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2016 October Quick Look

Published: October 20, 2016

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)

During mid-October 2016 the tropical Pacific SST anomaly was slightly cooler than -0.5C, the threshold for weak La Niña. However, not all of the atmospheric variables have been supporting weak La Niña conditions for a sufficient duration to constitute good ocean-atmospheric coupling. Although the upper level winds suggest weak La Niña, the lower level trade winds only became stronger than average in mid-September. The Southern Oscillation index and the pattern of cloudiness and rainfall do indicate weak La Niña conditions. The lack of enhanced trade winds until recently makes us hesitate to say La Niña has really begun, so our diagnosis remains ENSO-neutral. The collection of ENSO prediction models indicates SSTs near or slightly cooler than the threshold of La Niña during fall, then weakening to cool-neutral during winter.

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 13, 2016

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 is favored to develop (~70% chance) during the Northern Hemisphere fall 2016 and slightly favored to persist (~55% chance) during winter 2016-17.

ENSO-Neutral conditions were observed during September, with negative sea surface temperatures (SSTs) anomalies expanding across the eastern equatorial Pacific Ocean by early October (Fig. 1). All of the Niño regions cooled considerably during late September and early October, with the latest weekly value of Niño-3.4 index at -0.9°C (Fig. 2). Subsurface temperature anomalies also decreased toward the end of the month (Fig. 3), reflecting the strengthening of below-average temperatures at depth in the east-central equatorial Pacific (Fig. 4). Atmospheric anomalies across the equatorial Pacific edged toward La Niña during September, with a stronger tendency toward La Niña late in the month. The traditional Southern Oscillation index and the equatorial Southern Oscillation index were positive. The lower-level winds were near average across most of the basin during the month, but enhanced easterlies were becoming more persistent west of the International Date Line. Upper-level winds were anomalously westerly near and just east of the International Date Line. Convection was weakly suppressed over the central tropical Pacific and was more enhanced over Indonesia compared to last month (Fig. 5). Overall, the combined ocean and atmosphere system reflects ENSO-Neutral during September, but are more clearly trending toward La Niña conditions.

The multi-model averages favor borderline Neutral-La Niña conditions (3-month average Niño-3.4 index less than or equal to -0.5°C) persisting during the Northern Hemisphere fall and continuing into the winter (Fig. 6 and Fig. 7). Because of the recent cooling in the Niño-3.4 region and signs of renewed atmospheric coupling, the forecaster consensus now favors the formation of a weak La Niña in the near term, becoming less confident that La Niña will persist through the winter. In summary, La Niña is favored to develop (~70% chance) during the Northern Hemisphere fall 2016 and slightly favored to persist (~55% chance) during winter 2016-17 (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 10 November 2016. 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 2016 71% 29% 0%
OND 2016 65% 35% 0%
NDJ 2016 60% 39% 1%
DJF 2017 54% 44% 2%
JFM 2017 44% 51% 5%
FMA 2017 34% 57% 9%
MAM 2017 28% 58% 14%
AMJ 2017 23% 59% 18%
MJJ 2017 20% 58% 22%

IRI ENSO Forecast

IRI Technical ENSO Update

Published: October 20, 2016

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 usually shows stronger anomalies than ERSSTv4, and during very strong events the two datasets may differ by as much as 0.5 C.

Recent and Current Conditions

ENSO-neutral conditions were observed in most ENSO-related variables from May through July 2016. Then in August the average NINO3.4 SST anomaly was -0.54 C, and in September it was -0.59 C, both indicative of a weak La Niña SST condition. For Jul-Sep it was -0.54 C. 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.x, at a weak La Niña level. Accompanying this ocean condition are atmospheric variables that also indicate weak La Niña. However, the lower-level trade winds have been enhanced only for about one month, and have only been enhanced modestly, and mainly only near and west of the date line. Convection anomalies across the equatorial Pacific have been somewhat suggestive of La Niña, and the same is true for the Southern Oscillation Index (SOI). Overall, despite the SST and the roughly consistent atmospheric variables, the diagnosis of weak La Niña is has not yet been made, mainly because the trade wind anomalies have not sufficiently stood the test of time (more than 1 month is desired, and a more eastward-extended swath is desired).

