October 2017 predicts  weak La Niña conditions during the period of October-December 2017 to January-March 2018 period.  In the most recent week, the SST anomaly in the Nino3.4 region was -0.5 C, at the borderline of weak La Niña, and -0.47 C for the month of September, also near that borderline.  The key atmospheric variables now also suggest borderline or weak La Niña patterns.  Based on the multi-model mean prediction, and the expected skill of the models by start time and lead time, the probabilities (X100) for La Niña, neutral and El Niño conditions (using -0.5C and 0.5C thresholds) over the coming 9 seasons are:

IRI/CPC Mid-Month Model-Based ENSO Forecast Probabilities

Season La Niña Neutral El Niño
OND 2017 67% 33% 0%
NDJ 2017 70% 30% 0%
DJF 2018 67% 33% 0%
JFM 2018 57% 42% 1%
FMA 2018 41% 58% 1%
MAM 2018 22% 75% 3%
AMJ 2018 16% 73% 11%
MJJ 2018 15% 61% 24%
JJA 2018 16% 52% 32%

Summary of forecasts issued over last 22 months

The following interactive plot shows the model forecasts issued not only from the current month (as in the plot above), but also from the 21 months previous to this month. The observations are shown up to the most recently completed 3-month period. The plots allow comparison of plumes from the previous start times, or examination of the forecast behavior of a given model over time.
Hovering over any single model will highlight that particular model in the chart.
Clicking a particular model will hide/show that model in the chart.
At the bottom of the plot, you can select which models to show in the chart: all the models, the dynamical models only, or the statistical models only.

Notes on the data 

Only models producing forecasts on a monthly basis are included. This means that some models whose forecasts appear in the Experimental Long-Lead Forecast Bulletin (produced by COLA) do not appear in the table.

Once an IRI ENSO probability forecast has been published, the results stand even if a model reports an error and changes their data. When this happens we will update the plume with the model's correct values even though our forecast hasn't changed. What this means is that our forecast is always the same, but the underlying data may be different from what we based our forecast on.

The SST anomaly forecasts are for the 3-month periods shown, and are for the Nino 3.4 region (120-170W, 5N-5S). Often, the anomalies are provided directly in a graph or a table by the respective forecasting centers for the Nino 3.4 region. In some cases, however, they are given for 1-month periods, for 3-month periods that skip some of the periods in the above table, and/or only for a region (or regions) other than Nino 3.4. In these cases, the following means are used to obtain the needed anomalies for the table:

  • Temporal averaging
  • Linear temporal interpolation
  • Visual averaging of values on a contoured map

The anomalies shown are those with respect to the base period used to define the normals, which vary among the groups producing model forecasts. They have not been adjusted to anomalies with respect to a common base period. Discrepancies among the climatological SST resulting from differing base periods may be as high as a quarter of a degree C in the worst cases. Forecasters are encouraged to use the standard 1991-2020 period as the base period, or a period not very different from it.

Historical SST Anomalies Image

ENSO Forecast

Forecast Probability Distribution Based on the IRI ENSO Prediction Plume

Published: October 19, 2017

The plots on this page show predictions of seasonal (3-month average) sea surface temperature (SST) anomaly in the Niño3.4 region in the east-central tropical Pacific (5°N-5°S, 120°-170°W), covering the nine overlapping seasons beginning with the current month. The predictions are based on the large (20+) set of dynamical and statistical models in the plume of model ENSO predictions.

  • Model Based Prediction Percentiles Image

    Figure 5

    Predictions of ENSO are probabilistic. The ensemble mean prediction is only a best single guess. On either side of that prediction, there is a substantial uncertainty distribution, or error tolerance. The second plot (Figure 2) shows the estimated probability distribution of the predictions, showing a set of percentiles within that distribution for each lead time. The distribution is modeled as a normal (Gaussian) distribution, so that the overall mean forecast represents the center, or 50 percentile, in the distribution. The overall mean is formed using equal weighting among all models. On either side, other percentile values are shown symmetrically, ranging from 1 to 99 and including some intermediate percentiles (5 and 95, 15 and 85, and 25 and 75). The plot enables a user to estimate the probability of the Niño3.4 SST anomaly to be greater or less than some critical value, or within some interval. If, for example, the 85 percentile falls at 1.8° C above average, the probability of the SST exceeding 1.8° C can be estimated at 15%. Probabilities for exceeding or not exceeding values not exactly on percentile line can be roughly interpolated by eye. The overall width of the probability distribution is derived from the historical skill of the hindcasts of the models, from 1982 to present, for the specific forecast start time and lead time. This method of defining the probability distribution represents one of two general approaches, the other approach being a direct counting of ensemble members within each of the percentile bands. This second approach assumes that the ensemble spreads of the models are true representations of the uncertainty. Individual model spreads have often been found to be somwehate narrower than they should be, although in multi-model ensembles this tendency has been shown to be milder or even eliminated.

  • Model Based Prediction Distribution Image

    Figure 6

    Figure 6, sometimes called a spaghetti diagram, shows synthetically generated prediction scenarios that are equally likely. Here, 100 scenarios are shown; any number can be generated for such a diagram. Each scenario is produced using a random number generator, combined with knowledge of the mean forecast and its uncertainty, as well as the amount of persistence of anomalies. The degree of persistence of anomalies is based on the correlation of prediction errors from one lead time to another. In other words, the individual lines are designed to show the correct amount of persistence as expected in nature, rather than jumping around more randomly from one lead time to the next. The uncertainty and persistence statistics are based on the set of 7 NMME (North American Multimodel Ensemble) models, as it is assumed that these statistics are approximately applicable to all of the models. Sometimes the “spaghetti density” may appear asymmetric about the mean of all the forecasts or outside of the 85 and 15 percentile lines. This is purely sampling variability, and would not occur if many thousands of such lines were plotted. But with that many lines, most of the plot would be too crowded to get a sense of the behavior of the lines near the center of the distribution. The main purpose of the diagram is to serve users who want to assess realistic individual scenarios of ENSO behavior rather than statistical summaries of the forecast like the percentiles shown in the second plot.

The CPC ENSO forecast is released at 9am (Eastern Time) on the second Thursday of each month.

The IRI ENSO forecast is released on the 19th of each month. If the 19th falls on a weekend or holiday, it is released on the closest business day.

All data from this website is covered under the Creative Commons Attribution 4.0 License. When citing IRI ENSO images or data, please use "Images [or Data] provided by The International Research Institute for Climate and Society, Columbia University Climate School", with a link to https://iri.columbia.edu/ENSO.