Long-Range Fall & Winter Trends — El Niño News

Tuesday, August 11, 2026

El Niño continues to build, and some of the latest seasonal model guidance is forecasting extraordinary ocean temperature anomalies by late fall and early winter.

Both the ECMWF and CFSv2 ensembles are forecasting Niño 3.4 anomalies reaching around +4°C or higher near the peak of the event, with individual CFSv2 ensemble members approaching +4.5°C or higher.

Farther east in the tropical Pacific, some CFSv2 Niño 1+2 ensemble members are approaching +5°C during November and December.

Those are extreme numbers, and if anything close to them verifies, this El Niño would be among the strongest we’ve seen.

An Eastern-Based El Niño

One thing that continues to stand out is how strong the warming is across the eastern equatorial Pacific.

The Niño 1+2 region, located closest to the South American coast, has already experienced exceptional warming, while the warming continues to expand westward through Niño 3 and Niño 3.4.

The latest CFSv2 forecasts continue to show tremendous warmth in the eastern tropical Pacific into late fall, supporting the idea that we’re dealing with a strongly eastern-based El Niño.

At the same time, we need to remember that today’s tropical oceans are warmer than they were during many of the historic El Niño events we use for comparison. That makes comparing the absolute Niño numbers from this event directly against past events more complicated.

So while these model numbers are extraordinary, the ultimate question isn’t simply how warm Niño 3.4 becomes.

What matters for California and the Sierra is how the atmosphere responds to all that warm water.

What Does This Mean for Mammoth Through the Fall?

So how will this developing El Niño affect our weather over the next few months?

I’m still expecting above-average precipitation across the region during August and September.

Historically, El Niño hasn’t been much of a precipitation driver for us during October and November, and in some El Niño winters the more active California storm pattern doesn’t really get going until later in December.

There is, however, one wildcard I’ll be watching closely as we get into the second half of October and early November: a recurving western Pacific typhoon getting caught up in the mid-latitude flow.

A recurving typhoon can inject a tremendous amount of heat and moisture into the North Pacific pattern, helping amplify the downstream jet stream and ridge/trough pattern. If the timing and positioning line up correctly, that energy can contribute to a significant pattern change downstream several days later, potentially opening the door for an early-season storm into California and the Sierra.

That doesn’t mean a typhoon recurving in the western Pacific automatically gives Mammoth a storm, far from it. The location of the recurvature, interaction with the jet stream, and subsequent evolution across the North Pacific all have to line up correctly.

But during a year with this much going on across the tropical Pacific, a late-October or early-November recurving typhoon is one of the wildcards I’ll be watching for as a possible trigger for our first significant early-season Sierra storm.

Outside of something like that developing, I wouldn’t expect the main El Niño-driven winter pattern to necessarily show its hand during October or November.

That’s something I’ll be watching closely as we move through the fall.

The Winter Signal Is Getting Hard to Ignore

The bigger question is what this potentially historic El Niño will mean for California weather during the winter of 2026–2027.

This is where the latest data becomes particularly interesting.

The August ECMWF seasonal ensemble is showing an exceptionally strong wet signal across California for December, January and February.

The model is not simply showing an increased chance of above-average precipitation. It is showing 70–100% probabilities of above-average winter precipitation across California, with much of the state also showing a 70–100% probability of DJF precipitation finishing among the wettest 20% of winters.

That is an extraordinary seasonal signal.

It doesn’t guarantee that’s what will happen, but when a seasonal ensemble becomes that heavily weighted toward one side of the climatological distribution, it gets my attention.

For the Sierra Crest and Eastern Sierra, I’m continuing to lean toward well-above-average precipitation for the upcoming winter.

But There Is Still a Bust Scenario

We’ve all seen promising long-range winter forecasts fall apart before, and I’m not ignoring that possibility.

Even with everything I’m seeing right now, I’m leaving about a 30% chance that this does not work out the way the models are currently advertising.

The Pacific Ocean can give us all the right signals, but ultimately the atmosphere has to respond.

The location of the jet stream, blocking patterns across the North Pacific, storm trajectories and the timing of individual atmospheric river events will ultimately determine what happens here in the Sierra.

We could get to spring wondering what happened.

But that also means I’m currently putting roughly a 70% chance on a wetter-than-average winter for the Sierra.

That’s a pretty strong call this far out, and it’s based on how many different pieces of the puzzle are lining up in the same direction right now.

Wet Does Not Automatically Mean Record Snow

There is another important distinction to make.

A very wet California winter does not automatically mean a record snowfall winter at Mammoth Mountain.

Temperature matters.

With such tremendous warmth in the Pacific, I expect there will be storms this winter that carry a lot of moisture but also have higher snow levels.

Some atmospheric river events could bring rain into the lower elevations before colder air arrives and changes precipitation over to snow. Other storms could come in colder and produce tremendous amounts of Sierra snowfall.

The exact sequencing of those storms will make a huge difference.

That’s why I’m much more confident right now forecasting precipitation than I am trying to predict an actual Mammoth snowfall total this far out.

My Early Call for Winter 2026–2027

If I had to make my call for the upcoming winter based on everything I’m seeing right now, along with what I’ve been reading and learning from my trusted weather mentors, this would be it:

Well-above-average precipitation is expected for the Sierra, with higher snow levels at times, lots of base-building snowfall, and periods of rain mixed in at the lower elevations.

My confidence in a wetter-than-average winter is considerably higher than my confidence in exactly how much of that precipitation ultimately falls as snow.

There is plenty of time for this forecast to change.

We’re still months away from the heart of winter, and these seasonal models will continue to evolve as we move through late summer and fall.

But I’ve never seen the models showing an El Niño signal quite like what we’re looking at right now.

I was telling my wife over coffee this morning that this could end up being the biggest winter ever — or the biggest bust ever.

That’s really where we’re at.

The model signal is extraordinary.

The potential is certainly there.

But Mother Nature still gets the final vote.

We’re moving into largely uncharted waters, and it’s going to be fascinating watching how all of this unfolds over the next 6–8 months.

I’ll continue following the El Niño data, Pacific Ocean temperatures, seasonal model trends and, most importantly, signs that the atmosphere is actually beginning to respond to what is happening in the tropical Pacific.

Have a great day, and enjoy the weather — it’s all you got.

Steve Taylor — The Snowman MammothSnowman.com