As some of you may have heard, El Niño is developing in the Central and Eastern Equatorial Pacific Ocean. Here is a look at the latest Sea Surface Temperature Anomalies, showing the area of warmer than normal water along the Equator.
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| Sea Surface Temperature Anomalies (degrees C) averaged from Aug 6th-Sept 2nd, 2023 |
If these anomalies persisted into the winter, we would be looking at a strong El Niño event. The Climate Prediction Center is calling for greater than a 60% chance of a strong event. So with the water already so warm, does this mean we can expect an impact from El Niño this fall? Great question.
We went back to take a look at previous events in October and November since 1980 where we were already in a Strong El Niño, or heading into one for the upcoming winter.
Let's start with temperature.
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| Previous Strong El Niño Events - October and November Temperature Anomalies |
There have been 5 cases since 1980 of this scenario, with the closest matches being 1982, 1997, and 2015 where we were already in a moderate or strong El Niño at this point. Green and blue colors mean cooler than normal, while yellow, orange, and reds warmer than normal. As you can see quite a bit of variability with even some cooler than normal fall's.
You may be asking with climate change, should we put more weight into the most recent event (2015) which was warm? Are we seeing warmer October's and November's with time? Let's look at a couple climate divisions over the region to see if there is a trend.
Northeast Washington October-November Average Temperature Trend
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As we can see, there is a little to no trend in temperatures for October and November.
So past strong El Niño events as well as long term trends are not telling us much about how this October and November will play out. What other sources do we have? The climate models are favoring a warmer than normal October and November according to the NMME (National Multi Model Ensemble).
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| NMME Temperature Anomaly forecast for October 2023 |
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| NMME Temperature Anomaly forecast for November 2023 |
What is the official outlook calling for from the Climate Prediction Center? Some tilting of the odds towards warmer than normal conditions from October-December (Note: 2 month outlooks are not produced).
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| Climate Prediction Center Temperature Forecast for October-December 2023, issued August 17th |
Conclusion for Oct-Nov Temps: While previous strong El Niño events as well as trends are not telling us much, the odds are tilted towards warmer than normal conditions.
What about precipitation this fall? Again we will begin with previous strong El Niño events to see what has happened in the past.
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| Previous Strong El Nino Events - October and November Precipitation Anomalies |
Precipitation shows less variability when compared to the temperature maps, with all five events giving us near normal amounts with minor location variability. What about long term trends in precipitation?
Northeast Washington October-November Average Precipitation Trend
East Slopes of the Cascades October-November Average Precipitation Trend
Similar to temperature, little to no trend.
What are the climate models showing? Here again is the NMME for October and November.
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| NMME Precipitation Anomaly forecast for October 2023 |
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| NMME Precipitation Anomaly forecast for November 2023 |
There is a weak signal towards drier than normal conditions, especially in October.
Finally, what is the Climate Prediction Center calling for?
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| Climate Prediction Center Precipitation Forecast for October-December 2023, issued August 17th |
Some tilt in the odds towards drier than normal conditions.
Conclusion: While previous Strong El Niño events have generally brought normal precipitation for October and November, the outlook shows odds slightly tilted towards drier than normal conditions.
Now that we have finally made it through November in this blog, what about the winter? Well that is a topic for a later blog post. But here is a little teaser...typically our El Niño winters are mild.
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