In a post eight weeks ago, I showed a scatterplot of the combined total September plus October precipitation at Tucson airport for each of the last 65 years versus the Oceanic Niño Index (ONI, defined by the Climate Prediction Center) for October of each year. This year the airport has had 2.40 inches in September (and more to come next week), which already puts this year's September-October total well above the median for the last sixty-five years. So far this year's September-October total is in the middle of the pack relative to the eight years that had an October ONI greater than +1.0 (as this year is almost sure to have).
The plot in this post is similar to the earlier post's September-October plot, except that now in this plot the Tucson airport rainfall is totaled for the five successive winter months of November through March, and the ONI is for January (the middle month of the five-month period). Selected years are labeled (the year is for the end of the five-month period).
I'm still no fan of drawing a straight line through the data points. Instead, the important consideration for this upcoming winter is that, of the eight previous winters for which the January ONI was greater than +1.0, all eight of those years are in the upper one-third of the five-month precipitation totals. No matter who in the Southwest gets clobbered this winter, Tucson will at least get decent pieces of the action. It's easy to forget that last winter's November through March total (the point labeled 15
) was already the 12th-wettest among the past 65 years. If this coming winter were only to match last year's total, it would still be a respectable showing for a moderate-to-strong El Niño winter.
I'm a contrarian in going with a 5-month winter, but that's the way it is in Tucson. Freezing temperatures can occur in November and March, although they are more common from December through February. Winter weather patterns can bring rain to Tucson in November and March, although on average they do so more often from December through February. It's important to bear in mind that even El Niño winters are feast or famine
—there can be periods lasting weeks, even a month or more, when the jet stream gets locked into a pattern unfavorable for rain in the Southwest. During the 1972-1973 El Niño most of Tucson's winter rain, 3.5 inches, came in November and March, while only 2.27 inches came in December through February. Similarly, 1957-1958's November plus March outperformed December through February. Conversely, and more typically, of the 10 inches in the five-month winter of 1965-1966, 9 inches came during December through February.
