La Niña Update - December 2022

The animation below is of sea surface temperature anomalies for the past 90 days...

You can see toward the end of the animation there is less "dark blue" over a wider area than when the animation started. This is a sign that the La Niña has likely peaked and we will likely start to see it weaken in the coming weeks/months. Another sign is that the strong easterly winds in the tropics are forecast to weaken considerably after Christmas. The image below shows them being very strong through Christmas, and then they fade by late month and as we head into January.

The easterlies weakening will allow the stronger westerly wind bursts to make progress across the Pacific Ocean. The red numbers at the bottom of the above graphic represent MJO regions. For the past several weeks, whenever the MJO has tried to make significant progress out of region 6, it has weakened and faded. That is due to the strong easterlies essentially blocking its progress to the east. When the easterlies weaken, this will change and the MJO will become more variable and likely be allowed to cycle more frequently. That is a good sign...

Now, it isn't all perfect... Sometimes these transitions allow one area to become active and will shut down an area that has been active. For example, look at the projected precipitation anomalies for the next two weeks.

California has been quite active lately, and the state is progged to be quite dry for the next couple of weeks. Meanwhile, the Pacific NW and Northern Rockies remain very active. This is also classic La Niña. Farther east, the pattern looks like this...

Again, very La Niña-like...which should be the case given the strength of the easterlies through the end of the year.

What lies beyond those two weeks? Likely more of the same, as the analogs and the models suggested. During the month of January and during a La Niña, when the MJO gets into regions 6, 7, and 8, the pattern looks like this:

The green/yellow areas reflect ridges of high pressure, while the blue/purple areas reflect troughs of low pressure. MJO phases 6,7, and 8 during a La Nina in January will usually put a strong blocking ridge of high pressure. That means the coldest and most active weather sets up farther east. That doesn't necessarily mean there won't be storms in other areas, but that type of pattern usually favors the eastern half of the country. Again, this would be in January, IF we can get the MJO to cycle into these phases which looks possible at this time...

Back to the longer view of La Niña... The latest guidance from the IRI forecast continues to show what I've been showing you for the past several months. A La Niña that weakens and goes away as we finish winter and head into spring...

In fact, the probabilities above show a less than20% chance of La Niña existing by March, April, and May. It also shows the El Niño probabilities growing to 50% by July, August, and September. While that may not exactly mean immediate good news for everyone, I'll sure take it. The modeling from the same output is generating a precipitation anomaly forecast that looks like this...

JANUARY – MARCH

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APRIL – JUNE

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While the dry anomaly centered over the southwest part of the country is still present through the forecast period, it is noticeably weaker in the spring, than it is for late winter. I think this remnant dry anomaly forecast for April-June is due to the Pacific Decadal Oscillation still being in a negative phase. When that changes, and that could very well change in the back half of 2023, I would expect the dry anomaly to possibly go away. Plus, if we transition to an El Niño, there is even more evidence that it may go away. The dry anomaly would then likely focus on the Pacific NW, Northern Rockies, and Northern Plains. Still a long way to go for that change, but it is something I am watching closely...