El Niño conditions are officially underway in the Equatorial Pacific Ocean as of June 2026, and confidence continues to grow that this will be a "very strong" or "super" El Niño event, possibly challenging all-time records in terms of sea surface temperature anomalies dating back to the 1800s.

What is El Niño?

The term El Niño refers to the large-scale ocean-atmosphere climate phenomenon linked to periodic warming in sea-surface temperatures across the central and eastern equatorial Pacific.

El Niño represents the warm phase of the ENSO cycle and means that the ocean water temperatures are warmer than average.

El Niño Strength Thresholds:

There are multiple methods and indices for determining the strength of an El Niño episode. Most indices measure sea surface temperature (SST) anomalies in various regions of the Eastern Equatorial Pacific Ocean.

For historical comparisons, SST anomalies in the Niño 3.4 region are most often evaluated.

In the past, this has contributed to the Oceanic Niño Index (ONI), which measures the 3-month average sea surface temperature anomaly in the Niño 3.4 region.

Starting in 2026, NOAA and other meteorological agencies around the world adopted the Relative Oceanic Niño Index (RONI) as the new standard. RONI takes the original Nino 3.4 region SST anomaly and subtracts the overall global tropical SST anomaly (i.e. the entire ocean area between 20º North and 20º South latitude).

Looking back historically, the difference between ONI and RONI values is relatively minor in most years, but it does make a difference in El Niño or La Niña strength and in neutral vs. El Niño or La Niña classifications in some years.

In the image below, showing historical ENSO data back to 1950, the first chart shows a time series of both ONI (in red) and RONI (in blue) with positive values (> 0.5ºC) indicating El Niño episodes and negative values (-0.5ºC) indicating La Niña episodes. The second chart shows the difference between the two (ONI minus RONI).

NOAA's reasoning for adopting the RONI index is to better account for changes in global tropical sea surface temperatures, whereas ONI only measures against 30-year averages that are updated once every 10 years, and may not pick up on shorter-term changes in global sea surface temperatures. 

Learn More → Relative Oceanic Niño Index (RONI)

Regardless of whether you look at the RONI or ONI Index, the ENSO thresholds remain the same for evaluating events.

El Niño Strength (Based on Niño 3.4 SST Anomaly):

• Neutral: Anomaly of < 0.5ºC
• Weak El Niño: Anomaly of 0.5º to 1.0ºC
• Moderate El Niño: Anomaly of 1.0 to 1.5ºC
• Strong El Niño: Anomaly of 1.5 to 2.0ºC
• Super El Niño: Anomaly > 2.0ºC

The classifications for La Niña (the cool phase of the ENSO Cycle) are similar, but for negative (cool) SST anomalies instead of positive anomalies.

Current El Niño Status as of June 2026:

NOAA has declared that El Niño conditions are officially present in the Equatorial Pacific Ocean. The transition has happened quickly, as La Niña conditions were present from January to March 2026. Since then, sea surface temperatures in the ENSO region have warmed rapidly, a sign of a developing strong (or super) El Niño.

In the image below, the red colors indicate sea surface temperature anomalies. Along the equator in the Pacific Ocean, the warm signature is very evident, especially just off the coast of South America.

This El Niño event is emerging as an "easterly based" El Niño, meaning that sea surface temperatures are highest just off the coast of South America, or in the Niño 1+2 region. 

As of June 15, these are the current SST anomalies in the ENSO regions of the Pacific. While warming is strongest in the eastern (1+2) region, warming is well underway in the central Pacific (Nino 3.4) region and all other ENSO regions as well.

Compared to past emerging El Ninos, the sea surface temperature profile is similar to where we were in June 2023.

However, the rate of warming is faster this year, as we did not transition out of a La Niña in the Central Pacific until April of 2026, whereas it happened in March of 2023 (this was also a La Niña to El Niño transition year).

In fact, sea surface temperatures in the Niño 3.4 region are warming at a faster rate this year compared to the spring/summer of the previous two super El Niño years of 2015 and 1997.

El Niño Forecast for Summer, Fall, and Winter (2026-2027):

We feel very confident in saying that El Niño conditions are going to prevail through the fall and winter of 2026-2027. In fact, NOAA's latest monthly projection has nearly a 100% chance of El Niño conditions lasting through the winter season.

In the image below, the x-axis shows the probability of El Niño, La Niña, or Neutral conditions for 3-month overlapping periods, with JFM corresponding to January-February-March, for example. 

In terms of the strength of this El Niño episode, the questions at this point really are whether or not this will be merely a "strong" El Niño event or a "super" El Niño event, and whether or not this will be a record-setting event as some models are projecting.

NOAA has steadily increased its projected strength in its probabilistic forecasts in recent months. And as of June, they are now projecting about a 60% chance of "very strong" or "super" El Niño status being met by late fall and early winter.

The International Research Institute for Climate and Society's ENSO Model is also going big with its forecast. In particular, its dynamic model (physics-based) member average has peak SST anomalies of 2.0º to 2.5ºC, which is in the "super El Niño" range, whereas its statistical model (history-based) analog average is in the merely "strong" range of 1.5º to 2.0ºC. 

