What Exactly is El Niño and La Niña? Bonus: What does this mean for us?
El Niño and La Niña are weather catch phrases that are thrown around pretty frequently, but how many of us truly know what these features are? They are complex atmospheric-oceanic circulations, and to be honest, it's more than we could even explain in a short blog post, but we will cover some of the basics here.
Let's start with El Niño since we currently have these conditions in place. El Niño is the warm phase of the El Niño Southern Oscillation (ENSO) and refers to warming in the equatorial Pacific sea surface temperatures (SSTs) compared to normal. Here is a quick video explaining this phenomenon:
La Niña is the cool phase of ENSO and refers to cooling in the equatorial Pacific SSTs compared to normal. One more quick video to explain:
The strength of El Niño and La Niña episodes is determined by the difference in SSTs compared to normal and are measured in a region of the east-central Pacific Ocean known as the Niño 3.4 Region:
The Oceanic Niño Index (ONI) is a measure of the departure from the normal sea surface temperature in this region. This is the standard by which the strength of El Niño and La Niña episodes are measured. The average sea surface temperature in the Niño 3.4 Region is calculated each month and then averaged with values from the previous month and following month. This running three-month average is then compared with the average sea surface temperature for the same three months during the 1981-2010 30-year climate normal period giving a value for the ONI. Positive values of 0.5°C or greater reference the warm phase, or El Niño, while negative values of 0.5°C or less reference the cold phase, or La Niña. Curious how these have measured up through the years? All the values can be found here, or you can also check out this graph which shows January 1950 through late spring 2015:
Now that we know what these phenomena are, let's talk about what is really important - how does each impact us locally. Quick...is El Niño or La Niña more likely to bring the Sierra and northwest Nevada a wet winter? Do you have your answer? Chances are it isn't what you think. There seems to be the notion that El Niño equates to a wetter than average winter and La Niña the opposite. How many of you remember the incredible winter of 2010-2011? Here's a couple pictures to refresh your memory:
Being in the Sierra and northwest Nevada puts us right in between the greatest El Niño impacts, which brings better chances for rain to southern California and better chances for drier conditions to the Pacific Northwest. We have had both wet and dry El Niño years and La Niña years as well as ENSO neutral years. Unfortunately there is just not much correlation with ENSO for our part of the world. Since the 1930s we have had 6 strong El Niños and even these have ranged from dry to very wet in the Sierra and western Nevada. There have been two winters with particularly strong El Niños (1982-83 and 1997-98) and both of these winters were very wet in the Sierra with instances of significant flooding in both California and Nevada. However, this is only 2 data points in the admittedly short 65-year data set and does not guarantee that we will have a wet winter this year! Anyone who has lived in the region since the mid-1990s will likely remember the destructive January 1997 floods, but this occurred in the previous winter (1996-97) during an ENSO neutral year.
Now, I know what you're thinking...wasn't last year forecast to be an El Niño? Well, that is true, but the difference is last year we were in an ENSO neutral phase and only a weak El Niño was forecast, which took longer to develop than expected. This year we are already observing moderate El Niño conditions in the tropical Pacific Ocean (image below) with the forecast for it to only intensify. There is now high confidence in strong El Niño conditions persisting through the winter of 2015-2016 (strong being ONI values of +2 degrees C or warmer). I'm sure many of you have been hearing the hype about this being a "Godzilla-like" El Niño, and while a strong one is forecast, whether this becomes a record-breaker remains uncertain.
There is one other big question mark...the Blob! The warming in the eastern Pacific Ocean along the west coast is unprecedented and climate experts have no idea how this feature will interact with a strong El Niño. This "blob" has been linked to the ridge of high pressure which has been plaguing the west the past 4 years and could affect how El Niño drives weather patterns into California.
So, with all these details in mind, what does this mean for us here in the Sierra and northwest Nevada? The latest Climate Prediction Center outlook for January through March 2016 favors better than average chances for above normal precipitation from about Lake Tahoe south, with below normal chances favored in the Pacific Northwest. With this being said, however, it is only an outlook, not a guarantee, and confidence remains low to medium for our region. The other factor is medium to high confidence in above normal temperatures this winter, which could indicate an increased frequency of warm storms with high snow levels.
