October Update: El Niño and '26-27 Winter Outlook
The first snows of the 2026-27 season fell on Oct 11 and 12, coating Tahoe's highest peaks with just a dusting. While the white accent atop the peaks may already be gone, anticipation surrounding the current El Niño and how it might affect precipitation and temperature outlooks for the winter remains top-of-mind for the snow obsessed.
So where are things? What's the status of El Niño and how are the seasonal outlooks evolving?
October El Niño Update: Heat continues to build
El Niño is a cyclical warming of waters in the eastern equatorial Pacific, typically occurring every 3-7 years as part of the El Niño Southern Oscillation (ENSO). This warming acts as a heat release for the planet, transferring heat and water vapor from the oceans into the atmosphere, altering global weather patterns in the process. Over the past year such an event has been building, possibly reaching record territory in the coming months. For more on El Nino basics, check out this explainer piece from earlier in the summer.
As of early October, the eastern Pacific continues to simmer. On October 12, sea surface temperature (SST) anomalies along both the eastern and central equatorial Pacific within the ENSO analysis regions, are more than 5°C warmer than normal. And along the west coast of Baja, SST anomalies are also ~5°C above average! While the warmth along the Baja and SoCal coasts was initially caused by a marine heatwave unrelated to El Niño from earlier in the spring, the combined excess heat in the Pacific has already had significant impacts on global weather, including fueling the hyperactive Pacific hurricane season and summer monsoon across the American Southwest.
To put all of this heat into the context of the official, 3 month El Niño average, this year's event has now reached a relative anomaly of 2.8°C over climatological norms. This places this year's event out in front as the strongest since 1982, well ahead of the notable El Niños of 1982, 1997, and 2015.
And even as temps. cool off in the mid latitudes, ensemble models remain in agreement that the Pacific will continue to heat up for the remainder of the fall, likely peaking around 3.34°C by some time in December.
Seasonal Winter Outlooks: October Update
The October seasonal projections from Copernicus, the European earth observation program, are out and much like September's outlooks, El Niño's influence on winter time precipitation and temperatures is impossible to ignore. These models combine the ensembles from nearly all global predictive services including NOAA, ECMWF (the Euro), CMC (Canadian), Japanese, etc., and blend them into one global "superensemble", depicting outlooks for the coming months, November - March.
Shown below are precip. and temp. mean anomalies, showing departures from normal in mm of liquid precip. and degrees Celcius from the 1993-2016 climate records.
Copernicus Global Ensemble for mean precip. anomalies compared to average from 1993-2016.
Copernicus Global Ensemble for mean temp. anomalies compared to average from 1993-2016.
Month by month, these outlooks show higher odds for a wetter and warmer than average winter. Precip. anomalies more heavily favor points from the Sierra west to the coast, while anomalies fall off east into the Great Basin. Temp. anomalies are also highest along the coast, becoming less pronounced further inland. This falls in line with the abundance of above average SSTs just off the California Coast, likely providing additional heat and water vapor to storms approaching southwest and westerly moisture fetches. Storms picking up added warmth and moisture as they arrive in California would likely promote warmer, wetter storms.
Such pronounced signals for above average precip. and temps. beg the question, just how extreme could these anomalies get?
Next up is a series of similar outlooks from the Copernicus ensembles analyzing the probabilities that precip. and temp. anomalies will fall in the upper 20% of climatology.
Copernicus Global Ensemble for precip anomalies exceeding the top 20% of winters from 1993-2016.
Copernicus Global Ensemble for temperature anomalies exceeding the top 20% of winters from 1993-2016.
Much like the mean precip. anomalies, the likelihood that precip. will fall in the top 20% of winters has a decent chance (40-50%) across the Sierra, with chances building into the heart of winter (Jan-Feb), but with the highest probabilities along the immediate coast, falling off further inland, especially east of the Sierra Crest.
As for extreme temperature anomalies, immediate coastal areas remain favored for the winter, especially in the late fall. The Sierra appears to have good chances for some much above average temperatures in the late fall and early winter, but these fall off towards the middle to back end of winter.
Conclusions
Forecasting exactly what effects this year's very strong El Niño will have on winter in Tahoe and when, remains impossible. Too many other factors, both known and yet to be known, can influence the earth system and short term weather patterns. However, of the many seasonal atmospheric oscillations and teleconnections, the magnitude of this year´s El Niño is akin to the loudest, shouting voice in a room full of chatter. Its magnitude overwhelms other atmospheric phenomena that would typically exert a larger influence in a more normal year.
Signals for a significant El Niño have been remarkably consistent across global models since last spring and continue well into the fall. Seasonal models for impacts in the late summer and fall also favored an above average Pacific hurricane season and active monsoon, primarily affecting the SW and southern California. Over the past few months, these impacts have largely played out as anticipated.
With flakes having flown and winter's chill soon arriving, it's time to see whether the skill of the models bears out in the cold season as much as it did in the warm.
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