The European (ECMWF) Seasonal Model projection is the most eye-opening. This model has admittedly been known for warm SST biases in emerging El Niño events in the past, but so far it has verified quite well with the onset of this event, and if anything, has been too cool so far this spring.

Also, the European Seasonal Model was among the first to really start picking up on this emerging El Niño signal early last winter, which is an impressive lead time. 

The individual members of the June 2026 European Seasonal Model (multiple simulations with slightly different initial conditions) project Niño 3.4 sea surface temperature anomalies to peak between 3.0º and 4.0ºC by late fall 2026.

This would put this El Niño event in the conversation of the strongest on record, even if the lower-end projections of this range were to verify.

Historical Super El Niño Events:

Since 1950, there have been three "Super El Niño" events in which monthly sea surface temperature anomalies in the Niño 3.4 region of the Pacific exceed 2.0ºC.

• 2015-2016: Monthly Niño 3.4 SST anomalies peaked at +2.57ºC in Nov 2015, making this the strongest El Niño (at least by this metric) in modern times. This El Niño event was strongest between Sep 2015 and Feb 2016 before fading to neutral conditions in Apr 2016.
  
  
• 1997-1998: Monthly Niño 3.4 SST anomalies peaked at 2.42ºC in Nov 1997 and again in Jan 1998. This El Niño event was strongest between Sep 1997 and Feb 1998 before fading to neutral conditions in the Niño 3.4 region by May 1998. However, Niño 1+2 SST anomalies remained high (east-based El Niño) through the summer of 1998.
  
  
• 1982-1983: Monthly Niño 3.4 SST anomalies peaked at 2.43ºC in Jan 1983. This El Niño event was strongest between Oct 1982 and Feb 1983, but notably, El Niño conditions persisted in the Niño 3.4 region until the summer of 1983 and in the Niño 1+2 region until the fall of 1983.

One theme you may notice here is that the highest SST anomalies in the Niño 3.4 region usually occur in late fall to early winter, although the atmospheric response tends to linger even beyond when these peaks occur.

Another thing I found interesting is that the 97-98 and 82-83 El Niño events lingered well into the spring and summer months, whereas the 15-16 event, while a little bit stronger overall, faded earlier in the spring compared to the other two years. 

Looking far back in history, one other noteworthy Super El Niño event occurred in 1877-1888, and this was significant from a historical perspective as it was associated with widespread famine events around the world.

According to a NOAA research paper published in 2020, modeled reanalysis SST anomalies for the 1877-1888 event in the Niño 3.4 region ranged anywhere from 1.8º to 3.5ºC, so it's not clear whether or not this was stronger than the other events mentioned. But at the very least, it was on par with these other super El Ninos.

Strong to Super El Niño Influences on North American Winter Weather:

During the cool season (fall, winter, early spring), El Niño tends to favor a strong subtropical jet stream that leads to more storms and wetter conditions across the southern tier of the U.S., while the polar jet stream often remains situated further north than usual, leading to fewer Arctic air surges southward into the Lower 48.

All other factors equal, during stronger El Niño phases, the above pattern is more likely to play out as the dominant winter pattern type. But of course, every year is going to look a little bit different, and there are other factors to consider as well.

Generally speaking, during El Niño winters, precipitation tends to be above average along the West Coast, across the southern-tier states, and along the East Coast. Snowfall in the East can be very boom or bust, given the wet and warm signal and whether or not precipitation during major storms falls as rain or snow. 

The snowfall signal is often less clear across most Interior ski regions, however, and necessitates a closer evaluation in terms of the strength, structure, and timing of El Niño phases, along with other oceanic-atmospheric signals such as North Pacific sea surface temperatures, Atlantic sea surface temperatures, and QBO (Quasi-biennial Oscillation, which is a measure of trade winds in the Pacific).

There is also the question of whether or not this potentially record-setting El Niño (still a big "if" but a very real possibility) could throw some curveballs into the overall weather pattern and lead to some unexpected outcomes.

Stay tuned for our initial winter forecast in August, which will dive more into these specifics.

As far as temperatures go, strong to super El Niño years tend to favor above-average temperatures across much of North America as cold air stays bottled up further north near the Arctic.

However, across the Southwest, there tends to be a cooler or even neutral signal compared to other regions in terms of temperature anomalies, likely due to an increased frequency of low-pressure systems tracking directly through this region compared to non-El Niño winters. 

Just for fun, let's take a look at Western U.S. snowpack anomalies on April 1st during the last three Super El Niño winters.

2015-2016:

During the most recent Super El Niño, snowpack was close to average across most of the West, but below average across much of the Southwest, where we usually expect deeper winters during El Niño.

1997-1998:

This was a deep winter across California, Utah, and the Southwest, while the Central Rockies and Cascades were near average. The Northern Rockies were a bit below average, but not excessively so.

1982-1983:

This was also a deep winter for California, Utah, and the Southwest, and Colorado also had a very strong season. In fact, most of the West did well this winter, aside from the Washington Cascades, where snowpack was below average. 

Each of these three winters had a very different look, though 82-83 and 97-98 were more similar to one another compared to 15-16.

We have a lot more data to sort through than just these three data points before we publish our winter forecast for 2026-2027. 

Stay tuned for our winter forecast preview for North America (East and West included), which will be published in August.

Thanks so much for reading!

Alan Smith