Expected Conditions

What is the outlook for the ENSO status going forward? The most recent official diagnosis and outlook was issued one week ago in the NOAA/Climate Prediction Center ENSO Diagnostic Discussion, produced jointly by CPC and IRI; it carries a La Niña watch and called for a roughly 70% likelihood of La Niña conditions during fall (already underway) 55% for La Niña in winter 2016-17.  The latest set of model ENSO predictions, from mid-October, now available in the IRI/CPC ENSO prediction plume, is discussed below. Currently, the Nino3.4 SST anomalies are at the level of weak La Niña. Subsurface temperature anomalies across the eastern equatorial Pacific continue to be somewhat below average. Slightly enhanced easterly trade winds have been observed in the west-central tropical Pacific, suggestive of La Niña, but not compelling so far. The pattern of sea level pressure (e.g., the SOI), the upper level winds, and the pattern of tropical convection have been more suggestive of La Niña, so that overall, the atmosphere and ocean do appear La Niña-like in mid-October. But the hitch is that these conditions are instantaneous (or, just a mean over one week), and the question of endurance causes some to doubt that the ocean-atmosphere coupling is really in motion. The negative subsurface heat content anomaly may support the extension of the enhanced trades farther east in the tropical Pacific, which would present a more compelling picture of a La Niña. When and if these develop, the SST could remain in the weak La Niña category, or even strengthen somewhat, during the rest of 2016 and into the early part of 2017.  The collection of the latest model predictions suggest that this scenario is about 55-60% likely.

As of mid-October, 62% of the dynamical or statistical models predicts La Niña conditions for the initial Oct-Dec 2016 season, while 38% predict neutral ENSO.  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 2017 season, among models that do use subsurface temperature information, 38% predicts La Niña conditions and 62% predicts ENSO-neutral conditions. For all model types, the probabilities for La Niña are over 60% for Oct-Dec 2016 and Nov-Jan 2017, 46% for Dec-Feb 2016-17, then drop to near 30% for Jan-Mar and drop further to about 10-20% from Feb-Apr to Jun-Aug 2017. The probability for neutral conditions is at least 50% beginning in Dec-Feb 2016-17, and rises to at least 80% from Feb-Apr to Apr-Jun 2017, then drops somewhat for later seasons.  Probabilities for El Niño are near zero until Mar-May 2017, when they rise to 5%, and then up to around 20% for May-Jul and Jun-Aug.

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 at 57% for Oct-Dec 2016, decreasing to 53% for Nov-Jan 2016-17, 47% for Dec-Feb, then droping more quickly and reaching 22% for Feb-Apr 2017, and to less than 20% from Mar-May through Jun-Aug. Probabilities for ENSO-neutral are below 50% through Nov-Jan 2016-17, 51% for Dec-Feb, and higher than 50% through Jun-Aug 2017. Probabilities for ENSO-neutral reach about 80% for Mar-May.  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 likelihood for La Niña conditions near 50-60% for Oct-Dec 2016 and Nov-Jan 2016-17, dropping below 50% for subsequent seasons as the probability for ENSO-neutral rises above 50%.  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 October 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 2016 57% 43% 0%
NDJ 2016 53% 46% 1%
DJF 2017 47% 51% 2%
JFM 2017 35% 63% 2%
FMA 2017 22% 74% 4%
MAM 2017 12% 81% 7%
AMJ 2017 10% 74% 16%
MJJ 2017 15% 61% 24%
JJA 2017 18% 53% 29%

ENSO Forecast

IRI Model-Based Probabilistic ENSO Forecast

Published: October 20, 2016

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 2016 57% 43% 0%
NDJ 2016 53% 46% 1%
DJF 2017 47% 51% 2%
JFM 2017 35% 63% 2%
FMA 2017 22% 74% 4%
MAM 2017 12% 81% 7%
AMJ 2017 10% 74% 16%
MJJ 2017 15% 61% 24%
JJA 2017 18% 53% 29%

ENSO Forecast

CPC Official Probabilistic ENSO Forecast

Published: October 13, 2016

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 2016 71% 29% 0%
OND 2016 65% 35% 0%
NDJ 2016 60% 39% 1%
DJF 2017 54% 44% 2%
JFM 2017 44% 51% 5%
FMA 2017 34% 57% 9%
MAM 2017 28% 58% 14%
AMJ 2017 23% 59% 18%
MJJ 2017 20% 58% 22%

ENSO Forecast

IRI ENSO Predictions Plume

Published: October 20, 2016

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.

