As of late September, confidence is growing that we will head into a weak La Niña ENSO phase during the winter of 2025-2026, whereas before, it was looking like roughly equal chances of a Neutral or La Niña.

However, a new player in the seasonal outlook has also emerged, which is the Pacific "Blob" – a term coined by Washington State Climatologist Nick Bond to describe a large area of anomalously warm ocean temperatures in the North Pacific Ocean.

OpenSnow Winter Forecast Preview Refresher:

First, let's revisit the Winter Forecast Preview for North America that we published back in mid-August.

In this winter forecast preview, we projected higher odds of above-normal snowfall in Western Canada, the Northern U.S. Rockies, the Upper Midwest, and the Northeast, and higher odds of below-normal snowfall over portions of the Western U.S., including California and Utah.

In this winter forecast preview, we also projected higher odds of below-normal temperatures across much of the Eastern and Central U.S., as well as the Northwest, with higher odds of above-normal temperatures across the Southwest. 

No adjustments are needed to this outlook for now, but we are keeping an eye on some emerging trends in ocean-atmosphere signals that could influence the upcoming winter season.

La Niña Potential is Increasing

As of mid-September, ENSO conditions remain "Neutral," but are trending toward La Niña. The latest weekly sea surface temperature anomaly in the Niño 3.4 region of the Eastern Equatorial Pacific is -0.4ºC.

This is just shy of the -0.5ºC threshold needed to reach La Niña, though technically, this threshold must be met for five consecutive 3-month overlapping periods for this to officially be classified as a La Niña. 

Long-range climate models have steadily been trending toward a weak La Niña episode developing during the fall and winter season of 2025-2026.

The European Seasonal Model projects a clear La Niña cool anomaly signature in the Central and Eastern Equatorial Pacific Ocean, peaking in November and December, before gradually trending back toward Neutral by March.

NOAA's latest probabilistic outlook now has a 71% chance of La Niña from October to December. Heading into mid-winter (Dec-Jan-Feb), La Niña is still favored, then Neutral conditions are favored to return by late winter and spring of 2026.

Image: NOAA Forecast showing the probability of an El Niño, La Niña, and Neutral phase for each three-month period between the fall of 2025 and the spring of 2026. Blue bars show the percent chance of La Niña, red bars show the percent chance of El Niño, and gray bars show the percent chance of Neutral. The “DJF” label is for “December-January-February”.

The International Research Institute for Climate and Society's model suite is projecting a weak La Niña episode, with model average sea surface temperature anomalies in the Niño 3.4 region between -0.5ºC and -1.0ºC.

For perspective, anomalies of -1.0 to -1.5ºC would qualify as a moderate La Niña, and anomalies of -1.5ºC or colder (for five consecutive three-month overlapping periods) would qualify as a strong La Niña. 

While the potential for La Nina is growing, ocean temperature anomalies in the North Atlantic Ocean are also projected to remain colder than average through the winter season – a signal known as a cold AQM, or Atlantic Quadpole Mode.

Thanks to research from OpenSnow forecaster Luke Stone at the University of Utah, we now know that sea surface temperature anomalies in the North Atlantic Ocean alter the alignment and strength of the correlation between El Niño and La Niña and winter precipitation in North America.

Results from Luke's research highlighted in the red square indicate a higher probability of above-average precipitation (and thus snowfall) over the Northern Rockies and Upper Midwest during La Niña and Cold AQM winters, and a drier signal across Oregon, California, and the Southwest U.S. This is a similar look to the Winter Forecast Preview we published in August. 

The image above shows precipitation patterns associated with Pacific Ocean water temperatures (La Niña, neutral, El Niño) and Atlantic Ocean water temperatures (Cold AQM, Neutral AQM, Warm AQM). Green shows areas of above-average rain and snow, while brown shows areas of below-average rain and snow. Source: Luke Stone, University of Utah.

The Pacific Blob

A new trend we are also keeping an eye on is the emergence of the Pacific Ocean Blob, which is more informally referred to as "The Blob". 

The Blob refers to a large area of well-above-normal ocean temperatures in the North Pacific Ocean, extending from the West Coast of the Contiguous U.S. to the Gulf of Alaska.

