La Niña calls it quits. Is El Niño paying us a return visit?
Thursday, February 16, 2017, 2:32 - La Niña has officially packed up and moved on, based on the latest official update from NOAA, but what's next? Is another El Niño in the works, or will we see "La Nada" for the rest of the year?
NOAA forecasters issued their latest update for what's happening in the equatorial Pacific Ocean last week, and it's looking like the weak La Niña - the cold phase of the El Niño Southern Oscillation (ENSO) that developed last September - has now ended.
In its place, we're seeing what's known as "ENSO-neutral" conditions, where sea surface temperature anomalies have evened out, especially across the central equatorial Pacific Ocean. As you'll see further down, however, there's a bit of a twist.
Weekly Pacific Ocean temperature anomalies (above/below normal), from November 23, 2016 to February 8, 2017. For context, the four Niña regions have been overlayed, including the Niña3+4 region used for NOAA's Oceanic Niño Index (ONI). Credit: NOAA/S. Sutherland
As the above animation shows, the La Niña pattern has definitely weakened over time, and temperatures in the central Pacific - the Niña 3+4 region, used by forecasters to gauge El Niño/La Niña - have evened out in the past few weeks. What we're left with is sometimes, colloquially, called "La Nada".
Looking at the eastern Pacific, though, it seems that rather than going back to the standard normal conditions (hot in the west and cool in the east), something has developed that looks a bit more like a classic El Niño (with heat concentrated in the east, along the coastline of Peru and Ecuador).
Pacific heat anomalies for the week end February 8, with Niño regions overlayed. Credit: NOAA/S. Sutherland
The only difference between this pattern and a full-blown El Niño is that the heat doesn't extend across the central Pacific. Temperatures across the Niño 3+4 region need to average at least 0.5oC (0.9oF) higher than normal for El Niño conditions to be considered in effect, and it has to sustain that for three months in order to warrant calling it an official El Niño.
SPRING IS AHEAD: How will a developing El Niño impact our spring weather? The Spring Forecast premieres Monday, February 27 at 9 p.m. ET
Effects on the U.S.?
How is the end of La Niña affecting winter and beyond across the U.S.?
If you recall, our forecast team did not anticipate this weak La Niña sticking around for long, in the first place. So, it wasn't expected to have a major influence on our winter weather.
Even so, this end to La Niña, along with the heat developing in the eastern Pacific, has had a moderating affect on weather in certain parts of the country.
"While we are months away from meeting the official criteria for El Niño, the sea surface temperature pattern in the tropical Pacific already resembles El Niño," says The Weather Network's Dr. Doug Gillham.
"The steady warming of sea surface temperatures to the west of South America (which was unexpected) likely contributed to the lack of sustained winter weather for parts of the Great Lakes and Northeast."
"Most computer models agree that neutral sea surface temperatures will continue for the next few months, and forecasters estimate an approximately 60% chance of neutral conditions lasting through the spring," says NOAA in a February 2017 ENSO update. "After that, it gets a bit more complicated. Some of the computer models are calling for a return of El Niño conditions by the second half of 2017."
As for winter's drought-busting precipitation in California, that was due to 'atmospheric rivers' which can form just as easily in La Niña years as El Niño years.
Flipping back to El Niño?
So, based on what's happening in the eastern Pacific, though, are we flipping right back into an El Niño from the La Niña?
The short answer is "it's possible."
According to what NOAA scientist Emily Becker wrote in Climate.gov's ENSO blog last week:
Our colleague Ken Takahashi of the Instituto Geofisico del Peru says that their country is officially in a "coastal El Niño" based on the anomaly in the Niño1.2 region. Note, this is very different from our definition of El Niño! Peru has experienced heavy rains and flooding over the past few weeks, which is expected when the Niño1+2 region warms substantially. Peru is affected both directly by the warm water on their coast, and indirectly by atmospheric circulation changes caused by sea surface temperatures in the central Pacific, whereas ENSO affects the U.S. only by the indirect "teleconnections."
Simply put, this warmth along the coast of Peru and Ecuador is only having a strong local effect, right now.
As Becker points out in her post, however, telling whether this is going to develop into a full-blown El Niño sometime later in the year isn't easy, at least at the moment. This is due to what's known as the "spring predictability barrier," which is a combination of the variability of a transitional season, like spring, and how the various ENSO computer forecast models work. She says that forecasting ENSO will become much easier once we approach the end of spring, and we are past that barrier.
As of now, though, the current forecast from NOAA and the International Research Institute for Climate and Society (IRI) gives a roughly 45-50 per cent chance that we'll see an El Niño by summer or fall. That's compared to around a 40 per cent chance of having neutral (or "La Nada") conditions, and only a 5-10 per cent chance of returning to La Niña. A roughly 50-40 split between El Niño and La Nada doesn't tell us much. It could come down to the flip of a coin right now.
ENSO probabilities for three-month periods, from Jan-Feb-Mar (JFM) to Sep-Oct-Nov (SON), 2017. Credit: IRI
The key, at the moment, is to keep an eye on what's going on in the eastern tropical Pacific, to see how that "coastal El Niño" develops in the weeks to come. Will it dissipate, or will it persist and spread westward?
Watch for our upcoming Spring Forecast, due out at the end of February, for more on what we may see for the months ahead.