We’ve been seeing lots of speculation about what’s coming next in terms of California’s always confusing weather patterns. Newspapers and other media outlets have been full of stories.
The headline right now is that many signs point to the possibility of a powerful El Niño weather pattern this coming winter. And this is leading to speculation about the end of our four-year-long drought.
Long-term weather forecasting is a tricky business. Before we get too excited, we should remember that at the beginning of last summer, forecasters were also seeing signs of the development of an El Niño. That did not occur, and its failure is a useful reminder not to count too much on weather patterns before they actually occur.
And the confusion goes beyond that. Contrary to general public expectations, El Niño winters in California are far from uniformly wet. Some of our driest recorded “wet seasons” came during El Niño winters.
What really counts is how strong an El Niño we have. This is usually measured in terms of the divergence from average of surface sea temperature in critical portions of the far western Pacific Ocean. This year, so far, the degree of divergence is large, and that is a good sign.
So if an El Niño continues to develop, and if the resulting situation turns into a “strong” El Niño, will this be the end of our drought?
The answer depends on how you measure such things. For this coming winter to completely erase the water deficit now plaguing California, we’d have to have a roughly 200% of average winter over the entire state. (Remember that in recent years, we have been averaging about 20-40% of average.)
Stop and think about that for a minute. It sounds good, but be careful what you ask for. Such a winter would see large-scale flooding and destruction. Under such circumstances, we might find the end of drought to be even more expensive and disruptive in the short run than the drought itself.
All of this forecasting, of course, is based on a big assumption – that the weather in the future will continue to follow the same rules as in the past century or so. For many reasons, that is not necessarily true. Weather systems are driven by atmospheric heat, and now that we have warmed the planet, there is no guarantee that things will work exactly as they used to.
A good example of this is the continuing pool of relatively warm ocean water along the Pacific Coast from California north to Washington State and beyond. – a large scale, game-changing phenomenon that we have not seen in modern times.
There has been much speculation that this ocean warmth may have been one of the causes of the dryness the past few winters, but such thoughts are just that – informed speculation.
How might this coastal warmth interact with an El Niño weather pattern? No one really knows.
What we do know about this warmth, however, is that this past winter it raised snowlines in the mountains of California all winter and thus very significantly reduced our snowpack and resulting spring runoff.
Might the same thing happen in an El Niño winter? The possibility is very real.
So, even more than usual, our ability to anticipate what comes next for California’s climate is quite limited. We’re headed off into uncharted territory, with nothing more than past experience and computer models to tell us what to expect.
Should be interesting.
(c) Wm. Tweed