Variability—Elephants in the Room

Yesterday morning at 3:15 I awoke to rain, accompanied by occasional faint rumbles of thunder. My dream had ignored the thunder, but had not been able to reconcile the sound of the rain pelting down outside.
The PBS/NPR stations in Tucson spent the day reporting that, National climate experts are still waiting to see whether an El Niño weather pattern will develop. I don't have any idea who may be their source for that statement, but there are multiple problems with it. First of all, national climate experts have been expecting for at least a month now (see links in my previous post) greater chances for above normal precipitation in Tucson this winter, based mostly on the high chance of El Niño being present this winter. The Climate Prediction Center's outlooks are couched in terms of probability over a certain period of time (as are, or should be, almost all weather forecasts of precipitation). It is not a matter of waiting to see what happens. It's true that an official call on the actual presence of El Niño won't be made until a monthly update; the next monthly update will be on December 13. But El Niño being present (as defined by ocean temperatures) is not the same as a particular weather pattern being present. In every season, in every winter, in every El Niño winter there are a variety of weather patterns. One pattern gives way to another. Sometimes a pattern persists for weeks or even a month; sometimes a pattern lasts for less than a week. Over the course of a five-month winter there might be only a dozen or so pattern shifts. When it looks like an established pattern will never change to something else, it seems that's just when it does. Some patterns tend to return more frequently or last longer during an El Niño winter, and those patterns, averaged with the patterns that return less frequently or last for a shorter period of time in those years, result in what is a departure from an average winter. But every El Niño is different. There is no single El Niño weather pattern that develops and then lasts the rest of winter. As surely as some expert will eventually decree that such a pattern has arrived this winter, that decree will be followed by a shift to a dry pattern for a few weeks.
So every El Niño winter is different, and every non-El Niño winter is different. But intra-seasonal variability is not the whole story behind the scatter. The figure below simply repeats the data points plotted in the previous post. But now the color labels are different for the plotted points.

The entire period, beginning with the winter of 1949-1950, amounts to 69 years. In this figure, unlike the one in the previous post, for an approximate middle half of the period, the winters 1965-1966 through 1997-1998, amounting to 33 years, are plotted as green circles. There is a different distribution for the green years compared to the earlier and later periods. In 7 of the 33 green years the January ONI was greater than 1; 4 of those 7 were whopper winters in terms of precipitation. But also, of the 20 green winters that were not in El Niño territory in January, 4 of those winters were also whoppers. (I've always been skeptical of studies that purport to establish a lagged correlation between El Niño and rainfall. The lag works, until it doesn't. It is interesting to notice that 79 and 93 lagged 78 and 92 by one year, and 68 and 85 lagged 66 and 83 by two years. But most of the time a lag fails miserably, even in the green years.)
The end of the period of green years coincides with a shift from a warm to a cool phase of the Pacific Decadal Oscillation. But the start of the green years was near the middle of a cool phase of the PDO.
Although the El Niño winter three years ago was disappointing for Tucson, we've had a couple of winters this decade that nudged into green-year territory. It will be interesting to see what this winter may bring. We'll have to wait and see what will develop.