Weather Wise - Weather Forecast
published: July 15th 2016
by: Brian Bledsoe
La Niña Transition
Let's see how our transition from El Niño to La Niña is going… Here is a look at the current sea surface temperature anomalies:
The blue shading that you see extending off the west coast of South America represents cooling taking place in that part of the Pacific Ocean. However, while that is happening the rest of the Pacific Ocean is still quite warm. This is especially true in the northern hemisphere... Thus, the Pacific Decadal Oscillation (PDO) remains quite positive. In my opinion, this has been very key to us not having to deal with the redevelopment of widespread regional drought in the Western or Southern Plains. However, it is getting quite dry for some of us and likely going to get drier… As you know, it has been my belief for a while that the PDO will revert back to a colder/negative phase during the next year or so.
Upper oceanic heat content has been in a cooler/negative state since the spring. This signals the transition out of El Niño and likely toward a La Niña. We haven't reached La Niña status yet, and it will likely take a while to do so.
The above charts show a very pronounced cold pool of water near and just below the surface in the main El Niño-Southern Oscillation regions of the Pacific. As we've mentioned before, this is likely another clear cut signal that La Niña is on its way.
The thing that I want you to take away from the above discussion is this: El Niño is gone, La Niña is on its way, and the PDO is still in a very warm/positive mode. This sets us up for a La Niña of some strength (to be determined) with a likely warm/positive PDO. That is a pretty rare combo, and is pretty hard to accurately analog based on the data we have available to us. More on that some other time. What type of impact is this transition likely to have? Check out what the North American Multi-Model Ensemble (NMME) is suggesting for the next couple months:
NMME Precipitation Forecast
The NMME suggests that the next four months will likely be drier than average, for parts of the Southern Plains and Gulf Coast Region. This is obviously not taking into account of any tropical storms that might impact the region.
The one interesting thing about this transition is that the PDO is NOT in a cool state right now like it was during the last La Niña. As I said early in this article, I believe that the very positive/warm phase of the PDO was very much responsible for keeping widespread and regional drought away from the Western and Southern Plains. The PDO is likely to stay warm/positive for a while longer. Will the PDO staying in a warm/positive phase help offset the traditional dryness caused by La Niña? I am working on that right now…