September 08, 2023

Major El Nino Developing

The upcoming winter may be an interesting one for the West Coast.

A very strong El Nino is rapidly developing.   Strong enough that it could significantly alter the atmospheric circulation during the upcoming cool season, particularly after January 1.

As I have mentioned many times in this blog, El Nino is associated with warmer-than-normal sea surface temperature conditions over the central and eastern tropical Pacific.

The most frequent tool for monitoring the potential for El Nino (and its opposite La Nina) is the sea surface temperature averaged over an area in the tropical Pacific, known as the Nino 3.4 area (see map below)

Major changes have occurred this year as we transitioned from La Nina conditions (colder than normal temperatures in the Nino 3.4 area) to a moderate El Nino (see plot below). In the figure, the Y-axis shows the temperature difference from normal in that area.

We are now solidly a moderate El Nino and the tropical ocean is still warming.

A map of the sea surface temperature differences from normal (the anomaly) is shown below.  Mama Mia!  That is a warm equatorial ocean.

In the U.S. the NOAA/NWS Climate Prediction Center (CPC) is responsible for predicting El Nino and La Nina situations.  This is such a strong event and they are so sure that CPC is basically going a 100% for El Nino.

Why are they so sure?  Because both simulation models and statistical approaches are going for an increasing El Nino, as shown below.    We are talking about strong El Nino territory!
So what does a strong El Nino mean for our weather this winter?   

A warm tropical Pacific has an impact on the atmosphere that extends into the midlatitudes, particularly after the New Year.  In general, historical statistics suggest that the Northwest is a bit drier and warmer than normal and California gets more precipitation than normal.

Let's also check the latest seasonal simulation forecasts ( from NMME).  

The forecast for the precipitation anomaly from normal for January-March is for a dry Northwest and a wet California.  Classic.

And temperatures are predicted to be warmer than normal on the West Coast.

Let me make clear that the correlation between El Nino and West Coast weather is useful but not perfect.  

Think of it weighting the atmospheric dice.  But I would think carefully about buying that seasonal ski pass for a lower-elevation venue.


  1. Looks warm, but it also looks like a lot of clear days. And in the winter, for those who are no fans of near-freezing or sub-freezing temps, clear weather is exactly what most often produces freezing mornings. Without our insulating overcast from onshore flow, it can easily be 10 degrees colder in the morning than it might otherwise be. We always get such stretches, but this "warm" winter may be filled with them.

  2. Wasn't the last major El Nino around six or seven years ago? I remember the winter weather temps here in Portland being definitely above average, it rarely got below freezing, even at night. I also remember that the precipitation was above average, which alleviated the drought concerns, but also amplified the wildfire threats for the coming year. Thankfully, that wildfire season was below average, despite the increased plant and undergrowth from those rains.

  3. Is there any correlation between La Nina/El Nino and wind events?

  4. Very concerning for next spring and summer wildlife season.

    1. I agree, you should move as quickly away from this area as your feet will allow.

  5. To blair. I'm sure you were part of insurrection that stormed the capital, you Republicans are very hateful people that your cult leader Trump told you to do.

  6. I do hope we don't get another deficient rainy season; we are way, way behind now!. Aren't we due for a La Nada winter for a change?

  7. I hope so Cliff! The last few years east of the cascade crest have been brutal. Snow landed in October and was still going in June! This made it difficult and very dangerous to commute over Snoqualmie pass which saw more accidents and closures last winter due to a potent combination of very cold temperatures and dangerous driving. Plows were running constantly but unable to penetrate the solid ice that had bonded to the pavement (I believe you have written about this phenomenon in a previous blog) and so more snow kept piling up.


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