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Weather Wise

published: April 2nd 2021
by: Brian BledsoeIs La Niña Done?

Is La Niña Done?

In recent weeks, we have seen some changes take place with the ongoing La Niña episode, primarily in that it has weakened by quite a bit. The series of graphics below shows that trend.
Sea Surface Temperature Anomaly Change

Sub Sea Surface Temperature Anomaly Change

    Two very noticeable things are occurring: 1) the pronounced cold pool at the surface has warmed and almost disappeared and 2) the colder than average water that existed down to about 150 meters in the Central/Western Pacific has started to erode. It is not only eroding, but is being replaced by warmer than average water that is migrating eastward.
    Those two changes alone signify to me that this event is basically done. But let's look at a few other things before we completely sign off on that thought.
Equatorial Upper Oceanic Heat Anomalies

    You can see that we've been dealing with cooler than average equatorial ocean temperatures since last spring. Only recently have we started to return to average, and in some cases, a little above average.
IRI/CPC Model ENSO Predictions

    In the image below you can see that the majority of the models in the above graphic show us returning to "neutral" ENSO conditions in the next couple months. However, most of them do keep us a little cooler than average through the rest of the year.
    We are officially in the "spring unpredictability barrier", which means that the models struggle to resolve certain things during the spring. However, given the current situation from what I have shown above, I wouldn't anticipate a rapid return to moderate or strong La Niña conditions.
    So, what does that mean for us in terms of temperature and precipitation for the rest of the spring and summer? Here is what the updated IRI Multi-Model Probability is showing.
April - June Temperature Forecast

April - June Precipitation Forecast

June - August Temperature Forecast

June - August Precipitation Forecast

    You can see that there is a substantial tip in the probability toward a warmer than average rest of spring and summer. This is especially true for the western half of the country. There is also a tip toward drier than average conditions for parts of The Plains and much of the Western United States.
    While recent drought relief has been a huge help for parts of The Plains and Rockies, areas farther west and southwest have not been as lucky. Because of that, the regional drought footprint still exists and can always expand. That is something we'll be watching for in the next couple of months.