According to NOAA, the North Pacific area-average monthly sea surface temperature anomaly was the warmest on record during August, hitting an average of 20ºC for the first time in recorded history (records dating back to 1854).

These warm anomalies have eased somewhat recently, but the entire North Pacific Basin remains much warmer than normal.

The big question is whether or not "The Blob" will persist into the winter season. If it does, it could have significant impacts on North American weather as these persistent warm ocean temperature anomalies tend to favor high-pressure ridging, and thus fewer storms, along the West Coast of the U.S. and especially in California.

This pattern of West Coast ridging would also increase the likelihood and frequency of cold outbreaks into the Central and Eastern U.S.

How Has the Blob Influenced Winters in the Past?

The most significant period that featured a significant, persistent, and long-duration Blob was from 2014 to 2016.

This stretch coincided with warmer and drier winters over California and Utah, and colder and snowier winters across the Eastern U.S., while areas from the Colorado Rockies to the Pacific Northwest saw mixed results. 

However, the Blob was strongest during the winter of 2014-2015, and this coincided with below-average snowfall across nearly the entire West.

Interestingly enough, the winter of 2015-2016 was better across most of the West, as the Blob still existed in a weaker state, while a strong El Niño was also present.

This loop shows snowpack compared to average on April 1st during the Blob winters of 2014, 2015, and 2016 (the exact date/year for each image is displayed in the box in the bottom right-hand corner).

The Blob also made an appearance during the winters of 2018-2019 and 2019-2020. However, the Blob was weaker and less consistent during these winters, and snowfall was more abundant across the West in each of these winters.

In other words, The Blob is more likely to have a negative impact on Western U.S. snowfall if it is very strong and also very persistent, such as what occurred in the winter of 2014-2015.

Blob Uncertainty for 2025-2026

While a record-setting blob in August 2025 might seem like an ominous sign for the winter ahead in the Western U.S. (and perhaps a positive sign if you are rooting for a cold and snowy winter in the East), it is far from certain that a strong Blob will persist through the winter season.

Blob Persistence – There have been past years in which a strong Blob emerged late in the summer only to fade heading into the winter. Persistence is key here. The longer a strong warm air Blob persists in the North Pacific, the harder it is for this pattern to break.

A strong blob that lasts for a long time (many months or longer) is more likely to have an atmospheric response and impact predominant weather patterns.

Whereas, a shorter-lived blob that only lasts for a few months or less is easier to break down if frequent troughs and colder-than-average air masses track across the Gulf of Alaska and Northern Pacific with regularity, such as what occurred in the winters of 2018-2019 and 2019-2020.

There is little correlation with August sea surface temperature anomalies in the North Pacific and Gulf of Alaska, so we are still in wait-and-see mode to see if the Blob will persist later into the fall.

Model Projections – The European Seasonal Model is somewhat encouraging for the West, as the extreme warm anomalies are projected to gradually weaken over the course of the fall and winter, to a less extreme and less widespread signal by mid to late winter.

Even if the Blob doesn't disappear entirely, if it were to weaken enough, in theory, it would have less of an influence on predominant weather patterns.

La Niña Response – In recent past winters with a strong Pacific Blob present, ENSO conditions were either El Niño or Neutral, but not La Niña.

We have not had a comparable winter in which both La Nina conditions and a strong Blob were present simultaneously. If that were to occur this year, it's unknown how the atmosphere over North America may respond.

Final Thoughts

While we are gaining some clarity on a likely weak La Niña and cold AQM episode, the potential for a strong Pacific Blob adds a wrinkle to the seasonal outlook, and confidence is low on whether or not the Blob will persist through the winter 2025-2026 season.

For now, we are not making any changes to our winter seasonal outlook, but we will continue to monitor these ocean-atmosphere signals over the coming months.

And as always, we want to remind you that seasonal forecasts should always be taken with a grain of salt, even from the most credible sources. The accuracy of seasonal forecasts is much lower compared to short and medium-term weather forecasts.

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When it comes to skiing, it’s all about timing.

Booking a trip 7-10 days in advance and for a general area that looks stormy will increase your chances of scoring the best conditions.

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Alan Smith