The global climate responds sensitively to major oceanic shifts, especially changes in ocean temperature and wind circulation. These fluctuations are tracked closely because they play a crucial role in shaping seasonal weather across continents. A detailed look at the Pacific Ocean reveals significant changes as the La Niña phase concludes, prompting atmospheric transitions that could influence summer conditions in the U.S. and Canada and offer hints about the upcoming winter.
The La Niña phenomenon, part of the broader El Niño Southern Oscillation (ENSO), marks the colder phase of a recurring cycle in the tropical Pacific Ocean. ENSO shifts between cold and warm phases every one to three years, often beginning in late summer or early fall and persisting through the spring. Some instances, however, have extended up to two or three years.
In this context, La Niña refers to cooler-than-normal sea surface temperatures in the central and eastern Pacific, while El Niño represents the opposite—warmer-than-average conditions. These phases bring about notable differences in atmospheric pressure. As described, “During an El Niño, the pressure over the tropical Pacific is lower, with more rainfall and storms in this region. But during a La Niña, the pressure rises over the region, creating stable conditions and fewer storms over the equatorial Pacific.”
These shifts in pressure eventually impact global atmospheric circulation, affecting weather patterns across both hemispheres. Analyzing anomaly data from early 2024 shows a temperature decline starting in December and bottoming out in January, with La Niña fading by March. “As you can see, they were all typically coldest around January,” noted the study. Historical comparisons show that several past La Niña events transitioned into El Niño phases before the following winter, while others saw a return of La Niña.
Recent ocean analyses highlight weakening cold anomalies in ENSO zones, signaling the end of the 2024/2025 La Niña. “You can also see that warmer anomalies are emerging in the ENSO area. This has raised the overall temperature in the region, officially ending the weak La Niña phase of the 2024/2025 season.” A video based on monthly ocean data confirms this trend, documenting the retreat of cold anomalies and the rise of warmer waters.
Beyond surface-level temperatures, wind and subsurface ocean patterns play a vital role. A graph of temperature anomalies in the ENSO 3.4 region illustrates a post-January warming trend that reached neutral levels by March. Meanwhile, surface anomaly graphics from a broader region reveal cooling from November to February, followed by neutral conditions emerging in April.
Examining subsurface temperatures shows that although cold water masses still exist at depths of up to 150 meters in the central Pacific, the surface layer has warmed, especially in the east. “The cold pool of the La Niña is still visible… But its surface features have been eroded, with warmer waters also rising in the eastern regions.”
With La Niña concluded and its winter evolution understood, historical analogs help predict what might come next. La Niña typically leaves atmospheric imprints during winter and spring, but these fade as ENSO conditions stabilize. The transition from cold to neutral ENSO is expected to spark notable atmospheric changes.
Comparing current data with years that followed similar La Niña-to-neutral transitions reveals valuable insights. Compiled weather patterns from those years show distinct features, such as “a high-pressure area over Canada, also covering the northern and western United States and eastern Canada,” with “a weak indication of a low-pressure area” over the southern and eastern U.S.
Interestingly, current summer pressure forecasts display similar traits, including high-pressure zones over western and eastern Canada and signs of low pressure over the eastern U.S. “This shows us that some atmospheric features can result from having similar oceanic conditions.”
Looking at temperature patterns during similar transitions, historical records show warmer-than-average conditions in the western and northern U.S. and Canada, while some regions like the eastern U.S. and Pacific Northwest recorded cooler temperatures. Current forecasts align with this to some extent. “We do not see any below normal temperatures forecast over the eastern United States, we do see an area of near normal temperatures.”
The cooler temperature anomaly over the eastern U.S. is attributed to a corresponding low-pressure zone, which moderates temperatures compared to the western half of the continent. While extreme heat may not dominate the entire continent this summer, signs point to a milder or more typical summer for the eastern U.S.
As attention shifts toward the longer-term outlook, forecasts for ENSO into autumn and winter 2025/2026 become vital. The latest data from ECMWF projects no strong anomalies, suggesting continued neutral conditions through autumn. “It shows a lack of any significant anomalies, either warm or cold. This indicates a continuation of a neutral phase into Autumn, and likely towards Winter 2025/2026.”
Long-range ensemble forecasts reinforce this idea, placing most projections within the warm-neutral phase. While there’s still a possibility of another La Niña, it’s currently seen as unlikely. As mentioned, “There is also a chance for a new La Niña event, but based on the past years, that scenario is at the present time less likely.” Instead, there’s a growing possibility of a new El Niño arriving in 2026.
To understand what a stable neutral ENSO might mean for winter, analog years once again offer insight. Examining the November to March timeframe reveals a trend of low pressure over Canada and high pressure over the North Pacific following La Niña events. Though far-off forecasts are often unreliable, CanSIPS modeling data echoes this historical pattern: “A low-pressure zone over Canada and a high-pressure zone in the North Pacific.”
These patterns often create cold-air reserves in western Canada, driven by low-pressure systems that generate strong northerly winds. “That northerly flow brings colder air down from the polar regions, and creates a broad area of cold air reserve.”
This stored cold air can move into the United States when pressure patterns shift, bringing cold spells. CanSIPS projections—used more for trend analysis than precise forecasting—support this possibility by showing a large cold-air mass extending into the U.S.
Ultimately, examining past winters suggests that when oceanic and atmospheric setups align, they can lead to recurring seasonal patterns. As the report concluded, “Just like 1+1 equals 2, we can also see in the weather how a combination of certain global factors can produce a similar winter season more than once.”
Thus, with La Niña officially behind us and a neutral ENSO state prevailing, North America is poised for a relatively typical summer in the east and a potentially cooler, variable winter ahead—depending on how ENSO conditions evolve into 2026.
