Fall Rain

Nice rainbows from about 5:30 - 5:45 PM last evening, near the end of and just after a dump of about half an inch. A faint secondary bow can be seen near the furnace exhaust stack. A short time before this photo, while it was still raining, both bows extended fully off to the northeast.

Tucson airport (misspelled Tuscon at the weather.gov site) has now had 1.29 inches so far in September. (Mine now stands at an even 2 inches.) My post last year discussed the September-plus-October rain for TUS. I won't repeat that, except for a short listing of a few data points already plotted in that post, limited to just the years where the previous winter had been a strong El Niño. The numbers (October Oceanic Niño Index; September plus October Rainfall, inches) are the same as described and plotted in last year's post.

Year	ONI	Rain
1958	0.5	1.42
1973	-1.7	0.00
1983	-0.6	9.26
1992	-0.1	0.97
1998	-1.2	1.34
2016	-0.5	1.29+

This year's October ONI is based on the CPC consensus forecast--currently expecting borderline neutral through the fall and winter. The year 1983 did in fact see a lot of rain in September-October, and it did follow an El Niño winter, but by October of that year the ONI was about where it is now expected to be this year. Nevertheless, it has become a legend about September-October 1983 that it was an El Niño year.
Given that history, it's a bit surprising that so far this fall there have been no Tucson sightings of El Niño laggings. Although it's very unlikely that we could get a significant tropical system over the next ten days, after that there is a period of a few weeks when the potential is high for another tropical system to affect Tucson. If that were to happen, I predict an outbreak of laggings that will quickly escalate into a full epidemic of El Niño year!