La Niña itself is not nonsense, nor is the fact that as of Sep 8 La Niña conditions are observed in the tropical Pacific and expected by the National Weather Service Climate Prediction Center to continue through the upcoming Northern Hemisphere winter.
What has been nonsense over the past 2-3 weeks is news coverage of supposed consequences of that expectation. An egregious example appeared in the Tucson paper on Sunday. The article was headlined Another La Niña could be more bad news for the Colorado River.
The article quotes two experts. I'll call them Expert 1 and Expert 2. Their views are presented somewhat as a debate. Expert 1 enthusiastically supports the title of the article while Expert 2 says, Some La Niña years have produced near normal or above normal flows while others have seen much below normal flows as we have seen the last two years.
So an objective title for the article would have been Experts disagree on whether another La Niña could be more bad news for the Colorado River.
The National Weather Service Climate Prediction Center (the newspaper article links to the same web page that I have linked to above; hereafter CPC) as of Sep 8 quantifies their expectation of a continuation of La Niña conditions as a 91% chance from September through November, decreasing to a 54% chance in January-March 2023. The newspaper article provides those CPC numbers, but misrepresents the probabilities, which actually apply to something the CPC defines objectively. Ocean surface temperature anomalies are determined for a specific portion of the equatorial Pacific, lying roughly south through southeast of Hawaii. There is averaging over time and space to generate a single number. There is an arbitrary threshold, and an additional requirement for duration. The result is an objective answer: La Niña conditions, or not. But the newspaper article describes the 91% and 54% probabilities as chances of a La Niña weather pattern dominating the Northern Hemisphere.
I think of Northern Hemisphere winter weather patterns as rolls of the dice. Pacific Ocean temperatures and associated tropical weather patterns load the dice. If I were to literally roll a single dice (die) once every 15 days this coming winter, I might expect that by the end of the winter each side would have come up once: {1, 2, 3, 4, 5, 6}. Of course by dumb luck one or more sides might come up more than once this winter. Over the long run, if I repeat the experiment every year for many years I would expect the average roll to be 3.50. But let's say I have a second dice loaded in a way that makes it impossible for it to land with the 6 facing up. A potential 6 result will always be turned into a 1. So the set of expectations will be {1, 1, 2, 3, 4, 5}. Over the long run the average roll with the loaded dice will be 2.67, not 3.50. Does that mean that roll 1
dominated the winters when I used the loaded dice, or that I would call each 1 in those years a loaded result?
No, because one of the 1's would have happened anyway, and most of the time I still rolled a 2, 3, 4 or 5.
I expect there are people who will subjectively determine that the Northern Hemisphere midlatitudes this fall-winter will have been dominated by a La Niña weather pattern, no matter how the dice turn up. I have no idea how one would determine such a domination objectively, which would allow for a precise probability forecast calculated from historical data. I do know that the CPC issues probabilistic seasonal outlooks for precipitation. As I understand their discussion about those outlooks, they routinely adjust the historical data for recent trends, and that would mean they are somewhat siding with Expert 1 in the newspaper article (i.e., in effect, never mind that some La Niña years have produced above normal flows, look at the last two years with much below
). But even with weighting toward recent trends, the CPC is predicting equal chances for the three categories (below-normal, near-normal, above-normal) for western Wyoming for Oct-Nov-Dec 2022, with that equal chances outlook expanding to cover much of the rest of the upper Colorado Basin for Dec-Jan-Feb 2022-2023.
In summary, how would I quantify the word could
in the newspaper headline's phrase could be more bad news?
I would say more than 50% (where 50% would be "could be bad, could be good") but less than 60% (much less than the tone of the newspaper article). That's based in part on the fact that the 54% chance of La Niña conditions continuing into January-March 2023 is effectively a 46% chance of a return to neutral conditions by then.