We know the drought is on everyone's mind and it would be incredible if we had a wet winter! Just remember, it took 4 years to create the precipitation deficits we now have, so it will take more than one wet winter to end the drought! If we combine the last 4 years, much of northeast California, the Sierra, and northwest Nevada are more than one year behind on precipitation. Even if we had the incredible winter of 2010-2011 again, we still wouldn't be caught up to normal.
For a great reference on the latest state of the ENSO and predictions for the upcoming season check with the Climate Prediction Center. You can also view our short YouTube video on El Niño which is our office's take on keeping it real with what you can expect for the upcoming winter.
Let's start with El Niño since we currently have these conditions in place. El Niño is the warm phase of the El Niño Southern Oscillation (ENSO) and refers to warming in the equatorial Pacific sea surface temperatures (SSTs) compared to normal. Here is a quick video explaining this phenomenon:
La Niña is the cool phase of ENSO and refers to cooling in the equatorial Pacific SSTs compared to normal. One more quick video to explain:
The strength of El Niño and La Niña episodes is determined by the difference in SSTs compared to normal and are measured in a region of the east-central Pacific Ocean known as the Niño 3.4 Region:
The Oceanic Niño Index (ONI) is a measure of the departure from the normal sea surface temperature in this region. This is the standard by which the strength of El Niño and La Niña episodes are measured. The average sea surface temperature in the Niño 3.4 Region is calculated each month and then averaged with values from the previous month and following month. This running three-month average is then compared with the average sea surface temperature for the same three months during the 1981-2010 30-year climate normal period giving a value for the ONI. Positive values of 0.5°C or greater reference the warm phase, or El Niño, while negative values of 0.5°C or less reference the cold phase, or La Niña. Curious how these have measured up through the years? All the values can be found here, or you can also check out this graph which shows January 1950 through late spring 2015:
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| The data for this graph was provided by the Climate Prediction Center (CPC), with the graph produced by Golden Gate Weather Services |
Believe it or not, this was a moderate to strong La Niña year!
Now, I know what you're thinking...wasn't last year forecast to be an El Niño? Well, that is true, but the difference is last year we were in an ENSO neutral phase and only a weak El Niño was forecast, which took longer to develop than expected. This year we are already observing moderate El Niño conditions in the tropical Pacific Ocean (image below) with the forecast for it to only intensify. There is now high confidence in strong El Niño conditions persisting through the winter of 2015-2016 (strong being ONI values of +2 degrees C or warmer). I'm sure many of you have been hearing the hype about this being a "Godzilla-like" El Niño, and while a strong one is forecast, whether this becomes a record-breaker remains uncertain.
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| This graphic from the Climate Prediction Center is showing sea surface temperature (SST) anomalies in the Niño 3.4 region |
There is one other big question mark...the Blob! The warming in the eastern Pacific Ocean along the west coast is unprecedented and climate experts have no idea how this feature will interact with a strong El Niño. This "blob" has been linked to the ridge of high pressure which has been plaguing the west the past 4 years and could affect how El Niño drives weather patterns into California.
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| Seasonal Sea Surface Temperature (SST) anomalies showing the "blob" and El Niño. |
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| A composite showing the overall pattern during the past 4 winters which has driven the west into a major drought. |
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| The official CPC outlook for January through March 2016 precipitation as of August 20, 2015. |
We know the drought is on everyone's mind and it would be incredible if we had a wet winter! Just remember, it took 4 years to create the precipitation deficits we now have, so it will take more than one wet winter to end the drought! If we combine the last 4 years, much of northeast California, the Sierra, and northwest Nevada are more than one year behind on precipitation. Even if we had the incredible winter of 2010-2011 again, we still wouldn't be caught up to normal.
For a great reference on the latest state of the ENSO and predictions for the upcoming season check with the Climate Prediction Center. You can also view our short YouTube video on El Niño which is our office's take on keeping it real with what you can expect for the upcoming winter.