List of Models Used

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

Seasons (2016-2017)
Model OND NDJ DJF JFM FMA MAM AMJ MJJ JJA
Dynamical models
NASA GMAO model -0.6 -0.5 -0.4 -0.1 0.1 0.3 0.5
NCEP CFS version 2 -0.9 -1 -1 -0.7 -0.3 -0.1 0.2 0.4
Japan Met. Agency model -0.6 -0.8 -0.9 -0.9 -0.6
Scripps Inst. HCM -1.1 -1.2 -1.2 -1.1 -1 -0.9 -0.7 -0.5 -0.4
Lamont-Doherty model -0.3 -0.2 0 0.2 0.4 0.3 0.2 0 -0.3
POAMA (Austr) model -0.6 -0.6 -0.6 -0.4 -0.3 -0.1 0.1
ECMWF model -0.3 -0.2 -0.1 0 0.1
UKMO model -0.7 -0.7 -0.5 -0.3
KMA (Korea) SNU model -0.6 -0.6 -0.6 -0.6 -0.6 -0.7 -0.7 -0.7 -0.7
IOCAS (China) Intermed. Coupled model -0.8 -0.9 -0.8 -0.7 -0.5 -0.5 -0.5 -0.5 -0.6
COLA CCSM4 model -0.4 -0.5 -0.6 -0.5 -0.3 -0.1 0.1 0.2 0.2
MÉTÉO FRANCE model -0.5 -0.5 -0.4 -0.3 -0.2
Japan Frontier Coupled model -0.5 -0.4 -0.3 -0.2 -0.1 -0.1 0 0.1 0.2
CSIR-IRI 3-model MME -0.2 -0.3 -0.5 -0.5 -0.4 -0.3
GFDL CM2.1 Coupled Climate model -0.8 -0.8 -0.7 -0.4 -0.1 0.3 0.5 0.7 0.9
Canadian Coupled Fcst Sys -0.4 -0.3 -0.1 -0.1 0.1 0.3 0.5 0.8 1.1
GFDL CM2.5 FLOR Coupled Climate model -0.6 -0.5 -0.4 -0.2 -0.1 0.1 0.3 0.6 0.8
Average, dynamical models -0.6 -0.6 -0.5 -0.4 -0.2 -0.1 0 0.1 0.1
Statistical models
NCEP/CPC Markov model -0.6 -0.6 -0.5 -0.4 -0.4 -0.3 -0.3 -0.2 -0.2
NOAA/CDC Linear Inverse -0.3 -0.2 -0.1 -0.1 0 0 0.1 0.1 0.1
NCEP/CPC Constructed Analog -0.6 -0.5 -0.4 -0.3 -0.1 0 0.1 -0.1 -0.1
NCEP/CPC Can Cor Anal -0.4 -0.5 -0.6 -0.5 -0.3 -0.1 0 0 0
Landsea/Knaff CLIPER -0.7 -0.6 -0.5 -0.5 -0.3 -0.2 0 -0.1 -0.2
Univ. BC Neural Network -0.4 -0.3 -0.1 0.1 0.3 0.3 0.4 0.5 0.4
FSU Regression -1 -1 -1 -0.8 -0.5 -0.3 0 0.2 0.4
TCD – UCLA -0.2 0 0.2 0.4 0.5 0.5 0.5 0.6 0.6
UNB/CWC Nonlinear PCA -0.4 -0.3 -0.2 0 0.1 0.1 0.1 0.1 0.2
Average, statistical models -0.5 -0.4 -0.4 -0.2 -0.1 0 0.1 0.1 0.1
Average, all models -0.6 -0.5 -0.5 -0.3 -0.2 -0.1 0.1 0.1 0.1

Discussion of Current Forecasts

The set of dynamical and statistical model predictions issued during late September and early October 2016 predicts either cool-neutral or La Niña conditions during the October-December period. More models suggest weak La Niña than cool-neutral, and this forecast continues through the northern winter season of DJF. Early in 2017, weakening to cool-neutral ENSO conditions is suggested. In the most recent week, the SST anomaly in the Nino3.4 region was -0.x C, at a weak La Niña level, and -0.59 C for the month of September, indicating a weak La Niña SST condition. However, while the atmospheric variables also currently reflect mainly weak La Niña, the trade winds have only been enhanced for about one month and the enhancement has been weak, and therefore the diagnosis of the current ENSO state is unclear and could just as easily be called cool-neutral as weak La Niña.  In fact, the official diagnosis from early October remains neutral. The Southern Oscillation index and the pattern of convection across the tropical Pacific weakly indicate La Niña. Based on the multi-model mean predictions, 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 2016 57% 43% 0%
NDJ 2016 53% 46% 1%
DJF 2017 47% 51% 2%
JFM 2017 35% 63% 2%
FMA 2017 22% 74% 4%
MAM 2017 12% 81% 7%
AMJ 2017 10% 74% 16%
MJJ 2017 15% 61% 24%
JJA 2017 18% 53% 29%

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 20, 2016

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.